Metabolic reprogramming of the osteogenic lineage development throughout bone therapeutic<\/h3>\n
To map the metabolic modifications throughout bone regeneration, we first analyzed scRNA-seq information from murine fracture and management tissues utilizing uniform manifold approximation and projection (UMAP)-based dimension discount.36 This evaluation recognized completely different clusters representing bone resident and infiltrating cell clusters (Figs. 1a and S1a), together with: chondrocytes, osteoblast lineage cells (OBs), endothelial cells (ECs), bone marrow mesenchymal stem cells (BMSCs), mast cells (MCs), hematopoietic cells (HCs), clean muscle cells (SCs), megakaryocytes, and neutrophils. Throughout the mixed OBs and BMSCs subclusters, differentially expressed gene (DEG) and Gene Ontology (GO) enrichment analyses revealed that fracture damage considerably prompts vitality metabolism pathways, with a pronounced enrichment in mitochondrial ATP synthesis (Fig. S1b, c).<\/p>\n
![\"Fig.](\"https:\/\/media.springernature.com\/lw685\/springer-static\/image\/art%3A10.1038%2Fs41368-026-00460-5\/MediaObjects\/41368_2026_460_Fig1_HTML.png\")
<\/div>\nSingle-cell RNA sequencing reveals metabolic reprogramming of the osteoblast lineage throughout bone fracture therapeutic. a Uniform Manifold Approximation and Projection (UMAP) plot exhibiting the distribution of single cells from mouse fracture and management bone samples. b Heatmap depicting glycolysis and oxidative phosphorylation (OXPHOS) pathway densities throughout completely different cell clusters, calculated utilizing single-sample gene set enrichment evaluation (ssGSEA). c t-distribution of random neighborhood embedding (t-SNE) of BMSCs and OBs cell subclusters in fracture and management samples. d Re-dimensionality discount clustering and t-SNE distribution of osteoblast lineage clusters (together with BMSCs and OBs clusters) in fracture and management samples. e Glycolytic pathway rating of osteoblast lineage clusters alongside pseudotime trajectories within the fracture and management samples. f Expression patterns of glycolytic and osteogenic markers<\/p>\n<\/div>\n<\/div>\n<\/figure>\n<\/div>\n
Notably, UMAP density plotting confirmed that glycolysis was primarily restricted to mature lineages like chondrocytes and OBs, whereas OXPHOS confirmed a a lot wider distribution that included the BMSCs cluster (Fig. 1b). In contrast with the management group, the fracture damage group displayed greater OXPHOS scores throughout all mobile subclusters. Importantly, the upregulation of OXPHOS scores outpaced that of glycolysis, with this development being most distinguished in BMSCs (Fig. S1d). Concurrently, re-clustering of the osteogenesis-related cell subclusters (BMSCs and OBs) revealed a marked enlargement within the proportions of Fkbp10+ and Bglap\u2009+\u2009OBs following damage (Figs. 1c, d and S1e). To dissect the temporal dynamics governing this metabolic shift throughout osteogenesis, we reconstructed the BMSC-to-OB developmental continuum utilizing Monocle3 pseudotime evaluation (Fig. S1f). This trajectory unmasked a divergence: whereas management samples maintained secure metabolic baselines, fractured samples exhibited a pointy, progressive decline in glycolytic exercise alongside the differentiation timeline (Fig. 1e). Crucially, this attenuation of glycolytic flux coincided with a pronounced downregulation of the glycolysis-related gene Pfk household expression in the course of the transition from BMSCs to mature osteoblasts, signaling that dampening glycolysis is crucial to favor the OXPHOS-driven energetic calls for required for lineage development and bone therapeutic (Fig. 1f).<\/p>\n
PFKM capabilities as a metabolic checkpoint governing the glycolysis-to-OXPHOS shift and osteogenic differentiation<\/h3>\n
To validate whether or not the shift from glycolysis to OXPHOS is functionally required for BMSCs differentiation, we first handled rat BMSCs (rBMSCs) with metabolic inhibitors throughout osteogenic induction. Blocking mitochondrial ATP synthase with oligomycin A (1 and 5\u2009\u00b5mol\/L) considerably suppressed osteogenic differentiation, as evidenced by attenuated alkaline phosphatase (ALP) staining and exercise at day 7 (Figs. 2a and S2a). Subsequent reverse transcription quantitative polymerase chain response (RT-qPCR) evaluation revealed that oligomycin A markedly upregulated key glycolysis-related genes, notably hexokinase 2 (Hk2), Pfkm and phosphofructokinase, liver kind (Pfkl) (Fig. S2b). These information point out that whereas rBMSCs try to survive mitochondrial impairment by way of a compensatory shift towards glycolysis, this pressured glycolytic state is incompatible with regular osteogenesis.<\/p>\n
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<\/div>\nIdentification of PFKM as a metabolic checkpoint and its practical validation in selling rBMSCs osteogenesis and metabolic reprogramming. a Alkaline phosphatase (ALP) staining of rBMSCs handled with oligomycin A (1 or 5\u2009\u00b5mol\/L) for 7 days underneath osteogenesis (n\u2009=\u20093). b ALP staining of rBMSCs handled with 2-DG (200\u2009\u00b5mol\/L) for 7 days underneath osteogenesis (n\u2009=\u20093). ALP staining (day 7) (c), and Alizarin Pink S (ARS) staining (day 14) (d) in siPfkm and siNC teams underneath osteogenic induction (n\u2009=\u20093). qRT-PCR (e) and western blot (f) evaluation of osteogenic-related markers in siPfkm and siNC teams underneath osteogenesis (n\u2009=\u20093). Oxygen consumption fee (OCR) evaluation (g), glycolytic proton efflux fee (PER) evaluation (h) in siPfkm and siNC teams (n\u2009=\u20093). OI osteogenic induction (0, 3, 7 days) ALP staining of Pfkm-knockdown and management rBMSCs subjected to metabolic inhibition with oligomycin A (i) or 2-DG (j) after 7 days of osteogenesis (n\u2009=\u20093). Knowledge signify imply\u2009\u00b1\u2009SD. *P\u2009<\u20090.05, **P\u2009<\u20090.01, and ***P\u2009<\u20090.001 by Pupil\u2019s t check (e, g and h)<\/p>\n<\/div>\n<\/div>\n<\/figure>\n<\/div>\n
Provided that an elevated glycolytic baseline correlated with impaired bone formation, we subsequent examined whether or not direct pharmacological inhibition of glycolysis may conversely speed up differentiation. Paradoxically, the glycolysis inhibitor 2-DG (200\u2009\u00b5mol\/L) additionally considerably blocked osteogenesis (Figs. 2b and S2c). Whereas 2-DG therapy downregulated most glycolytic genes, Pfkm expression remained notably unchanged (Fig. S2d). This selective responsiveness advised that PFK, slightly than the everyday coordinated glycolytic community, would possibly act as a specialised metabolic checkpoint throughout osteogenesis.<\/p>\n
Baseline expression evaluation confirmed that Pfkm and platelet kind (Pfkp) ranges have been comparable ranges, each being decrease than Pfkl (Fig. S2e). To systematically examine the practical roles of those PFK isoforms, we utilized small interfering RNAs (siRNAs) to individually goal Pfkl, Pfkm, and Pfkp, deciding on the sequences with the best knockdown efficiencies for downstream validation (Fig. S2f). ALP assays revealed that the knockdown of Pfkm exerted a considerably superior pro-osteogenic impact in comparison with the NC group, Pfkl knockdown, Pfkp knockdown, or their mixture (Figs. 2c and S2g, h). CCK-8 assays confirmed that this enhanced differentiation was not a confounding artifact of altered cell proliferation (Fig. S2i). Moreover, Pfkm knockdown markedly accelerated extracellular matrix mineralization and superior osteogenic differentiation, as demonstrated by Alizarin Pink S (ARS) staining at day 14 (Figs. second and S2j), which correlated with a strong upregulation of key osteogenic markers at each the mRNA and protein ranges (Fig. 2e, f). In the end, the distinctive regulatory habits of PFKM prompted us to research its function in larger depth.<\/p>\n
To characterize the regulatory function of PFKM in rBMSC metabolism, we assessed mobile respiratory and glycolytic flux throughout osteogenic induction utilizing Seahorse XF know-how. Pfkm knockdown triggered a strong enhancement in mitochondrial oxidative metabolism, evidenced by considerably elevated oxygen consumption charges (OCR). In contrast with controls, siPfkm-treated cells exhibited greater basal respiration, maximal respiratory capability, ATP manufacturing, and spare respiratory capability, with this metabolic surge being most distinguished at day 3 of osteogenic induction (Fig. 2g). Concurrently, we evaluated glycolytic operate by monitoring the proton efflux fee (PER) and located that Pfkm knockdown markedly restricted glycolytic flux. Each basal and compensatory glycolysis have been considerably suppressed within the knockdown group (Fig. 2h). Crucially, this PFKM-directed metabolic rewiring was practical, as Pfkm knockdown partially rescued the osteogenic suppression initially induced by oligomycin A and 2-DG remedies (Figs. 2i, j and S2k, l). Collectively, these metabolic profiles verify that PFKM capabilities as a metabolic \u201cbrake\u201d on osteogenesis. Since osteogenic differentiation is inherently coupled with elevated OXPHOS, the focused suppression of Pfkm considerably accelerates this differentiation whereas concurrently boosting OXPHOS. This outcome signifies that PFKM enhances osteogenesis by performing as a important metabolic swap that drives the bioenergetic shift in rBMSCs.<\/p>\n
\n Pfkm knockdown initiates mitochondrial donut-shaped formation<\/h3>\n
To analyze the structural and practical penalties of the Pfkm-mediated metabolic swap, we subsequent evaluated the practical state of the mitochondrial community throughout osteogenesis. In comparison with the management group, the Pfkm-knockdown group exhibited considerably decrease mtROS ranges all through differentiation (days 0, 3, 7, and 14), whereas their mitochondrial membrane potential (\u0394\u03a8m) remained secure and comparable between teams (Fig. S3a, b). This suppressed oxidative stress correlated with a concurrent upregulation of uncoupling protein 2 (Ucp2) expression, suggesting that enhanced mitochondrial uncoupling serves as an endogenous protecting mechanism to mitigate mtROS manufacturing with out compromising membrane potential throughout lineage development (Fig. S3c).<\/p>\n
Past these biochemical alterations, MitoTracker staining revealed that Pfkm knockdown triggered a placing, time-dependent structural transforming of the mitochondrial community. Particularly, the mitochondrial reticulum transitioned from an elongated, interconnected community into fragmented, punctate varieties by days 3 and seven (Fig. 3a). Transmission electron microscopy (TEM) corroborated this morphological shift, capturing an elevated frequency of mitochondrial fission occasions accompanied by a concomitant discount in cristae density inside Pfkm-knockdown group (Fig. 3b). To exactly characterize this fragmentation, we employed structured illumination microscopy (SIM), which confirmed that these punctate constructions have been specialised donut-shaped mitochondria. Notably, whereas cristae have been clearly discernible in management cells, they have been largely obscured within the donut-shaped mitochondria of knockdown cells, indicating a profound reorganization of the mitochondrial ultrastructure (Fig. 3c). This structural distinction signifies a focused ultrastructural adaptation slightly than generalized, pathological mitochondrial harm.<\/p>\n
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<\/div>\nPfkm knockdown triggers donut-shaped mitochondrial transforming throughout rBMSCs osteogenesis. a Confocal pictures of rBMSCs stained with MitoTracker Deep Pink (left) and quantitative evaluation of mitochondrial facet ratio (proper) at days 0, 3, 7, and 14 of osteogenic induction in siPfkm and siNC teams (n\u2009=\u20093). OI osteogenic induction. Ultrastructural evaluation. Transmission electron microscopy (TEM) pictures (purple arrows point out constricted mitochondria) (b) and structured illumination microscopy (SIM) pictures of siPfkm and siNC teams staining with PK Mito Pink (purple arrows point out donut-shaped mitochondria) (c) following 3 days of osteogenesis (n\u2009=\u20093). Scale bars are as indicated. Knowledge signify imply\u2009\u00b1\u2009SD. *P\u2009<\u20090.05, **P\u2009<\u20090.01, ***P\u2009<\u20090.001 by Pupil\u2019s t check (b)<\/p>\n<\/div>\n<\/div>\n<\/figure>\n<\/div>\n
Provided that Pfkm knockdown concurrently accelerated osteogenesis and altered mitochondrial structure, we subsequent sought to make clear whether or not typical mitochondrial fragmentation alone is adequate to drive bone formation. We subsequently handled rBMSCs with both the mitochondrial fission promoter BC1618 or the fusion inhibitor MYLS22. Though each pharmacological brokers efficiently pressured mitochondrial fragmentation (Fig. S4a), neither therapy may replicate the sturdy pro-osteogenic outcomes triggered by Pfkm knockdown, yielding solely restricted enhancements within the osteogenic differentiation of rBMSCs (Fig. S4b). This modest enhancement advised that typical mitochondrial fragmentation alone couldn’t absolutely account for the superior pro-osteogenic outcomes noticed in Pfkm-knockdown cells. Consequently, we reasoned that Pfkm knockdown might set off a definite morphological and practical transforming past classical fission, a speculation we explored additional within the subsequent part.<\/p>\n
The donut-shaped morphology facilitates a complete MQC program involving mitochondrial biogenesis, mitophagy and Mito\/MDVs secretion<\/h3>\n
Provided that this \u201cdonut-shaped\u201d transformation sometimes serves as a structural precursor to superior organelle clearance, we subsequent characterised the broader panorama of MQC past mere morphological transforming. Evaluation of mitochondrial DNA (mtDNA) copy numbers indicated a considerable accumulation within the knockdown group relative to controls (Fig. 4a). This accumulation was accompanied by elevated expression of peroxisome proliferator-activated receptor \u03b3 coactivator 1-alpha (PGC-1\u03b1), the grasp regulator of mitochondrial biogenesis (Fig. 4b).<\/p>\n
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<\/div>\nDonut-shaped mitochondria accompany mitochondrial biogenesis and mitophagy throughout osteogenic differentiation. a Relative mtDNA copy quantity in siPfkm and siNC teams at days 0, 3, 7, and 14 of osteogenesis (n\u2009=\u20093). b Western blot evaluation of PGC-1\u03b1 protein expression in siPfkm and siNC teams at days 0, 3, 7, and 14 of osteogenesis (n\u2009=\u20093). c Western blot evaluation of autophagy and mitochondrial markers in siPfkm and siNC teams at days 0, 3, 7, and 14 of osteogenesis (n\u2009=\u20093). d TEM pictures exhibiting mitophagosomes within the Pfkm-knockdown group after 3 days of osteogenesis (n\u2009=\u20093). e Confocal pictures (left) and fluorescence line profile evaluation (proper) of LC3B (Pink)-mitochondria (Inexperienced) co-localization in siPfkm and siNC teams after 3 days of osteogenesis (n\u2009=\u20093). Scale bars are as indicated. Knowledge signify imply\u2009\u00b1\u2009SD. *P\u2009<\u20090.05, **P\u2009<\u20090.01, and ***P\u2009<\u20090.001 by Pupil\u2019s t check (a)<\/p>\n<\/div>\n<\/div>\n<\/figure>\n<\/div>\n
To verify whether or not accelerated degradation happens in tandem with this enhanced biogenesis, we evaluated key mitophagy markers throughout osteogenic induction. Pfkm-knockdown cells exhibited elevated LC3B-II ranges alongside a big clearance of TOMM20 and P62, indicating elevated formation of mitochondrial autophagosomes and accelerated lysosomal degradation (Fig. 4c). The induction of mitophagy upon Pfkm knockdown was additional confirmed by TEM imaging, which revealed distinct double-membrane constructions engulfing mitochondria (Fig. 4d). Moreover, immunofluorescence revealed a big enhance in LC3B-mitochondria colocalization, offering sturdy proof that Pfkm knockdown triggers heightened mitophagy (Fig. 4e). To analyze whether or not this accelerated mitochondrial turnover is immediately required for the pro-osteogenic phenotype, we handled Pfkm-knockdown cells with Mdivi-1, a twin inhibitor of mitochondrial fission and mitophagy, throughout osteogenic induction. Mdivi-1 therapy efficiently attenuated the heightened mitophagy flux triggered by Pfkm knockdown, as indicated by lowered mitochondrial-LC3B fluorescence colocalization, decreased LC3B-II ranges, and a rescue of TOMM20 expression (Fig. S5a, b). Morphological evaluation by way of mitochondrial staining additional revealed that Mdivi-1 largely reverted the fragmented, donut-shaped mitochondria again to an elongated, reticular community (Fig. S5c). Crucially, this pharmacological inhibition of fission and mitophagy considerably reversed the pro-osteogenic phenotype of Pfkm-knockdown rBMSCs, leading to a considerable discount in ALP exercise and ARS-stained mineralized matrix (Fig. S5d). Moreover, the autophagy inhibitor 3-methyladenine (3-MA) was utilized to additional validate these findings. In step with the Mdivi-1 outcomes, 3-MA therapy efficiently restored mitochondrial morphology to an interconnected community construction, which was accompanied by a rescue of TOMM20 expression and a concomitant lower in LC3B-II ranges. In the end, this pharmacological disruption of the mitophagy program additionally suppressed the pro-osteogenic results initially exerted by Pfkm knockdown (Fig. S5e, f, g).<\/p>\n
Given the noticed mitochondrial fragmentation and turnover, we subsequent investigated whether or not these cells launched mitochondrial parts into the extracellular house. Following the isolation protocol schematically illustrated (Fig. 5a), we extracted particulate parts from the osteogenic induction medium. Subsequent MitoTracker Inexperienced staining of the precipitate revealed a larger abundance of extracellular mitochondrial constructions\u2014encompassing each bigger fragments and smaller Mito\/MDVs\u2014within the experimental group, with whole particle diameters starting from 0.5 to five\u2009\u03bcm (predominantly 0.5\u20131\u2009\u03bcm) (Figs. 5b and S6a). Persistently, western blot evaluation confirmed enriched expression of the mitochondrial markers COX IV and TOMM20 within the experimental group (Fig. 5c). TEM revealed MDVs diameters predominantly starting from 70 to 100\u2009nm, in step with earlier reviews,37 and confirmed their elevated abundance within the Pfkm-knockdown group (Fig. 5d). To check whether or not these secreted mitochondrial constructions possess practical bioactivity, we carried out a co-culture assay. Stably expressing mitochondria-targeted GFP rBMSCs have been knocked down for Pfkm, and their secreted Mito\/MDVs have been collected and co-cultured with naive mCherry-expressing rBMSCs for twenty-four\u2009h. Confocal imaging confirmed that the recipient cells efficiently internalized these green-fluorescent mitochondrial particles (Figs. 5e and S6b). Remarkably, the internalization of those Pfkm-knockdown Mito\/MDVs considerably enhanced the baseline osteogenic differentiation potential of the naive recipient cells (Fig. 5f). Collectively, our findings illustrated that Pfkm knockdown promotes osteogenic differentiation by triggering a complete transforming of MQC, impacting mitochondrial dynamics (fission\/fusion), biogenesis, mitophagy, and the secretion of practical Mito\/MDVs.<\/p>\n
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<\/div>\nDonut-shaped mitochondria mediate the secretion of practical Mito\/MDVs, facilitating osteogenic differentiation in recipient cells. a Schematic illustration of the process for isolating secreted Mito\/MDVs from rBMSC conditioned medium. Confocal pictures (b) and western blot evaluation (c) of the remoted Mito\/MDVs from siPfkm and siNC teams (n\u2009=\u20093). d TEM pictures of remoted Mito\/MDVs (inexperienced arrows: double-membrane MDVs; yellow arrows: single-membrane MDVs; purple arrows: mitochondria) (n\u2009=\u20093). e 3D confocal pictures exhibiting recipient rBMSCs internalizing GFP-tagged Mito\/MDVs from virus-transduced donor cells after 24\u2009h co-culture (n\u2009=\u20093). f ALP (day 7) and ARS (day 14) staining with respective quantitative analyses in rBMSCs handled with remoted Mito\/MDVs (n\u2009=\u20093). Scale bars are as indicated. Knowledge signify imply\u2009\u00b1\u2009SD. *P\u2009<\u20090.05, **P\u2009<\u20090.01, and ***P\u2009<\u20090.001 by Pupil\u2019s t check (f)<\/p>\n<\/div>\n<\/div>\n<\/figure>\n<\/div>\n
DRP1 dephosphorylation at Ser656 drives donut-shaped mitochondrial transforming<\/h3>\n
To elucidate the exact molecular equipment driving the Pfkm-dependent mitochondrial morphological swap, we targeted on the genes or proteins that orchestrate organelle dynamics. Whereas mitochondrial fusion requires mitofusin 1\/2 (MFN1\/2) and optic atrophy 1 (OPA1), fission primarily is dependent upon dynamin-related protein 1 (DRP1) and its corresponding outer membrane receptors. We first examined each whole DRP1 expression and its site-specific phosphorylation standing. Though whole DRP1 ranges remained unchanged, Pfkm knockdown particularly triggered a considerable, site-specific lower in DRP1 phosphorylation on the Ser656 residue, whereas leaving the Ser635 website totally unaffected (Figs. 6a and S7a).<\/p>\n
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<\/div>\nPFKM regulates mitochondrial fission by way of DRP1 dephosphorylation at Ser656. a Western blot evaluation of p-DRP1 (Ser656) in siPfkm and siNC teams at 0, 1, 3, and 5\u2009h of osteogenesis (n\u2009=\u20093). b Confocal pictures (left) and fluorescence line profile (proper) of DRP1 (Inexperienced)-mitochondria (Pink) co-localization in siPfkm and siNC teams (n\u2009=\u20093). c Mitochondrial morphology in siPfkm-rBMSCs expressing the DRP1-S656D phosphomimetic mutant (n\u2009=\u20093). d Western blot evaluation of the secreted Mito\/MDVs from every group (n\u2009=\u20093). e ALP staining (day 7) and ARS staining (day 14) in siPfkm or siNC-rBMSCs expressing DRP1-WT or the DRP1-S656D phosphomimetic mutant (n\u2009=\u20093).Protein ranges of p-PKA substrate and p-PKA C (Thr197) (0, 1, 3 and 5\u2009h) in siPfkm-rBMSCs (f), and in Forskolin-treated siPfkm-rBMSCs at 3\u2009h (g) of osteogenesis. h Western blot evaluation of p-DRP1 (Ser656) in siPfkm cells with 10\u2009\u03bcmol\/L forskolin after 3\u2009h of osteogenesis (n\u2009=\u20093). Scale bars are as indicated<\/p>\n<\/div>\n<\/div>\n<\/figure>\n<\/div>\n
To find out how this particular dephosphorylation occasion influences DRP1 kinetics, we established cells stably expressing fluorescently tagged DRP1. Pfkm knockdown dramatically accelerated DRP1 translocation from the cytosol to mitochondria, as mirrored by considerably enhanced mitochondrial-DRP1 colocalization (Fig. 6b). To definitively check whether or not the phosphorylation state of Ser656 immediately dictates these structural shifts, we generated a phosphomimetic DRP1 variant (S656D-EGFP), substituting serine with aspartate to imitate constitutive phosphorylation (Fig. S7b, c). Remarkably, introducing the S656D mutation successfully blocked DRP1 recruitment to the organelle floor, suppressed the formation of donut-shaped mitochondria, and fully restored the interconnected tubular community that had been disrupted by Pfkm knockdown (Figs. 6c and S7d).<\/p>\n
We subsequent evaluated whether or not this DRP1-mediated transforming program is structurally tied to extracellular vesicle launch. Western blot evaluation of mitochondrial pellets remoted from tradition supernatants revealed that expressing the S656D mutant in Pfkm-knockdown cells considerably diminished extracellular ranges of COX IV and TOMM20, proving that Ser656 dephosphorylation-induced fission is important for the secretion of practical Mito\/MDVs (Fig. 6d). Moreover, introducing the S656D mutation into Pfkm-knockdown cells efficiently reversed the Pfkm knockdown-induced alterations by reducing each the elevated mtDNA copy numbers and the heightened mitophagy flux (Fig. S7e, f). Crucially, practical assays, together with ALP and ARS staining, subsequently confirmed that the S656D mutation partially suppressed the pro-osteogenic results of Pfkm knockdown (Figs. 6e and S7g).<\/p>\n
Lastly, we traced the upstream mechanism driving DRP1 dephosphorylation. Provided that protein kinase A (PKA) immediately phosphorylates DRP1 at Ser656,23,38 we measured PKA exercise in Pfkm-knockdown cells. As anticipated, Pfkm knockdown markedly lowered PKA exercise, however this was restored by the cyclic adenosine monophosphate (cAMP) activator forskolin (Fig. 6f, g). Concurrently, forskolin additionally reversed the DRP1 dephosphorylation at Ser656 attributable to Pfkm knockdown, establishing that Pfkm regulates DRP1 Ser656 phosphorylation by way of the PKA exercise (Fig. 6h).<\/p>\n
Enhanced MERCs formation drives calcium-dependent mitochondrial fission to advertise osteogenic differentiation<\/h3>\n
To unravel the molecular mechanisms underlying the improved osteogenic phenotype induced by Pfkm knockdown, we carried out RNA-seq evaluation. Phenotypic monitoring by way of ALP staining and exercise assays recognized day 3 of induction because the onset of serious divergence between the experimental and management teams (Fig. S8a). RNA-seq evaluation at this important time level revealed 795 differentially expressed genes between Pfkm-knockdown and management teams, amongst which Cd38 (ADPRC 1) emerged as one of the strongly upregulated genes (Fig. S8b). Persistently, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and Gene Set Enrichment Evaluation (GSEA) indicated a big enrichment within the calcium signaling pathway and calcium channel regulator actions, each of that are intently linked to CD38 operate (Fig. S8c, d). This sturdy upregulation was additional validated at each the mRNA and protein ranges by way of RT-qPCR and western blotting (Fig. S9a, b).<\/p>\n
To find out whether or not CD38 acts as the first practical bridge between PFKM and downstream phenotypes, we pharmacologically inhibited CD38. Notably, administration of a CD38 inhibitor considerably attenuated the pro-osteogenic results initially enhanced by Pfkm knockdown, as demonstrated by diminished ALP staining and exercise (Fig. S9c). Corroborating these practical shifts, mitochondrial morphology monitoring revealed that the donut-shaped morphology induced by Pfkm knockdown was largely restored to an interconnected reticular community upon CD38 inhibitor 1 therapy (Fig. S9d). This rescue was additional accompanied by restored PKA exercise and elevated Drp1 Ser656 phosphorylation (Fig. S9e, f). Collectively, these findings set up CD38 as a central downstream mediator coupling PFKM-directed metabolic signaling to mitochondrial structure and subsequent osteogenic dedication.<\/p>\n
To elucidate how CD38-mediated transforming of mitochondrial structure drives osteogenesis, we analyzed downstream Gene Ontology (GO) phrases. GO enrichment evaluation highlighted distinguished alterations in phrases associated to calcium ion binding, the endoplasmic reticulum (ER), and mitochondria (Fig. S10a). Pushed by these structural and organelle clues, we systematically examined key regulators of ER-mitochondria communication. Western blot evaluation demonstrated sustained elevation of CD38 and phosphodiesterase 1A (PDE1A) within the Pfkm-knockdown group all through osteogenesis (days 0, 3, 7, and 14) (Fig. S10b). In step with the above outcome, RT-qPCR confirmed upregulation of mRNA expression for genes related to ER and mitochondrial calcium channels, together with Ip3r1 (inositol 1,4,5-trisphosphate receptor kind 1), Pde1a, Cd38, Ryr1 (ryanodine receptor 1), Mcu (mitochondrial calcium uniporter), Micu1 (mitochondrial calcium uptake 1), and Vdac1 (voltage-dependent anion-selective channel 1), in addition to genes governing MERCs, akin to Esyt1 (prolonged synaptotagmin-like protein 1), Grp75 (glucose-regulated protein 75), and Pacs2 (phosphofurin acidic cluster sorting protein 2) (Fig. S10c).<\/p>\n
We subsequent sought to confirm whether or not this transcriptional program translated into bodily alterations on the organelle interface. Twin fluorescence probing of the ER and mitochondria demonstrated a considerably greater co-localization ratio within the knockdown group, indicating enhanced MERCs formation (Fig. 7a). To surpass the decision and diffraction limits of fluorescence microscopy, we employed TEM to exactly visualize the nanoscale hole of those contact websites (sometimes 10\u201350\u2009nm). TEM imaging confirmed a considerably narrowed inter-organelle distance (Fig. 7b) and an elevated frequency of MERC constructions in Pfkm-knockdown cells (Fig. 7c).<\/p>\n
![\"Fig.](\"https:\/\/media.springernature.com\/lw685\/springer-static\/image\/art%3A10.1038%2Fs41368-026-00460-5\/MediaObjects\/41368_2026_460_Fig7_HTML.png\")
<\/div>\nMERCs-mediated mitochondrial calcium inflow promotes osteogenesis in Pfkm-knockdown rBMSCs. a SIM pictures exhibiting the co-localization of mitochondria (Pink) and the ER(Inexperienced) in siPfkm and siNC teams at day 3 of osteogenic induction (n\u2009=\u20093). b TEM pictures (left) and quantitative evaluation (proper) of the gap between the ER and mitochondria in siPfkm and siNC teams after 3 days of osteogenic induction (n\u2009=\u20093). c TEM pictures (left) and quantification of MERCs (proper) in siPfkm and siNC teams after 3 days of osteogenic induction (n\u2009=\u20093). Mitochondrial Ca2+ dynamics assessed by Rhod-2AM (d) and quantification of peak fluorescence depth (e) throughout osteogenic induction (D0, D1, D3) (n\u2009=\u20096). f Western blot evaluation of phosphorylated DRP1 ranges in Pfkm-knockdown handled with MCU-i4 after 3\u2009h of osteogenic induction (n\u2009=\u20093). g ALP staining (day 7) and ARS staining (day 14) in siPfkm-rBMSCs handled with MCU-i4 (n\u2009=\u20093). Scale bars are as indicated. Knowledge signify imply\u2009\u00b1\u2009SD. *P\u2009<\u20090.05, **P\u2009<\u20090.01, and ***P\u2009<\u20090.001 by Pupil\u2019s t check (b, c, e)<\/p>\n<\/div>\n<\/div>\n<\/figure>\n<\/div>\n
Provided that MERCs function structural conduits for inter-organelle communication, we investigated whether or not this bodily enlargement facilitated enhanced ER-to-mitochondria Ca2+ switch. Utilizing Rhod-2 AM in a Ca2+-free medium, we monitored mitochondrial Ca2+ uptake and noticed that the knockdown group exhibited considerably amplified mitochondrial Ca2+ flux at days 0, 1, and three, peaking sharply at day 1 (Fig. 7d, e). To determine a direct causal hyperlink between this calcium inflow and downstream mitochondrial transforming, we sequentially blocked the pathway at two distinct regulatory nodes. Pharmacological inhibition of the upstream driver utilizing CD38 inhibitor 1, or the downstream channel utilizing the particular mitochondrial calcium uniporter inhibitor-MCU-i4, efficiently blunted the elevated mitochondrial Ca2+ flux induced by Pfkm knockdown (Fig. S11a, b).<\/p>\n
Crucially, MCU-i4 successfully reversed the Pfkm knockdown-induced dephosphorylation of DRP1 at Ser656 (Fig. 7f). In step with this biochemical rescue, MCU-i4 therapy lowered DRP1 recruitment to the mitochondria, efficiently restoring mitochondrial morphology from fragmented, donut-shaped constructions again to a tubular reticular community (Fig. S11c, d). Moreover, western blot evaluation revealed that MCU-i4 therapy additionally suppressed downstream mitophagy (Determine S11e). Lastly, practical assays by way of ALP and ARS staining demonstrated that MCU-i4 efficiently attenuated the pro-osteogenic phenotype triggered by Pfkm knockdown (Figs. 7g and S11f). Taken collectively, these information define an entire mechanistic cascade whereby Pfkm knockdown drives MERCs enlargement and Ca2+ inflow to set off DRP1-mediated fission and mitophagy, finally dictating osteogenic differentiation.<\/p>\n
The ERK\/c-Jun axis transcriptionally upregulates CD38 to drive mitochondrial transforming and osteogenic differentiation<\/h3>\n
To uncover the exact upstream molecular cascade by which Pfkm knockdown initiates Cd38 expression, we turned our consideration to transcriptional regulatory pathways. Earlier research have established that Cd38 transcription is regulated by way of practical Activator Protein 1 (AP-1) response components positioned inside its promoter area.39,40,41,42 Using the JASPAR database, we recognized putative AP-1 binding websites throughout the rat Cd38 promoter, the core sequences of that are evolutionarily conserved throughout people, mice, and rats (Fig. 8a). Provided that c-Jun is a significant practical subunit of the AP-1 complicated, we examined its activation standing to validate these predictions. Western blot evaluation revealed elevated phosphorylation of c-Jun, alongside elevated ERK1\/2 phosphorylation, in Pfkm-knockdown cells (Fig. 8b, c). To determine a direct causal hyperlink between this activated MAPK\/ERK signaling cascade and Cd38 transcription, cells have been handled with the selective ERK1\/2 inhibitor SCH772984. This pharmacological intervention considerably suppressed the Pfkm knockdown-induced upregulation of key downstream targets, together with p-c-Jun, CD38, PDE1A, and p-DRP1 (Fig. 8d). Consequently, SCH772984 efficiently rescued mitochondrial dynamics by restoring the reticular mitochondrial community and robustly lowering the recruitment of DRP1 to the mitochondria (Figs. 8e and S12). Western blot evaluation additional revealed that ERK1\/2 inhibition following Pfkm knockdown additionally suppressed downstream mitophagy (Fig. 8f). Persistently, practical assays confirmed that SCH772984 therapy attenuated the pro-osteogenic phenotype attributable to Pfkm knockdown, as evidenced by a considerable lower in ALP staining at day 7 and ARS-stained mineralized matrix at day 14 (Fig. 8g). Collectively, these findings exhibit that Pfkm knockdown upregulates CD38 expression by way of a twin mechanism involving c-Jun-mediated promoter activation and ERK1\/2-driven transcript stabilization, thereby driving downstream mitochondrial fission, mitophagy, and the pro-osteogenic phenotype.42<\/p>\n
![\"Fig.](\"https:\/\/media.springernature.com\/lw685\/springer-static\/image\/art%3A10.1038%2Fs41368-026-00460-5\/MediaObjects\/41368_2026_460_Fig8_HTML.png\")
<\/div>\nThe ERK\/c-Jun pathway mediates Pfkm knockdown-induced CD38 expression and osteogenic differentiation. a Motif enrichment evaluation figuring out transcription issue binding websites in CD38 promoter area. Western blot evaluation of signaling pathway in siPfkm and siNC teams throughout osteogenic induction (0, 1, 3, and 5\u2009h). Panels present the phosphorylation kinetics of c-Jun (b) and ERK (c), in addition to pathway-related protein expression within the presence of the inhibitor SCH772984 (0.1 and 0.2\u2009\u03bcmol\/L) (d) (n\u2009=\u20093). e Confocal pictures of mitochondrial morphology and quantification of mitochondrial facet ratio in siPfkm-rBMSCs handled with SCH772984 (0.1 and 0.2\u2009\u03bcmol\/L) throughout osteogenic induction (n\u2009=\u20093). f Western blot evaluation of TOMM20 and LC3B protein expression in siPfkm-rBMSCs handled with SCH772984 (0.1 and 0.2\u2009\u03bcmol\/L) after 3 days of osteogenic induction (n\u2009=\u20093). g ALP staining (day 7) and ARS staining (day 14), with corresponding quantitative analyses in siPfkm-rBMSCs following SCH772984 therapy (0.1 and 0.2\u2009\u03bcmol\/L) and osteogenic induction (n\u2009=\u20093). Scale bars are as indicated. Knowledge signify imply\u2009\u00b1\u2009SD. *P\u2009<\u20090.05, **P\u2009<\u20090.01, and ***P\u2009<\u20090.001 by one-way ANOVA with Dunnett\u2019s check vs. management (g)<\/p>\n<\/div>\n<\/div>\n<\/figure>\n<\/div>\n
AAV-mediated Pfkm suppression accelerates calvarial and femoral bone regeneration in vivo<\/h3>\n
To evaluate whether or not Pfkm knockdown may speed up bone restore underneath physiological situations, we utilized rat fashions that includes calvarial and femoral defects. Previous to evaluating bone therapeutic, we validated the in vivo effectivity of adeno-associated virus (AAV)-mediated gene suppression. 4 weeks post-injection, rBMSCs harvested from the handled animals confirmed a marked discount in PFKM protein ranges, establishing an optimum viral dosage of two.0\u2009\u00d7\u200910\u00b9\u00b9 viral genomes (vg) (Fig. S13a). Crucially, these ex vivo harvested cells absolutely recapitulated our prior in vitro mechanistic findings by exhibiting a fragmented, donut-shaped mitochondrial morphology (Fig. S13b), and displaying enhanced osteogenic capability, as evidenced by ALP staining and exercise (Fig. S13c).<\/p>\n
Having confirmed profitable gene knockdown and the next activation of this mitochondrial-osteogenic axis ex vivo, we subsequent evaluated the therapeutic efficacy of the intervention in vivo. Within the calvarial defect mannequin, rats obtained a neighborhood subcutaneous administration of AAV-shPfkm two weeks previous to surgical procedure, adopted by the implantation of a bilayer collagen membrane in the course of the operation to cowl the defects (Fig. S13d). Micro-CT evaluation at 4 weeks post-surgery revealed markedly enhanced bone regeneration within the AAV-shPfkm group, characterised by vital will increase in bone quantity fraction (BV\/TV), trabecular thickness (Tb.Th), and bone mineral density (BMD) (Figs. 9a and S13e). This radiological proof of accelerated bone formation velocity was additional supported by dynamic histomorphometry by way of sequential calcein labeling, which confirmed substantial elevations within the mineral apposition fee (MAR), bone formation fee per bone floor (BFR\/BS), and mineralizing floor per bone floor (MS\/BS) (Fig. S13f, g). These findings have been additional supported by histological evaluations: hematoxylin and eosin (H&E) and Masson staining confirmed extremely organized collagen deposition, and osteopontin (OPN) immunofluorescence confirmed sturdy osteogenic marker expression within the newly shaped tissue (Fig. 9b).<\/p>\n
![\"Fig.](\"https:\/\/media.springernature.com\/lw685\/springer-static\/image\/art%3A10.1038%2Fs41368-026-00460-5\/MediaObjects\/41368_2026_460_Fig9_HTML.png\")
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