Loss of p53 in mesenchymal stem cells promotes alteration of bone remodeling through negative regulation of osteoprotegerin

Cellular Senescence and Inflammaging in the Bone: Pathways, Genetics, Anti-Aging Strategies and Interventions

Advancing age is associated with several age-related diseases (ARDs), with musculoskeletal conditions impacting millions of elderly people worldwide. With orthopedic conditions contributing towards considerable number of patients, a deeper understanding of bone aging is the need of the hour. One of the underlying factors of bone aging is cellular senescence and its associated senescence associated secretory phenotype (SASP). SASP comprises of pro-inflammatory markers, cytokines and chemokines that arrest cell growth and development. The accumulation of SASP over several years leads to chronic low-grade inflammation with advancing age, also known as inflammaging. The pathways and molecular mechanisms focused on bone senescence and inflammaging are currently limited but are increasingly being explored. Most of the genes, pathways and mechanisms involved in senescence and inflammaging coincide with those associated with cancer and other ARDs like osteoarthritis (OA). Thus, exploring these pathways using techniques like sequencing, identifying these factors and combatting them with the most suitable approach are crucial for healthy aging and the early detection of ARDs. Several approaches can be used to aid regeneration and reduce senescence in the bone. These may be pharmacological, non-pharmacological and lifestyle interventions. With increasing evidence towards the intricate relationship between aging, senescence, inflammation and ARDs, these approaches may also be used as anti-aging strategies for the aging bone marrow (BM).

Cell signaling and transcriptional regulation of osteoblast lineage commitment, differentiation, bone formation, and homeostasis

The initiation of osteogenesis primarily occurs as mesenchymal stem cells undergo differentiation into osteoblasts. This differentiation process plays a crucial role in bone formation and homeostasis and is regulated by two intricate processes: cell signal transduction and transcriptional gene expression. Various essential cell signaling pathways, including Wnt, BMP, TGF-β, Hedgehog, PTH, FGF, Ephrin, Notch, Hippo, and Piezo1/2, play a critical role in facilitating osteoblast differentiation, bone formation, and bone homeostasis. Key transcriptional factors in this differentiation process include Runx2, Cbfβ, Runx1, Osterix, ATF4, SATB2, and TAZ/YAP. Furthermore, a diverse array of epigenetic factors also plays critical roles in osteoblast differentiation, bone formation, and homeostasis at the transcriptional level. This review provides an overview of the latest developments and current comprehension concerning the pathways of cell signaling, regulation of hormones, and transcriptional regulation of genes involved in the commitment and differentiation of osteoblast lineage, as well as in bone formation and maintenance of homeostasis. The paper also reviews epigenetic regulation of osteoblast differentiation via mechanisms, such as histone and DNA modifications. Additionally, we summarize the latest developments in osteoblast biology spurred by recent advancements in various modern technologies and bioinformatics. By synthesizing these insights into a comprehensive understanding of osteoblast differentiation, this review provides further clarification of the mechanisms underlying osteoblast lineage commitment, differentiation, and bone formation, and highlights potential new therapeutic applications for the treatment of bone diseases.

Vascular architecture regulates mesenchymal stromal cell heterogeneity via P53-PDGF signaling in the mouse incisor

Mesenchymal stem cells (MSCs) reside in niches to maintain tissue homeostasis and contribute to repair and regeneration. Although the physiological functions of blood and lymphatic vasculature are well studied, their regulation of MSCs as niche components remains largely unknown. Using adult mouse incisors as a model, we uncover the role of Trp53 in regulating vascular composition through THBS2 to maintain mesenchymal tissue homeostasis. Loss of Trp53 in GLI1+ progeny increases arteries and decreases other vessel types. Platelet-derived growth factors from arteries deposit in the MSC region and interact with PDGFRA and PDGFRB. Significantly, PDGFRA+ and PDGFRB+ cells differentially contribute to defined cell lineages in the adult mouse incisor. Collectively, our results highlight Trp53's importance in regulating the vascular niche for MSCs. They also shed light on how different arterial cells provide unique cues to regulate MSC subpopulations and maintain their heterogeneity. Furthermore, they provide mechanistic insight into MSC-vasculature crosstalk.

Osteoarthritis: Insights into Diagnosis, Pathophysiology, Therapeutic Avenues, and the Potential of Natural Extracts

Osteoarthritis (OA) stands as a prevalent and progressively debilitating clinical condition globally, impacting joint structures and leading to their gradual deterioration through inflammatory mechanisms. While both non-modifiable and modifiable factors contribute to its onset, numerous aspects of OA pathophysiology remain elusive despite considerable research strides. Presently, diagnosis heavily relies on clinician expertise and meticulous differential diagnosis to exclude other joint-affecting conditions. Therapeutic approaches for OA predominantly focus on patient education for self-management alongside tailored exercise regimens, often complemented by various pharmacological interventions primarily targeting pain alleviation. However, pharmacological treatments typically exhibit short-term efficacy and local and/or systemic side effects, with prosthetic surgery being the ultimate resolution in severe cases. Thus, exploring the potential integration or substitution of conventional drug therapies with natural compounds and extracts emerges as a promising frontier in enhancing OA management. These alternatives offer improved safety profiles and possess the potential to target specific dysregulated pathways implicated in OA pathogenesis, thereby presenting a holistic approach to address the condition's complexities.

Rutin promotes osteogenic differentiation of mesenchymal stem cells (MSCs) by increasing ECM deposition and inhibiting p53 expression

Mesenchymal stem cells (MSCs) are an important source of cells for bone regeneration. Although the utilization of MSCs along with growth factors and scaffolds is a beneficial clinical approach for bone tissue engineering, there is need for improvement on the effectiveness of MSC osteogenesis and differentiation. Rutin is a natural flavonoid and a major component for cell proliferation and bone development. However, studies on the mechanism through which rutin regulates osteogenesis and MSC differentiation are limited. Therefore, this study aimed to investigate the effect and mechanisms of rutin on osteogenic differentiation of MSCs. MSCs were extracted from umbilical cords and treated with rutin, followed by the examination of osteogenesis-related markers. Rutin treatment promoted the differentiation of MSCs towards the osteogenic lineage rather than the adipogenic lineage and increased the expression of osteogenic markers. RNA sequencing and bioinformatic analysis indicated that rutin regulated p53, a key gene in regulating the osteogenic differentiation of MSCs. Additionally, cellular experiments showed that rutin-induced decrease in p53 expression increased the formation of extracellular matrix (ECM) by promoting p65 phosphorylation and caspase-3 cleavage. Conclusively, this study demonstrates the importance of rutin in osteogenesis and indicates that rutin possesses potential pharmaceutical application for bone regeneration and bone tissue engineering.

Pharmacological and mechanistic aspects of quercetin in osteoporosis

Osteoporosis (OP) is a bone disease associated with increasing age. Currently, the most common medications used to treat OP are anabolic agents, anti-resorptive agents, and medications with other mechanisms of action. However, many of these medications have unfavorable adverse effects or are not intended for long-term use, potentially exerting a severe negative impact on a patient's life and career and placing a heavy burden on families and society. There is an urgent need to find new drugs that can replace these and have fewer adverse effects. Quercetin (Que) is a common flavonol in nature. Numerous studies have examined the therapeutic applications of Que. However, a comprehensive review of the anti-osteoporotic effects of Que has not yet been conducted. This review aimed to describe the recent studies on the anti-osteoporotic effects of Que, including its biological, pharmacological, pharmacokinetic, and toxicological properties. The outcomes demonstrated that Que could enhance OP by increasing osteoblast differentiation and activity and reducing osteoclast differentiation and activity via the pathways of Wnt/β-catenin, BMP/SMAD/RUNX2, OPG/RANKL/RANK, ERK/JNK, oxidative stress, apoptosis, and transcription factors. Thus, Que is a promising novel drug for the treatment of OP.

A Missense Variant in TP53 Could Be a Genetic Biomarker Associated with Bone Tissue Alterations

Metabolic bone diseases cover a broad spectrum of disorders that share alterations in bone metabolism that lead to a defective skeleton, which is associated with increasing morbidity, disability, and mortality. There is a close connection between the etiology of metabolic bone diseases and genetic factors, with TP53 being one of the genes associated therewith. The single nucleotide polymorphism (SNP) Arg72Pro of TP53 is a genetic factor associated with several pathologies, including cancer, stroke, and osteoporosis. Here, we aim to analyze the influence of the TP53 Arg72Pro SNP on bone mass in humanized Tp53 Arg72Pro knock-in mice. This work reports on the influence of the TP53 Arg72Pro polymorphism in bone microarchitecture, OPG expression, and apoptosis bone status. The results show that the proline variant of the TP53 Arg72Pro polymorphism (Pro72-p53) is associated with deteriorated bone tissue, lower OPG/RANK ratio, and lower apoptosis in bone tissue. In conclusion, the TP53 Arg72Pro polymorphism modulates bone microarchitecture and may be a genetic biomarker that can be used to identify individuals with an increased risk of suffering metabolic bone alterations.

3D bioprinting technology to construct bone reconstruction research model and its feasibility evaluation

Objective: To explore and construct a 3D bone remodeling research model displaying stability, repeatability, and precise simulation of the physiological and biochemical environment in vivo. Methods: In this study, 3D bioprinting was used to construct a bone reconstruction model. Sodium alginate (SA), hydroxyapatite (HA) and gelatin (Gel) were mixed into hydrogel as scaffold material. The osteoblast precursor cells MC3T3-E1 and osteoclast precursor cells RAW264.7 were used as seed cells, which may or may not be separated by polycarbonate membrane. The cytokines osteoprotegerin (OPG) and receptor activator of NF-κB ligand (RANKL) were used to induce cell differentiation. The function of scaffolds in the process of bone remodeling was analyzed by detecting the related markers of osteoblasts (alkaline phosphatase, ALP) and osteoclasts (tartrate resistant acid phosphatase, TRAP). Results: The scaffold showed good biocompatibility and low toxicity. The surface morphology aided cell adhesion and growth. The scaffold had optimum degradability, water absorption capacity and porosity, which are in line with the conditions of biological experiments. The effect of induced differentiation of cells was the best when cultured alone. After direct contact between the two types of cells at 2D or 3D level, the induced differentiation of cells was inhibited to varying degrees, although they still showed osteogenesis and osteoclast. After the cells were induced by indirect contact culture, the effect of induced differentiation improved when compared with direct contact culture, although it was still not as good as that of single culture. On the whole, the effect of inducing differentiation at 3D level was the same as that at 2D level, and its relative gene expression and enzyme activity were higher than that in the control group. Hence the scaffold used in this study could induce osteogenesis as well as osteoclast, thereby rendering it more effective in inducing new bone formation. Conclusion: This method can be used to construct the model of 3D bone remodeling mechanism.

Discovery of multipotent progenitor cells from human induced membrane: Equivalent to periosteum-derived stem cells in bone regeneration

Background

The periosteum stem cells (PSCs) plays a critical role in bone regeneration and defect reconstruction. Insertion of polymethyl methacrylate (PMMA) bone cement can form an induced membrane(IM) and showed promising strategy for bone defect reconstruction, the underlying mechanism remains unclear. Our study sought to determine whether IM-derived cells(IMDCs) versus PSCs have similar characteristics in bone regeneration.

Methods

IM and periosteum were harvested from ten bone defect patients treated with PMMA, the IMDCs and PSCs were isolated respectively. Morphological, functional and molecular evaluation was performed and matched for comparison.

Results

Both progenitor-like IMDCs and PSCs were successfully isolated. In vitro, we found IMDCs were similar to PSCs in morphology, colony forming capacity and expression of surface marker(CD90+, CD73+, CD105+, CD34-/CD45-). Meanwhile, these IMSCs displayed multipotency with chondrogenic, adipogenic and osteogenic differentiation, but differed in some IMSCs(3/10) population showing relatively poor osteogenic differentiation. The molecular profiles suggests that cell cycle and DNA replication signaling pathways were associated with these varying osteogenic potential. In vivo, we established a cell-based tissue-engineered bone by seeding IMDSs/PSCs to demineralized bone matrix (DBM) scaffold and demonstrated both IMDSs and PSCs enhanced bone regeneration in SCID mice bone defect model compared with DBM alone.

Conclusion

Our data demonstrated IM containing multipotent progenitor cells similar to that periosteum promoting bone regeneration, and indicated the existence of multiple subsets in osteogenic differentiation. Overall, the study provided a cellular and molecular insights in understanding the successful or failed outcome of bone defect healing.The translational potential of this article: This study confirmed IMDCs and PSCs share similar regeneration capacity and inform a translation potential of that cellular therapy applying IMDCs in bone defect repair.

The Molecular Regulatory Mechanism in Multipotency and Differentiation of Wharton's Jelly Stem Cells

Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) are isolated from Wharton's jelly tissue of umbilical cords. They possess the ability to differentiate into lineage cells of three germ layers. WJ-MSCs have robust proliferative ability and strong immune modulation capacity. They can be easily collected and there are no ethical problems associated with their use. Therefore, WJ-MSCs have great tissue engineering value and clinical application prospects. The identity and functions of WJ-MSCs are regulated by multiple interrelated regulatory mechanisms, including transcriptional regulation and epigenetic modifications. In this article, we summarize the latest research progress on the genetic/epigenetic regulation mechanisms and essential signaling pathways that play crucial roles in pluripotency and differentiation of WJ-MSCs.

Mdm2/p53 levels in bone marrow mesenchymal stromal cells are essential for maintaining the hematopoietic niche in response to DNA damage

Mesenchymal stromal cells (MSCs) are a key component of the bone marrow (BM) niche, providing essential support required for the maintenance of hematopoietic stem cells. To advance our understanding of physiological functions of p53 and Mdm2 in BM-MSCs, we developed traceable conditional mouse models targeting Mdm2 and/or Trp53 in vivo. We demonstrate that Mdm2 is essential for the emergence, maintenance, and hematopoietic support of BM-MSCs. Mdm2 haploinsufficiency in BM-MSCs resulted in genotoxic stress-associated thrombocytopenia, suggesting a functional role for Mdm2 in hematopoiesis. In a syngeneic mouse model of acute myeloid leukemia (AML), Trp53 deletion in BM-MSCs improved survival, and protected BM against hematopoietic toxicity from a murine Mdm2i, DS-5272. The transcriptional changes were associated with dysregulation of glycolysis, gluconeogenesis, and Hif-1α in BM-MSCs. Our results reveal a physiologic function of Mdm2 in BM-MSC, identify a previously unknown role of p53 pathway in BM-MSC-mediated support in AML and expand our understanding of the mechanism of hematopoietic toxicity of MDM2is.

Role of p53 in promoting BMP9‑induced osteogenic differentiation of mesenchymal stem cells through TGF‑β1

Known as a tumour suppressor gene, p53 also plays a key role in controlling the differentiation of mesenchymal stem cells (MSCs). Bone morphogenetic protein 9 (BMP9) has been identified as a potent factor in inducing osteogenic differentiation of MSCs, but its relationship with p53 remains unclear. The present study revealed that TP53 was expressed at higher levels in MSCs from patients with osteoporosis and was associated with the top 10 core central genes found in the current osteoporosis genetic screen. p53 was expressed in C2C12, C3H10T1/2, 3T3-L1, MEFs, and MG-63 cell lines, and could be upregulated by BMP9, as measured by western blotting and reverse-transcription quantitative PCR (RT-qPCR). Furthermore, overexpression of p53 increased the mRNA and protein levels of osteogenic marker Runx2 and osteopontin, as evaluated by western blotting and RT-qPCR in BMP9-induced MSCs, whereas the p53 inhibitor pifithrin (PFT)-α attenuated these effects. The same trend was found in alkaline phosphatase activities and matrix mineralization, as measured by alkaline phosphatase staining and alizarin red S staining. Moreover, p53 overexpression reduced adipo-differentiation markers of PPARγ and lipid droplet formation, as measured by western blotting, RT-qPCR and oil red O staining, respectively, whereas PFT-α facilitated adipo-differentiation in MSCs. In addition, p53 promoted TGF-β1 expression and inhibition of TGF-β1 by LY364947 partially attenuated the effects of p53 on promoting BMP9-induced MSC osteo-differentiation and inhibiting adipo-differentiation. The inhibitory effect of PFT-α on osteogenic markers and the promoting effect on adipogenic markers can be reversed when combined with TGF-β1. TGF-β1 may enhance the promotion of osteo-differentiation of MSCs by p53 through inhibition of adipo-differentiation. Collectively, by promoting BMP9-induced MSCs bone differentiation and inhibiting adipose differentiation, p53 may be a novel therapeutic target for bone-related diseases.

ZNF750: A Novel Prognostic Biomarker in Metastatic Prostate Cancer

Prostate cancer is the most frequently diagnosed cancer and the fifth leading cause of cancer death among men in 2020. The clinical decision making for prostate cancer patients is based on the stratification of the patients according to both clinical and pathological parameters such as Gleason score and prostate-specific antigen levels. However, these tools still do not adequately predict patient outcome. The aim of this study was to investigate whether ZNF750 could have a role in better stratifying patients, identifying those with a higher risk of metastasis and with the poorest prognosis. The data reported here revealed that ZNF750 protein levels are reduced in human prostate cancer samples, and this reduction is even higher in metastatic samples. Interestingly, nuclear positivity is significantly reduced in patients with metastatic prostate cancer, regardless of both Gleason score and grade group. More importantly, the bioinformatics analysis indicates that ZNF750 expression is positively correlated with better prognosis. Overall, our findings suggest that nuclear expression of ZNF750 may be a reliable prognostic biomarker for metastatic prostate cancer, which lays the foundation for the development of new biological therapies.

Mdm2/p53 levels in bone marrow mesenchymal stromal cells is essential for maintaining the hematopoietic niche in response to DNA damage

Mesenchymal stromal cells (MSCs) are a key component of the bone marrow (BM) niche, providing essential support required for maintenance of hematopoietic stem cells. To advance our understanding of physiological functions of p53 and Mdm2 in BM-MSCs, we developed traceable conditional mouse models targeting Mdm2 and/or Trp53 in vivo . We demonstrate that Mdm2 is essential for the emergence, maintenance and hematopoietic support of BM-MSCs. Mdm2 haploinsufficiency in BM-MSCs resulted in genotoxic stress-associated thrombocytopenia, suggesting a functional role for Mdm2 in hematopoiesis. In a syngeneic mouse model of acute myeloid leukemia (AML), Trp53 deletion in BM-MSCs improved survival, and protected BM against hematopoietic toxicity from a murine Mdm2i, DS-5272. The transcriptional changes were associated with dysregulation of glycolysis, gluconeogenesis, and Hif-1α in BM-MSCs. Our results reveal a physiologic function of Mdm2 in BM-MSC, identify a previously unknown role of p53 pathway in BM-MSC-mediated support in AML and expand our understanding of the mechanism of hematopoietic toxicity of MDM2is.

Electrically stimulated 3D bioprinting of gelatin-polypyrrole hydrogel with dynamic semi-IPN network induces osteogenesis via collective signaling and immunopolarization

In recent years, three-dimensional (3D) bioprinting of conductive hydrogels has made significant progress in the fabrication of high-resolution biomimetic structures with gradual complexity. However, the lack of an effective cross-linking strategy, ideal shear-thinning, appropriate yield strength, and higher print fidelity with excellent biofunctionality remains a challenge for developing cell-laden constructs, hindering the progress of extrusion-based 3D printing of conductive polymers. In this study, a highly stable and conductive bioink was developed based on polypyrrole-grafted gelatin methacryloyl (GelMA-PPy) with a triple cross-linking (thermo-photo-ionically) strategy for direct ink writing-based 3D printing applications. The triple-cross-linked hydrogel with dynamic semi-inner penetrating polymer network (semi-IPN) displayed excellent shear-thinning properties, with improved shape fidelity and structural stability during 3D printing. The as-fabricated hydrogel ink also exhibited "plug-like non-Newtonian" flow behavior with minimal disturbance. The bioprinted GelMA-PPy-Fe hydrogel showed higher cytocompatibility (93%) of human bone mesenchymal stem cells (hBMSCs) under microcurrent stimulation (250 mV/20 min/day). Moreover, the self-supporting and tunable mechanical properties of the GelMA-PPy bioink allowed 3D printing of high-resolution biological architectures. As a proof of concept, we printed a full-thickness rat bone model to demonstrate the structural stability. Transcriptomic analysis revealed that the 3D bioprinted hBMSCs highly expressed gene hallmarks for NOTCH/mitogen-activated protein kinase (MAPK)/SMAD signaling while down-regulating the Wnt/β-Catenin and epigenetic signaling pathways during osteogenic differentiation for up to 7 days. These results suggest that the developed GelMA-PPy bioink is highly stable and non-toxic to hBMSCs and can serve as a promising platform for bone tissue engineering applications.

The Role of procollagen type 1 amino-terminal propertied (P1NP) Cytochrome P450 (CYPs) and Osteoprotegerin (OPG) as Potential Bone function markers in Prostate Cancer Bone Metastasis

Background: Procollagen type I amino-terminal propeptide (PINP) is often present during osteoblast development and could be a biomarker of early bone development. Osteoprotegerin (OPG) may protect tumor cells from apoptosis. Cytochrome P450 enzymes help tumor development and treatment (CYPs). Cytochrome P450 activates and deactivates anticancer drugs and procarcinogens.

Objective: The study examined the amounts of a diagnostic marker of bone formation, the amino terminal propeptide of type I procollagen (PINP), Osteoprotegerin (OPG), and P450, in prostate cancer patients at different stages and its ability to detect osteoblastic metastases.

Methods: ELISA was used to measure PINP, OPG, and P450 levels in 30 prostate cancer patients. (n = 32) and healthy men’s serum (n = 36).

Results: Prostate cancer patients had higher blood levels of PINP, OPG, and P450 than healthy persons (301.3±134.9, 980±467.2, and 84.2±28.4 pg/mL, respectively). Compared to I+II prostate cancer patients, III+IV patients showed higher serum PINP, OPG, and P450 levels (P 0.001). OPG, P450, and PINP had statistically significant Area under the ROC curve (0.9467, P= 0.0001, 0.91, P= 0.0001, and 0.6977, P= 0.4035) in prostate cancer patients.

Conclusions: Metastatic prostate cancer patients had greater PINP, OPG, and P450 levels, according to our findings. PINP, OPG, and P450 levels may affect prostate cancer progression. These findings imply that serum PINP, OPG, and P450 levels may predict and diagnose prostate cancer.

Effects of legacy and emerging per- and polyfluoroalkyl substances on PPARα/β/γ regulation and osteogenic/adipogenic differentiation

As the primary molecular target, there is still a gap between the peroxisome proliferator-activated receptors (PPARs) regulation and the adverse health effects caused by per- and polyfluoroalkyl substances (PFASs). The effects of PFASs on cellular differentiation regulated by PPARs is likely significant given the association of PFASs exposure with obesity and decreased bone density. Human mesenchymal stem cells (hMSCs) were used as an in vitro model to assess the roles of PPAR subtypes in the multipotent differentiation of hMSCs affected by perfluorooctanesulfonate (PFOS), perfluorooctanoic acid (PFOA) and their replacement compounds. PFASs increased the expression of three PPAR subtypes in proliferating and differentiating hMSCs. Meanwhile, PFOS and PFOA decreased osteogenesis, enhanced adipogenesis, and increased bone turnover in hMSCs. Similarly, PFOA alternatives, hexafluoropropylene oxide dimer acid (HFPO-DA) and hexafluoropropylene oxide trimer acid (HFPO-TA), exhibited similar or even higher potency in affecting stem cell differentiation compared with PFOA. Perfluorohexanesulfonate (PFHxS) inhibited osteogenesis with comparable potency to PFOS. In contrast, 6:2 chlorinated poly-fluoroalkyl ether sulfonate (6:2Cl-PFESA) enhanced osteogenesis. PPARβ expression is significantly positively correlated with osteogenesis and osteoprotegerin (OPG) secretion in 6:2Cl-PFESA treated cells. shRNA knockdown of PPARβ remarkably reversed the osteogenic effects of 6:2Cl-PFESA and enhanced the adipogenic effects of the six chemicals. The results suggested that the adverse effects and relative potency of PFASs on the multipotent differentiation of hMSCs were dependent on the integrated action of the three PPAR subtypes, which facilitates a better understanding of the molecular initiating events of PFASs. The present study may well explain the mechanism of the decreased bone density and increased obesity incidence among those exposed to legacy PFASs, and indicates the necessity of further health risk assessment for the alternatives.

Rb1 negatively regulates bone formation and remodeling through inhibiting transcriptional regulation of YAP in Glut1 and OPG expression and glucose metabolism in male mice

OBJECTIVE

Bone is a highly dynamic organ that undergoes constant bone formation and remodeling, and glucose as a major nutrient is necessary for bone formation and remodeling. Retinoblastoma (Rb1) is a critical regulator of mesenchymal stem cells (MSCs) fate, but how Rb1 regulates bone formation and remodeling is poorly understood.

METHODS

We generated MSCs- and osteoprogenitors-specific Rb1 knockout mouse models and utilized these models to explore the function and mechanism of Rb1 in regulating bone formation and remodeling in vivo and in vitro primary cell culture.

RESULTS

Rb1 deficiency in MSCs significantly increased bone mass and impaired osteoclastogenesis. Consistently, depletion of Rb1 in osteoprogenitors significantly promoted bone formation. Mechanistically, loss of Rb1 in MSCs elevated YAP nuclear translocation and transcriptional activity of YAP/TEAD1 complex, thereby increasing the transcriptional expression of Glut1 and OPG. Moreover Prx1-Cre; Rb1f/f mice displayed hypoglycemia with increased systemic glucose tolerance instead of increased insulin level. In vitro data revealed that Rb1-mutant MSCs enhanced glucose uptake and lactate and ATP production. Increased osteogenesis caused by increased glucose metabolism and decreased osteoclastogenesis caused by increased expression of OPG eventually resulted in increased bone formation and remodeling.

CONCLUSIONS

Collectively, these findings demonstrated that Rb1 in MSCs inhibits YAP-medicated Glut1 and OPG expression to control glucose metabolism, osteogenesis and osteoclastogenesis during bone formation and remodeling, which provide new insights that controlling Rb1 signaling may be a potential strategy for osteopetrosis.

A Review of Signaling Transduction Mechanisms in Osteoclastogenesis Regulation by Autophagy, Inflammation, and Immunity

Osteoclastogenesis is an ongoing rigorous course that includes osteoclast precursors fusion and bone resorption executed by degradative enzymes. Osteoclastogenesis is controlled by endogenous signaling and/or regulators or affected by exogenous conditions and can also be controlled both internally and externally. More evidence indicates that autophagy, inflammation, and immunity are closely related to osteoclastogenesis and involve multiple intracellular organelles (e.g., lysosomes and autophagosomes) and certain inflammatory or immunological factors. Based on the literature on osteoclastogenesis induced by different regulatory aspects, emerging basic cross-studies have reported the emerging disquisitive orientation for osteoclast differentiation and function. In this review, we summarize the partial potential therapeutic targets for osteoclast differentiation and function, including the signaling pathways and various cellular processes.

Inhibition of RGS10 Aggravates Periapical Periodontitis via Upregulation of the NF-κB Pathway

INTRODUCTION

Periapical periodontitis develops due to the interplay between root canal microorganisms and host defenses. The mechanism underlying the pathogenesis of periapical periodontitis remains unclear. Regulator of G protein signaling protein 10 (RGS10) has been suggested to play a role in regulating inflammation. This study explored the potential regulatory effects of RGS10 on periapical periodontitis and the pro-inflammatory pathway of NF-κB.

METHODS

Disease models of periapical inflammation in mice were established, and adenovirus-associated virus (AAV) was used to inhibit RGS10 expression. Periapical lesions were detected using microcomputed tomography. Quantitative real-time PCR (qRT-PCR), western blotting (WB), enzyme-linked immunosorbent assay (ELISA), enzyme activity staining of tartrate-resistant acid phosphatase, and immunohistochemistry were conducted to assess the role of RGS10 expression on NF-κB pro-inflammatory signaling, OPG, RANKL, and osteoclasts in the periapical regions of each group. TNFα was used to stimulate L929 cells alone or with small interfering RNA (siRNA). To assess the expression of associated molecules, WB, immunofluorescence, qRT-PCR, and ELISA were performed.

RESULTS

RGS10 inhibition increased alveolar bone destruction in periapical periodontitis lesions and substantially enhanced the NF-κB pro-inflammatory signaling pathway activation level. Furthermore, RGS10 inhibition upregulated the ratio of OPG/RANKL and the maturation of osteoclasts during alveolar bone resorption. L929 cell TNFα stimulation and siRNA transfection confirmed these in vivo results.

CONCLUSION

RGS10 negatively regulates NF-κB pro-inflammatory signaling in periapical periodontitis and participates in bone remodeling. Therefore, RGS10 is a promising treatment option for long-term chronic periapical inflammation and may be a new target for the artificial regulation of inflammation.

Classifying Integrated Signature Molecules in Macrophages of Rheumatoid Arthritis, Osteoarthritis, and Periodontal Disease: An Omics-Based Study

Rheumatoid arthritis (RA), osteoarthritis (OA), and periodontal disease (PD) are chronic inflammatory diseases that are globally prevalent, and pose a public health concern. The search for a potential mechanism linking PD to RA and OA continues, as it could play a significant role in disease prevention and treatment. Recent studies have linked RA, OA, and PD to Porphyromonas gingivalis (PG), a periodontal bacterium, through a similar dysregulation in an inflammatory mechanism. This study aimed to identify potential gene signatures that could assist in early diagnosis as well as gain insight into the molecular mechanisms of these diseases. The expression data sets with the series IDs GSE97779, GSE123492, and GSE24897 for macrophages of RA, OA synovium, and PG stimulated macrophages (PG-SM), respectively, were retrieved and screened for differentially expressed genes (DEGs). The 72 common DEGs among RA, OA, and PG-SM were further subjected to gene–gene correlation analysis. A GeneMANIA interaction network of the 47 highly correlated DEGs comprises 53 nodes and 271 edges. Network centrality analysis identified 15 hub genes, 6 of which are DEGs (API5, ATE1, CCNG1, EHD1, RIN2, and STK39). Additionally, two significantly up-regulated non-hub genes (IER3 and RGS16) showed interactions with hub genes. Functional enrichment analysis of the genes showed that “apoptotic regulation” and “inflammasomes” were among the major pathways. These eight genes can serve as important signatures/targets, and provide new insights into the molecular mechanism of PG-induced RA, OA, and PD.

Trp53 controls chondrogenesis and endochondral ossification by negative regulation of TAZ activity and stability via β-TrCP-mediated ubiquitination

Transformation-related protein 53 (Trp53) is a critical regulator of cell fate determination by controlling cell proliferation and differentiation. Ablation of Trp53 signaling in osteoblast lineages significantly promotes osteogenesis, bone formation, and bone remodeling. However, how Trp53 regulates chondrogenesis and endochondral bone formation is undefined. In this study, we found that Trp53 expression gradually decreased in tibia growth plates during embryonic development in vivo and during chondrogenesis in vitro. By deleting Trp53 in chondrocyte lineage using Col2-Cre transgenic line, we found that loss of Trp53 in chondrocytes significantly increased growth plate growth and bone formation by increasing chondrocyte proliferation, matrix production and maturation, and bone dynamic formation rate. Mechanistically, our data revealed loss of Trp53 significantly promoted TAZ transcriptional activity through inhibition of TAZ phosphorylation and nuclear translocation, whereas its activity was pronouncedly inhibited after forced expression of Trp53. Furthermore, Co-IP data demonstrated that Trp53 associated with TAZ. Moreover, Trp53 decreased the stability of TAZ protein and promoted its degradation through β-TrCP-mediated ubiquitination. Ablation of TAZ in Col2-Cre;Trp53^f/f mice rescued the phenotypes of enhanced chondrogenesis and bone formation caused by Trp53 deletion. Collectively, this study revealed that Trp53 modulates chondrogenesis and endochondral ossification through negative regulation of TAZ activity and stability, suggesting that targeting Trp53 signaling may be a potential strategy for fracture healing, heterotopic ossification, arthritis, and other bone diseases.

Deletion of Trp53 and Rb1 in Ctsk-expressing cells drives osteosarcoma progression by activating glucose metabolism and YAP signaling

Glucose metabolism reprogramming is a critical factor in the progression of multiple cancers and is directly regulated by many tumor suppressors. However, how glucose metabolism regulates osteosarcoma development and progression is largely unknown. Cathepsin K (Ctsk) has been reported to express in chondroprogenitor cells and stem cells besides osteoclasts. Moreover, mutations in the tumor suppressors transformation-related protein 53 (Trp53) and retinoblastoma protein (Rb1) are evident in approximately 50%-70% of human osteosarcoma. To understand how deletion of Trp53 and Rb1 in Ctsk-expressing cells drives tumorigenesis, we generated the Ctsk-Cre;Trp53f/f/Rb1f/f mouse model. Our data revealed that those mice developed osteosarcoma without formation of tumor in osteoclast lineage. The level of cortical bone destruction was gradually increased in parallel to the osteosarcoma progression rate. Through mechanistic studies, we found that loss of Trp53/Rb1 in Ctsk-expressing cells significantly elevated Yes-associated protein (YAP) expression and activity. YAP/TEAD1 complex binds to the glucose transporter 1 (Glut1) promoter to upregulate Glut1 expression. Upregulated Glut1 expression led to overactive glucose metabolism, increasing osteosarcoma progression. Ablation of YAP signaling inhibited energy metabolism and delayed osteosarcoma progression in Ctsk-Cre;Trp53f/f/Rb1f/f mice. Collectively, these findings provide proof of principle that inhibition of YAP activity may be a potential strategy for osteosarcoma treatment.

The roles of osteoprotegerin in cancer, far beyond a bone player

Osteoprotegerin (OPG), also known as tumor necrosis factor receptor superfamily member 11B (TNFRSF11B), is a member of the tumor necrosis factor (TNF) receptor superfamily. Characterized by its ability to bind to receptor activator of nuclear factor kappa B ligand (RANKL), OPG is critically involved in bone remodeling. Emerging evidence implies that OPG is far beyond a bone-specific modulator, and is involved in multiple physiological and pathological processes, such as immunoregulation, vascular function, and fibrosis. Notably, numerous preclinical and clinical studies have been conducted to assess the participation of OPG in tumorigenesis and cancer development. Mechanistic studies have demonstrated that OPG is involved in multiple hallmarks of cancer, including tumor survival, epithelial to mesenchymal transition (EMT), neo-angiogenesis, invasion, and metastasis. In this review, we systematically summarize the basis and advances of OPG from its molecular structure to translational applications. In addition to its role in bone homeostasis, the physiological and pathological impacts of OPG on human health and its function in cancer progression are reviewed, providing a comprehensive understanding of OPG. We aim to draw more attention to OPG in the field of cancer, and to propose it as a promising diagnostic or prognostic biomarker as well as potential therapeutic target for cancer.

p53 deficiency promotes bone regeneration by functional regulation of mesenchymal stromal cells and osteoblasts

INTRODUCTION

The detailed mechanism of the process during bone healing of drill-hole injury has been elucidated, but a crucial factor in regulating drill-hole healing has not been identified. The transcription factor p53 suppresses osteoblast differentiation through inhibition of osterix expression. In present study, we demonstrate the effects of p53 deficiency on the capacity of MSCs and osteoblasts during drill-hole healing.

MATERIALS AND METHODS

Mesenchymal stromal cells (MSCs) and osteoblasts were collected from bone marrow and calvaria of p53 knockout (KO) mice, respectively. The activities of cell mobility, cell proliferation, osteoblast differentiation, and wound healing of MSCs and/or osteoblasts were determined by in vitro experiments. In addition, bone healing of drill-hole injury in KO mice was examined by micro-CT and immunohistological analysis using anti-osterix, Runx2, and sclerostin antibodies.

RESULTS

KO MSCs stimulated cell mobility, cell proliferation, and osteoblast differentiation. Likewise, KO osteoblasts enhanced cell proliferation and wound healing. KO MSCs and osteoblasts showed high potency in the inflammation and callus formation phases compared to those from wild-type (WT) mice. In addition, increased expression of osterix and Runx2 was observed in KO MSCs and osteoblasts that migrated in the drill-hole. Conversely, sclerostin expression was inhibited in KO mice. Eventually, KO mice exhibited high repairability of drill-hole injury, suggesting a novel role of p53 in MSCs and osteoblasts in improving bone healing.

CONCLUSION

p53 Deficiency promotes bone healing of drill-hole injury by enhancing the bone-regenerative ability of MSCs and osteoblasts.

A dual role of HIF1α in regulating osteogenesis–angiogenesis coupling

Objectives

The hypoxia-inducible factor 1-α (HIF1α), a key molecule in mediating bone-vessel crosstalk, has been considered a promising target for treating osteoporosis caused by gonadal hormones. However, senile osteoporosis, with accumulated senescent cells in aged bone, has a distinct pathogenesis. The study aimed at revealing the unknown role of HIF1α in aged bone, thus broadening its practical application in senile osteoporosis.

Materials and methods

Femurs and tibias were collected from untreated mice of various ages (2 months old, 10 months old, 18 months old) and treated mice (2 months old, 18 months old) underwent 4-w gavage of 2-methoxyestradiol (a kind of HIF1α inhibitor). Bone-vessel phenotypes were observed by microfil infusion, micro-CT and HE staining. Markers of senescence, osteogenesis, angiogenesis, oxidative stress and expression of HIF1α were detected by senescence β-galactosidase staining, qRT-PCR, western blot and immunostaining, respectively. Furthermore, bone mesenchymal stem cells from young mice (YBMSCs) and aged mice (ABMSCs) were transfected by knockout siRNA and overexpression plasmid of HIF1α. Senescence β-galactosidase staining, Cell Counting Kit-8, transwell assay, alkaline phosphatase staining, alizarin red-S staining and angiogenesis tests were utilized to assess the biological properties of two cell types. Then, Pifithrin-α and Nutlin-3a were adopted to intervene p53 of the two cells. Finally, H₂O₂ on YBMSCs and NAC on ABMSCs were exploited to change their status of oxidative stress to do a deeper detection.

Results

Senescent phenotypes, impaired osteogenesis–angiogenesis coupling and increased HIF1α were observed in aged bone and ABMSCs. However, 2-methoxyestradiol improved bone-vessel metabolism of aged mice while damaged that of young mice. Mechanically, HIF1α showed opposed effects in regulating the cell migration and osteogenesis–angiogenesis coupling of YBMSCs and ABMSCs, but no remarked effect on the proliferation of either cell type. Pifithrin-α upregulated the osteogenic and angiogenic markers of HIF1α-siRNA-transfected YBMSCs, and Nutlin-3a alleviated those of HIF1α-siRNA-transfected ABMSCs. The HIF1α-p53 relationship was negative in YBMSCs and NAC-treated ABMSCs, but positive in ABMSCs and H₂O₂-treated YBMSCs.

Conclusion

The dual role of HIF1α in osteogenesis–angiogenesis coupling may depend on the ROS-mediated HIF1α-p53 relationship. New awareness about HIF1α will be conducive to its future application in senile osteoporosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02742-1.

RIPK1 Coordinates Bone Marrow Mesenchymal Stem Cell Survival by Maintaining Mitochondrial Homeostasis via p53

Survival of mesenchymal stem cells in the bone marrow is essential for bone marrow microenvironment homeostasis, but the molecular mechanisms remain poorly understood. RIPK1 has emerged as a critical molecule of programmed cell death in tissue homeostasis. However, little is known about the regulation of RIPK1 on bone marrow mesenchymal stem cells (MSCs). Here, we have investigated for the first time the role of RIPK1 in bone marrow MSCs. We have found that RIPK1 knockdown suppressed proliferation, differentiation, and migration in bone marrow MSCs. Furthermore, RIPK1 knockdown resulted in the opening of mitochondrial permeability transition pore (mPTP) and mtDNA damage, leading to mitochondrial dysfunction, and consequently induced apoptosis and necroptosis in bone marrow MSCs. Moreover, we identified that the p53-PUMA axis pathway was involved in mitochondrial dysfunction in RIPK1-deficient bone marrow MSCs. Together, our findings highlighted that RIPK1 was indispensable for bone marrow MSC survival.

Osteoblast-specific inactivation of p53 results in locally increased bone formation

Inactivation of the tumor suppressor p53 (encoded by the Trp53 gene) is relevant for development and growth of different cancers, including osteosarcoma, a primary bone tumor mostly affecting children and young adolescents. We have previously shown that deficiency of the ribosomal S6 kinase 2 (Rsk2) limits osteosarcoma growth in a transgenic mouse model overexpressing the proto-oncogene c-Fos. Our initial aim for the present study was to address the question, if Rsk2 deficiency would also influence osteosarcoma growth in another mouse model. For that purpose, we took advantage of Trp53^fl/fl mice, which were crossed with Runx2^Cre transgenic mice in order to inactivate p53 specifically in osteoblast lineage cells. However, since we unexpectedly identified Runx2^Cre-mediated recombination also in the thymus, the majority of 6-month-old Trp53^{fl/fl;Runx2-Cre} (thereafter termed Trp53^Cre) animals displayed thymic lymphomas, similar to what has been described for Trp53-deficient mice. Since we did not detect osteosarcoma formation at that age, we could not follow our initial aim, but we studied the skeletal phenotype of Trp53^Cre mice, with or without additional Rsk2 deficiency. Here we unexpectedly observed that Trp53^Cre mice display a unique accumulation of trabecular bone in the midshaft region of the femur and the humerus, consistent with its previously established role as a negative regulator of osteoblastogenesis. Since this local bone mass increase in Trp53^Cre mice was significantly reduced by Rsk2 deficiency, we isolated bone marrow cells from the different groups of mice and analyzed their behavior ex vivo. Here we observed a remarkable increase of colony formation, osteogenic differentiation and proliferation in Trp53^Cre cultures, which was unaffected by Rsk2 deficiency. Our data thereby confirm a critical and tumorigenesis-independent function of p53 as a key regulator of mesenchymal cell differentiation.

Identification and preliminary validation of a four-gene signature to predict metastasis and survival in osteosarcoma

Osteosarcoma is a primary malignant bone tumor that occurs frequently in children and adolescents and has a propensity for drug resistance, recurrence, and metastasis. The purpose of this study was to identify potential target genes to predict metastasis and survival in patients with osteosarcoma. We analyzed gene expression profiles and corresponding clinical data of patients with osteosarcoma in the Gene Expression Omnibus database and identified 202 genes that were differentially expressed between osteosarcoma cells and normal osteoblasts. Univariate and multivariable Cox regression analyses identified four risk genes that affected osteosarcoma prognosis: MCAM, ENPEP, LRRC1, and CPE. Independent prognostic analyses and clinical correlation studies showed that the four risk genes constituted an independent prognostic signature that correlated with survival and clinical parameters including age and distant metastasis. In a single-sample Gene Set Enrichment Analysis, risk scores based on the prognostic signature correlated with tumor infiltration by immune cells and immune functions in osteosarcoma. A subsequent analysis showed that the expression levels of the four genes in the prognostic signature were predictive of overall survival and metastasis-free survival of patients with osteosarcoma. Furthermore, Human Cancer Metastasis Database and qRT-PCR analyses demonstrated that the four risk genes are overexpressed in osteosarcoma tissues and cell lines. In summary, we developed and validated a four-gene prognostic signature that may be useful in osteosarcoma diagnosis and metastasis prediction.

TAp63 regulates bone remodeling by modulating the expression of TNFRSF11B/Osteoprotegerin

ABBREVIATIONS

MSC, mesenchymal stem cells; OPG, osteoprotegerin; RUNX2, Run-trelated transcription factor 2.

The p53 family member p73 in the regulation of cell stress response

During oncogenesis, cells become unrestrictedly proliferative thereby altering the tissue homeostasis and resulting in subsequent hyperplasia. This process is paralleled by resumption of cell cycle, aberrant DNA repair and blunting the apoptotic program in response to DNA damage. In most human cancers these processes are associated with malfunctioning of tumor suppressor p53. Intriguingly, in some cases two other members of the p53 family of proteins, transcription factors p63 and p73, can compensate for loss of p53. Although both p63 and p73 can bind the same DNA sequences as p53 and their transcriptionally active isoforms are able to regulate the expression of p53-dependent genes, the strongest overlap with p53 functions was detected for p73. Surprisingly, unlike p53, the p73 is rarely lost or mutated in cancers. On the contrary, its inactive isoforms are often overexpressed in cancer. In this review, we discuss several lines of evidence that cancer cells develop various mechanisms to repress p73-mediated cell death. Moreover, p73 isoforms may promote cancer growth by enhancing an anti-oxidative response, the Warburg effect and by repressing senescence. Thus, we speculate that the role of p73 in tumorigenesis can be ambivalent and hence, requires new therapeutic strategies that would specifically repress the oncogenic functions of p73, while keeping its tumor suppressive properties intact.

Serine and one-carbon metabolisms bring new therapeutic venues in prostate cancer

Serine and one-carbon unit metabolisms are essential biochemical pathways implicated in fundamental cellular functions such as proliferation, biosynthesis of important anabolic precursors and in general for the availability of methyl groups. These two distinct but interacting pathways are now becoming crucial in cancer, the de novo cytosolic serine pathway and the mitochondrial one-carbon metabolism. Apart from their role in physiological conditions, such as epithelial proliferation, the serine metabolism alterations are associated to several highly neoplastic proliferative pathologies. Accordingly, prostate cancer shows a deep rearrangement of its metabolism, driven by the dependency from the androgenic stimulus. Several new experimental evidence describes the role of a few of the enzymes involved in the serine metabolism in prostate cancer pathogenesis. The aim of this study is to analyze gene and protein expression data publicly available from large cancer specimens dataset, in order to further dissect the potential role of the abovementioned metabolism in the complex reshaping of the anabolic environment in this kind of neoplasm. The data suggest a potential role as biomarkers as well as in cancer therapy for the genes (and enzymes) belonging to the one-carbon metabolism in the context of prostatic cancer.

Trophinin Is an Important Biomarker and Prognostic Factor in Osteosarcoma: Data Mining from Oncomine and the Cancer Genome Atlas Databases

Osteosarcoma (OS) is a type of bone malignancy with a high rate of treatment failure. To date, few evident biomarkers for the prognostic significance of OS have been established. Oncomine was used to integrate RNA and DNA-seq data from the Gene Expression Omnibus (GEO), The Cancer Genome Atlas (TCGA), and the published literature. The correlation of the gene Trophinin (TRO) and different types of cancers was generated using the Cancer Cell Line Encyclopedia (CCLE) online tool. Prognostic values of featured Melanoma Antigen Gene (MAGE) members were further assessed by establishing the overall survival using the Kaplan-Meier plotter. Moreover, the online tool, Database for Annotation, Visualization and Integrated Discovery version (DAVID), was used to understand the biological meaning list of the genes. MAGEB10, MAGED2, TRO, MAGEH1, MAGEB18, MAGEB6, MAGEB4, MAGEB1, MAGED4B, MAGED1, MAGEB2, and MAGEB3 were significantly overexpressed in sarcoma. TRO was further demonstrated to be distinctively upregulated in osteosarcoma cell lines and associated with shorter overall survival. TRO may play an important role in the development of OS and may be a promising potential biomarker and prognostic factor.

A Targeted Erythrocyte Membrane-Encapsulated Drug-Delivery System with Anti-osteosarcoma and Anti-osteolytic Effects

Chemotherapy is one of the main treatment methods for osteosarcoma. However, conventional chemotherapy lacks targeting properties, and its long-term and extensive use will have serious side effects on patients. For this reason, a multifunctional nanodrug system (V-RZCD) targeting osteosarcoma was developed in this study. V-RZCD consists of two parts: (1) the core (ZCD), wherein calcium ions (Ca2+) and zoledronic acid (ZA) form a metal-organic framework for loading doxorubicin (DOX), and (2) the shell (V-R), a vascular endothelial growth factor (VEGF) ligand-modified red blood cell membrane nanovesicle. By targeting the VEGF, V-RZCD can specifically bind to the VEGF receptors that are highly expressed on the surface of osteosarcoma cells. Importantly, compared with free ZA and DOX, V-RZCD not only clearly inhibits the proliferation of osteosarcoma but also significantly inhibits osteolysis induced by osteosarcoma. In summary, V-RZCD represents a new way to treat osteosarcoma.

18F-Sodium Fluoride PET as a Diagnostic Modality for Metabolic, Autoimmune, and Osteogenic Bone Disorders: Cellular Mechanisms and Clinical Applications

In a healthy body, homeostatic actions of osteoclasts and osteoblasts maintain the integrity of the skeletal system. When cellular activities of osteoclasts and osteoblasts become abnormal, pathological bone conditions, such as osteoporosis, can occur. Traditional imaging modalities, such as radiographs, are insensitive to the early cellular changes that precede gross pathological findings, often leading to delayed disease diagnoses and suboptimal therapeutic strategies. ¹⁸F-sodium fluoride (¹⁸F-NaF)-positron emission tomography (PET) is an emerging imaging modality with the potential for early diagnosis and monitoring of bone diseases through the detection of subtle metabolic changes. Specifically, the dissociated ¹⁸F^- is incorporated into hydroxyapatite, and its uptake reflects osteoblastic activity and bone perfusion, allowing for the quantification of bone turnover. While ¹⁸F-NaF-PET has traditionally been used to detect metastatic bone disease, recent literature corroborates the use of ¹⁸F-NaF-PET in benign osseous conditions as well. In this review, we discuss the cellular mechanisms of ¹⁸F-NaF-PET and examine recent findings on its clinical application in diverse metabolic, autoimmune, and osteogenic bone disorders.

Potential role of incretins in diabetes and COVID-19 infection: a hypothesis worth exploring

Patients with diabetes mellitus have been reported to be at a high risk of complications from SARS-CoV2 virus infection (COVID-19). In type 2 diabetes, there is a change in immune system cells, which shift from an anti-inflammatory to a predominantly pro-inflammatory pattern. This altered immune profile may induce important clinical consequences, including increased susceptibility to lung infections; and enhanced local inflammatory response. Furthermore, dipeptidyl peptidase 4 (DPP4) enzyme is highly expressed in the lung, and that it may have additional actions besides its effects on glucose metabolism, which might exert profound pro-inflammatory effects. We briefly review the impact on the inflammatory system of DPP4 for its possible detrimental effect on COVID-19 syndrome, and of DPP4 inhibitors (gliptins), currently used as glucose lowering agents, which may have the potential to exert positive pleiotropic effect on inflammatory diseases, in addition to their effects on glucose metabolism. Thanks to these ancillary effects, gliptins could potentially be "repurposed" as salutary drugs against COVID-19 syndrome, even in non-diabetic subjects. Clinical studies should be designed to investigate this possibility.