Lentiviral delivery of PPARγ shRNA alters the balance of osteogenesis and adipogenesis, improving bone microarchitecture

Knockdown of LAP2α inhibits adipogenesis of human adipose-derived stem cells and ameliorates high-fat diet-induced obesity

Adipogenesis, a pivotal cellular process involving the differentiation of mesenchymal stem cells (MSCs) to mature adipocytes, plays a significant role in various physiological functions. Dysregulation of adipogenesis is implicated in conditions such as obesity. However, the complete molecular understanding of adipogenesis remains elusive. This study aimed to uncover the novel role of lamina-associated polypeptide 2 alpha (LAP2α) in human adipose-derived stem cells (hASCs) adipogenesis and its impact on high-fat diet (HFD)-induced obesity and associated metabolic disturbances. LAP2α expression was assessed during the adipogenic differentiation of hASCs using RT-qPCR and western blotting. The functional role of LAP2α in adipogenesis was explored both in vitro and in vivo through loss- and gain-of-function studies. Moreover, mice with HFD-induced obesity received lentivirus injection to assess the effect of LAP2α knockdown on fat accumulation. Molecular mechanisms underlying LAP2α in adipogenic differentiation were investigated using RT-qPCR, Western blotting, immunofluorescence staining, and Oil Red O staining. LAP2α expression was upregulated during hASCs adipogenic differentiation. LAP2α knockdown hindered adipogenesis, while LAP2α overexpression promoted adipogenic differentiation. Notably, LAP2α deficiency resisted HFD-induced obesity, improved glucose intolerance, mitigated insulin resistance, and prevented fatty liver development. Mechanistically, LAP2α knockdown attenuated signal transducer and activator of transcription 3 (STAT3) activation by reducing the protein level of phosphorylated STAT3. A STAT3 activator (Colivelin) counteracted the negative impact of LAP2α deficiency on hASCs adipogenic differentiation. Taken together, our current study established LAP2α as a crucial regulator of hASCs adipogenic differentiation, unveiling a new therapeutic target for obesity prevention.

Arginine methylation of PPP1CA by CARM1 regulates glucose metabolism and affects osteogenic differentiation and osteoclastic differentiation

BACKGROUND

The imbalance between osteoblasts and osteoclasts may lead to osteoporosis. Osteoblasts and osteoclasts have different energy requirements, with aerobic glycolysis being the prominent metabolic feature of osteoblasts, while osteoclast differentiation and fusion are driven by oxidative phosphorylation.

METHODS

By polymerase chain reaction as well as Western blotting, we assayed coactivator-associated arginine methyltransferase 1 (CARM1) expression in bone tissue, the mouse precranial osteoblast cell line MC3T3-E1 and the mouse monocyte macrophage leukaemia cell line RAW264.7, and expression of related genes during osteogenic differentiation and osteoclast differentiation. Using gene overexpression (lentivirus) and loss-of-function approach (CRISPR/Cas9-mediated knockout) in vitro, we examined whether CARM1 regulates osteogenic differentiation and osteoblast differentiation by metabolic regulation. Transcriptomic assays and metabolomic assays were used to find the mechanism of action of CARM1. Furthermore, in vitro methylation assays were applied to clarify the arginine methylation site of PPP1CA by CARM1.

RESULTS

We discovered that CARM1 reprogrammed glucose metabolism in osteoblasts and osteoclasts from oxidative phosphorylation to aerobic glycolysis, thereby promoting osteogenic differentiation and inhibiting osteoclastic differentiation. In vivo experiments revealed that CARM1 significantly decreased bone loss in osteoporosis model mice. Mechanistically, CARM1 methylated R23 of PPP1CA, affected the dephosphorylation of AKT-T450 and AMPK-T172, and increased the activities of phosphofructokinase-1 and pructose-2,6-biphosphatase3, causing an up-regulation of glycolytic flux. At the same time, as a transcriptional coactivator, CARM1 regulated the expression of pyruvate dehydrogenase kinase 3, which resulted in the inhibition of pyruvate dehydrogenase activity and inhibition of the tricarboxylic acid cycle, leading to a subsequent decrease in the flux of oxidative phosphorylation.

CONCLUSIONS

These findings reveal for the first time the mechanism by which CARM1 affects both osteogenesis and osteoclast differentiation through metabolic regulation, which may represent a new feasible treatment strategy for osteoporosis.

WTAP-mediated m6A modification modulates bone marrow mesenchymal stem cells differentiation potential and osteoporosis

An imbalance in the differentiation potential of bone marrow mesenchymal stem cells (BMSCs) is an important pathogenic mechanism underlying osteoporosis (OP). N6-methyladenosine (m⁶A) is the most common post-transcriptional modification in eukaryotic cells. The role of the Wilms' tumor 1-associated protein (WTAP), a member of the m⁶A functional protein family, in regulating BMSCs differentiation remains unknown. We used patient-derived and mouse model-derived samples, qRT-PCR, western blot assays, ALP activity assay, ALP, and Alizarin Red staining to determine the changes in mRNA and protein levels of genes and proteins associated with BMSCs differentiation. Histological analysis and micro-CT were used to evaluate developmental changes in the bone. The results determined that WTAP promoted osteogenic differentiation and inhibited adipogenic differentiation of BMSCs. We used co-immunoprecipitation (co-IP), RNA immunoprecipitation (RIP), methylated RNA immunoprecipitation (MeRIP), RNA pulldown, and dual-luciferase assay to explore the direct mechanism. Mechanistically, the expression of WTAP increased during osteogenic differentiation and significantly promoted pri-miR-181a and pri-miR-181c methylation, which was recognized by YTHDC1, and increased the maturation to miR-181a and miR-181c. MiR-181a and miR-181c inhibited the mRNA expression of SFRP1, promoting the osteogenic differentiation of BMSCs. Our results demonstrated that the WTAP/YTHDC1/miR-181a and miR-181c/SFRP1 axis regulated the differentiation fate of BMSCs, suggesting that it might be a potential therapeutic target for osteoporosis.

Exercise-Linked Skeletal Irisin Ameliorates Diabetes-Associated Osteoporosis by Inhibiting the Oxidative Damage-Dependent miR-150-FNDC5/Pyroptosis Axis

Recent evidence suggests that physical exercise (EX) promotes skeletal development. However, the impact of EX on the progression of bone loss and deterioration of mechanical strength in mice with type 2 diabetic mellitus (T2DM) remains unexplored. In the current study, we investigated the effect of EX on bone mass and mechanical quality using a diabetic mouse model. The T2DM mouse model was established with a high-fat diet with two streptozotocin injections (50 mg/kg/body wt) in C57BL/6 female mice. The diabetic mice underwent treadmill exercises (5 days/week at 7-11 m/min for 60 min/day) for 8 weeks. The data showed that diabetes upregulated miR-150 expression through oxidative stress and suppressed FNDC5/Irisin by binding to its 3'-untranslated region. The decreased level of irisin further triggers the pyroptosis response in diabetic bone tissue. EX or N-acetyl cysteine or anti-miRNA-150 transfection in T2DM mice restored FNDC5/Irisin expression and bone formation. Furthermore, EX or recombinant irisin administration prevented T2DM-Induced hyperglycemia and improved glucose intolerance in diabetic mice. Furthermore, osteoblastic knockdown of Nlrp3 silencing (si-Nlrp3) or pyroptosis inhibitor (Ac-YVADCMK [AYC]) treatment restores bone mineralization in diabetic mice. Micro-computed tomography scans and mechanical testing revealed that trabecular bone microarchitecture and bone mechanical properties were improved after EX in diabetic mice. Irisin, either induced by skeleton or daily EX or directly administered, prevents bone loss by mitigating inflammasome-associated pyroptosis signaling in diabetic mice. This study demonstrates that EX-induced skeletal irisin ameliorates diabetes-associated glucose intolerance and bone loss and possibly provides a mechanism of its effects on metabolic osteoporosis.

Genetic and pharmacologic suppression of PPARγ enhances NELL-1-stimulated bone regeneration

Recent investigations into mechanisms behind the development of osteoporosis suggest that suppressing PPARγ-mediated adipogenesis can improve bone formation and bone mineral density. In this study, we investigated a co-treatment strategy to enhance bone formation by combining NELL-1, an osteogenic molecule that has been extensively studied for its potential use as a therapeutic for osteoporosis, with two methods of PPARγ suppression. First, we suppressed PPARγ genetically using lentiviral PPARγ-shRNA in immunocompromised mice for a proof of concept. Second, we used a PPARγ antagonist to suppress PPARγ pharmacologically in immunocompetent senile osteopenic mice for clinical transability. We found that the co-treatment strategy significantly increased bone formation, increased the proliferation stage cell population, decreased late apoptosis of primary mouse BMSCs, and increased osteogenic marker mRNA levels in comparison to the single agent treatment groups. The addition of PPARγ suppression to NELL-1 therapy enhanced NELL-1's effects on bone formation by upregulating anabolic processes without altering NELL-1's inhibitory effects on osteoclastic and adipogenic activities. Our findings suggest that combining PPARγ suppression with therapeutic NELL-1 may be a viable method that can be further developed as a novel strategy to reverse bone loss and decrease marrow adiposity in age-related osteoporosis.

GDF11 inhibits abnormal adipogenesis of condylar chondrocytes in temporomandibular joint osteoarthritis

Aims

Abnormal lipid metabolism is involved in the development of osteoarthritis (OA). Growth differentiation factor 11 (GDF11) is crucial in inhibiting the differentiation of bone marrow mesenchymal stem cells into adipocytes. However, whether GDF11 participates in the abnormal adipogenesis of chondrocytes in OA cartilage is still unclear.

Methods

Six-week-old female mice were subjected to unilateral anterior crossbite (UAC) to induce OA in the temporomandibular joint (TMJ). Histochemical staining, immunohistochemical staining (IHC), and quantitative real-time polymerase chain reaction (qRT-PCR) were performed. Primary condylar chondrocytes of rats were stimulated with fluid flow shear stress (FFSS) and collected for oil red staining, immunofluorescence staining, qRT-PCR, and immunoprecipitation analysis.

Results

Abnormal adipogenesis, characterized by increased expression of CCAAT/enhancer-binding protein α (CEBPα), fatty acid binding protein 4 (FABP4), Perilipin1, Adiponectin (AdipoQ), and peroxisome proliferator-activated receptor γ (PPARγ), was enhanced in the degenerative cartilage of TMJ OA in UAC mice, accompanied by decreased expression of GDF11. After FFSS stimulation, there were fat droplets in the cytoplasm of cultured cells with increased expression of PPARγ, CEBPα, FABP4, Perilipin1, and AdipoQ and decreased expression of GDF11. Exogenous GDF11 inhibited increased lipid droplets and expression of AdipoQ, CEBPα, and FABP4 induced by FFSS stimulation. GDF11 did not affect the change in PPARγ expression under FFSS, but promoted its post-translational modification by small ubiquitin-related modifier (SUMOylation). Local injection of GDF11 alleviated TMJ OA-related cartilage degeneration and abnormal adipogenesis in UAC mice.

Conclusion

Abnormal adipogenesis of chondrocytes and decreased GDF11 expression were observed in degenerative cartilage of TMJ OA. GDF11 supplementation effectively inhibits the adipogenesis of chondrocytes and thus alleviates TMJ condylar cartilage degeneration. GDF11 may inhibit the abnormal adipogenesis of chondrocytes by affecting the SUMOylation of PPARγ.

Cite this article: Bone Joint Res 2022;11(7):453–464.

Peroxisome Proliferator-Activated Receptor-γ Knockdown Impairs Bone Morphogenetic Protein-2-Induced Critical-Size Bone Defect Repair

The Food and Drug Administration-approved clinical dose (1.5 mg/mL) of bone morphogenetic protein-2 (BMP2) has been reported to induce significant adverse effects, including cyst-like adipose-infiltrated abnormal bone formation. These undesirable complications occur because of increased adipogenesis, at the expense of osteogenesis, through BMP2-mediated increases in the master regulatory gene for adipogenesis, peroxisome proliferator-activated receptor-γ (PPARγ). Inhibiting PPARγ during osteogenesis has been suggested to drive the differentiation of bone marrow stromal/stem cells toward an osteogenic, rather than an adipogenic, lineage. We demonstrate that knocking down PPARγ while concurrently administering BMP2 can reduce adipogenesis, but we found that it also impairs BMP2-induced osteogenesis and leads to bone nonunion in a mouse femoral segmental defect model. In addition, in vitro studies using the mouse bone marrow stromal cell line M2-10B4 and mouse primary bone marrow stromal cells confirmed that PPARγ knockdown inhibits BMP2-induced adipogenesis; attenuates BMP2-induced cell proliferation, migration, invasion, and osteogenesis; and escalates BMP2-induced cell apoptosis. More important, BMP receptor 2 and 1B expression was also significantly inhibited by the combined BMP2 and PPARγ knockdown treatment. These findings indicate that PPARγ is critical for BMP2-mediated osteogenesis during bone repair. Thus, uncoupling BMP2-mediated osteogenesis and adipogenesis using PPARγ inhibition to combat BMP2's adverse effects may not be feasible.

Frontal Bone Healing Is Sensitive to Wnt Signaling Inhibition via Lentiviral-Encoded Beta-Catenin Short Hairpin RNA

The Wnt/β-catenin signaling pathway plays an integral role in skeletal biology, spanning from embryonic skeletal patterning through bone maintenance and bone repair. Most experimental methods to antagonize Wnt signaling in vivo are either systemic or transient, including genetic approaches, use of small-molecule inhibitors, or neutralizing antibodies. We sought to develop a novel, localized model of prolonged Wnt/β-catenin signaling blockade by the application and validation of a lentivirus encoding β-catenin short hairpin RNA (shRNA). Efficacy of lentiviral-encoded β-catenin shRNA was first confirmed in vitro using bone marrow mesenchymal stromal cells, and in vivo using an intramedullary long bone injection model in NOD SCID mice. Next, the effects of β-catenin knockdown were assessed in a calvarial bone defect model, in which the frontal bone demonstrates enhanced bone healing associated with heightened Wnt/β-catenin signaling. Lentivirus encoding either β-catenin shRNA or random sequence shRNA with enhanced green fluorescent protein (control) was injected overlying the calvaria of NOD SCID mice and bone defects were created in either the frontal or parietal bones. Among mice treated with lentivirus encoding β-catenin shRNA, frontal bone defect healing was significantly reduced by all radiographic and histologic metrics. In contrast, parietal bone healing was minimally impacted by β-catenin shRNA. In aggregate, our data document the application and validation of a lentivirus encoding β-catenin shRNA model that represents an easily replicable tool for examining the importance of locoregional Wnt/β-catenin signaling in bone biology and regeneration.

Differential effects of bisphenol A diglicydyl ether on bone quality and marrow adiposity in ovary-intact and ovariectomized rats

Bisphenol A diglycidyl ether (BADGE), a PPARγ2 antagonist, has been shown to inhibit marrow adipogenesis and promote bone formation in intact animals. We investigated the impact of BADGE on a new and more clinically relevant physiological model, the ovariectomized (OVX) rat model. Forty female Wistar rats were divided into four treatment groups for 12 wk (n = 10/group): sham+vehicle, sham+BADGE, OVX+vehicle, and OVX+BADGE. Postmortem analyses included MRI, micro-CT, serological test, histomorphometry, biomechanical tests, RT-PCR, and Western blot. Overall, OVX induced a sequential marrow fat expansion accompanied by bone deterioration. Compared with OVX controls, BADGE reduced fat fraction of the distal femur by 36.3%, adipocyte density by 33.0%, adipocyte size by 28.6%, adipocyte volume percentage by 57.8%, and adipogenic markers PPARγ2 and C/EBPα by ∼50% in OVX rats. Similar results were observed in sham rats vs. vehicle. BADGE could promote bone quality in sham rats; however, BADGE did not significantly improve trabecular microarchitecture, biomechanical strength, and dynamic histomorphometric parameters except for trabecular separation in OVX rats. We concluded that early BADGE treatment at a dose of 30 mg/kg attenuates marrow adiposity in ovary-intact and OVX rats and stimulates bone formation in ovary-intact rats but does not significantly rescue bone quality in OVX rats.

Cultured Human Periosteum-Derived Cells Can Differentiate into Osteoblasts in a Perioxisome Proliferator-Activated Receptor Gamma-Mediated Fashion via Bone Morphogenetic Protein signaling

The differentiation of mesenchymal stem cells towards an osteoblastic fate depends on numerous signaling pathways, including activation of bone morphogenetic protein (BMP) signaling components. Commitment to osteogenesis is associated with activation of osteoblast-related signal transduction, whereas inactivation of this signal transduction favors adipogenesis. BMP signaling also has a critical role in the processes by which mesenchymal stem cells undergo commitment to the adipocyte lineage. In our previous study, we demonstrated that an agonist of the perioxisome proliferator-activated receptor γ (PPARγ), a master regulator of adipocyte differentiation, stimulates osteoblastic differentiation of cultured human periosteum-derived cells. In this study, we used dorsomorphin, a selective small molecule inhibitor of BMP signaling, to investigate whether BMP signaling is involved in the positive effects of PPARγ agonists on osteogenic phenotypes of cultured human periosteum-derived cells. Both histochemical detection and bioactivity of ALP were clearly increased in the periosteum-derived cells treated with the PPARγ agonist at day 10 of culture. Treatment with the PPARγ agonist also caused an increase in alizarin red S staining and calcium content in the periosteum-derived osteoblasts at 2 and 3 weeks of culture. In contrast, dorsomorphin markedly decreased ALP activity, alizarin red S staining and calcium content in both the cells treated with PPARγ agonist and the cells cultured in osteogenic induction media without PPARγ agonist during the culture period. In addition, the PPARγ agonist clearly increased osteogenic differentiation medium-induced BMP-2 upregulation in the periosteum-derived osteoblastic cells at 2 weeks of culture as determined by quantitative reverse transcriptase polymerase chain reaction (RT-PCR), immunoblotting, and immunocytochemical analyses. Although further study will be needed to clarify the mechanisms of PPARγ-regulated osteogenesis, our results suggest that the positive effects of a PPARγ agonist on the osteogenic phenotypes of cultured human periosteum-derived cells seem to be dependent on BMP signaling.

Irradiation alters the differentiation potential of bone marrow mesenchymal stem cells

Bone injury following radiotherapy has been confirmed by epidemiological and animal studies. However, the underlying mechanism remains to be elucidated and no preventive or curative solution has been identified for this bone loss. The present study aimed to investigate the irradiation‑altered osteogenesis and adipogenesis of bone marrow mesenchymal stem cells (BMSCs). BMSCs were derived and exposed to γ‑irradiation at doses of 0, 0.25, 0.5, 1, 2, 5 and 10 Gy. Cell viability was assessed using a 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5 diphenyl tetrazolium bromide assay, and clonal expansion in vitro was detected by colony forming unit assessment. The osteogenic differentiation ability was demonstrated by alkaline phosphatase (ALP) activity, ALP staining and mineralization alizarin red staining, and the adipogenic differentiation ability was determined using Oil O red staining. The osteogenesis‑associated genes, RUNX2, ALP, osteocalcin (OCN) and adipogenesis‑associated genes, PPAR‑γ and C/EBPα, were detected using reverse transcription‑quantitative polymerase chain reaction analyses. The protein expression levels of RUNX2, ALP and PPAR‑γ were detected using western blotting. Compared with the control, significant decreases in the proliferation, ALP activity and mineralization ability of the BMSCs were observed in the γ‑irradiation group, with a high level of correlation with the exposure dose. However, no significant changes were observed in the area of Oil red O positive staining. The mRNA levels of RUNX2, ALP and OCN were decreased (P<0.05), however, no significant changes were observed in the levels of C/EBPα and PPAR‑γ. The protein expression levels of RUNX2 and ALP were decreased in the irradiated BMSCs, however, no significant difference was observed in the protein expression of PPAR‑γ. Irradiation inhibited the osteogenic and adipogenic ability of the BMSCs, and the osteogenic differentiation was decreased. The results of the present study provided evidence to assist in further elucidating radiotherapy‑associated side effects on the skeleton.

FGF8 signaling sustains progenitor status and multipotency of cranial neural crest-derived mesenchymal cells in vivo and in vitro

The cranial neural crest (CNC) cells play a vital role in craniofacial development and regeneration. They are multi-potent progenitors, being able to differentiate into various types of tissues. Both pre-migratory and post-migratory CNC cells are plastic, taking on diverse fates by responding to different inductive signals. However, what sustains the multipotency of CNC cells and derivatives remains largely unknown. In this study, we present evidence that FGF8 signaling is able to sustain progenitor status and multipotency of CNC-derived mesenchymal cells both in vivo and in vitro. We show that augmented FGF8 signaling in pre-migratory CNC cells prevents cell differentiation and organogenesis in the craniofacial region by maintaining their progenitor status. CNC-derived mesenchymal cells with Fgf8 overexpression or control cells in the presence of exogenous FGF8 exhibit prolonged survival, proliferation, and multi-potent differentiation capability in cell cultures. Remarkably, exogenous FGF8 also sustains the capability of CNC-derived mesenchymal cells to participate in organogenesis such as odontogenesis. Furthermore, FGF8-mediated signaling strongly promotes adipogenesis but inhibits osteogenesis of CNC-derived mesenchymal cells in vitro. Our results reveal a specific role for FGF8 in the maintenance of progenitor status and in fate determination of CNC cells, implicating a potential application in expansion and fate manipulation of CNC-derived cells in stem cell-based craniofacial regeneration.

Running on time: the role of circadian clocks in the musculoskeletal system

The night and day cycle governs the circadian (24 hourly) rhythm of activity and rest in animals and humans. This is reflected in daily changes of the global gene expression pattern and metabolism, but also in the local physiology of various tissues. A central clock in the brain co-ordinates the rhythmic locomotion behaviour, as well as synchronizing various local oscillators, such as those found in the musculoskeletal system. It has become increasingly recognized that the internal molecular clocks in cells allow a tissue to anticipate the rhythmic changes in their local environment and the specific demands of that tissue. Consequently, the majority of the rhythmic clock controlled genes and pathways are tissue specific. The concept of the tissue-specific function of circadian clocks is further supported by the diverse musculoskeletal phenotypes in mice with deletions or mutations of various core clock components, ranging from increased bone mass, dwarfism, arthropathy, reduced muscle strength and tendon calcification. The present review summarizes the current understanding of the circadian clocks in muscle, bone, cartilage and tendon tissues, with particular focus on the evidence of circadian rhythms in tissue physiology, their entrainment mechanisms and disease links, and the tissue-specific clock target genes/pathways. Research in this area holds strong potential to advance our understanding of how circadian rhythms control the health and disease of the musculoskeletal tissues, which has major implications in diseases associated with advancing age. It could also have potential implications in sports performance and sports medicine.