Vangl2 limits chaperone-mediated autophagy to balance osteogenic differentiation in mesenchymal stem cells

RanGAP1 maintains chromosome stability in limb bud mesenchymal cells during bone development

BACKGROUND

Bone development involves the rapid proliferation and differentiation of osteogenic lineage cells, which makes accurate chromosomal segregation crucial for ensuring cell proliferation and maintaining chromosomal stability. However, the mechanism underlying the maintenance of chromosome stability during the rapid proliferation and differentiation of Prx1-expressing limb bud mesenchymal cells into osteoblastic precursor cells remains unexplored.

METHODS

A transgenic mouse model of RanGAP1 knockout of limb and head mesenchymal progenitor cells was constructed to explore the impact of RanGAP1 deletion on bone development by histomorphology and immunostaining. Subsequently, G-banding karyotyping analysis and immunofluorescence staining were used to examine the effects of RanGAP1 deficiency on chromosome instability. Finally, the effects of RanGAP1 deficiency on chromothripsis and bone development signaling pathways were elucidated by whole-genome sequencing, RNA-sequencing, and qPCR.

RESULTS

The ablation of RanGAP1 in limb and head mesenchymal progenitor cells expressing Prx1 in mice resulted in embryonic lethality, severe cartilage and bone dysplasia, and complete loss of cranial vault formation. Moreover, RanGAP1 loss inhibited chondrogenic or osteogenic differentiation of mesenchymal stem cells (MSCs). Most importantly, we found that RanGAP1 loss in limb bud mesenchymal cells triggered missegregation of chromosomes, resulting in chromothripsis of chromosomes 1q and 14q, further inhibiting the expression of key genes involved in multiple bone development signaling pathways such as WNT, Hedgehog, TGF-β/BMP, and PI3K/AKT in the chromothripsis regions, ultimately disrupting skeletal development.

CONCLUSIONS

Our results establish RanGAP1 as a critical regulator of bone development, as it supports this process by preserving chromosome stability in Prx1-expressing limb bud mesenchymal cells.

Stearoylation cycle regulates the cell surface distribution of the PCP protein Vangl2

Defects in planar cell polarity (PCP) have been implicated in diverse human pathologies. Vangl2 is one of the core PCP components crucial for PCP signaling. Dysregulation of Vangl2 has been associated with severe neural tube defects and cancers. However, how Vangl2 protein is regulated at the posttranslational level has not been well understood. Using chemical reporters of fatty acylation and biochemical validation, here we present that Vangl2 subcellular localization is regulated by a reversible S-stearoylation cycle. The dynamic process is mainly regulated by acyltransferase ZDHHC9 and deacylase acyl-protein thioesterase 1 (APT1). The stearoylation-deficient mutant of Vangl2 shows decreased plasma membrane localization, resulting in disruption of PCP establishment during cell migration. Genetically or pharmacologically inhibiting ZDHHC9 phenocopies the effects of the stearoylation loss of Vangl2. In addition, loss of Vangl2 stearoylation enhances the activation of oncogenic Yes-associated protein 1 (YAP), serine-threonine kinase AKT, and extracellular signal-regulated protein kinase (ERK) signaling and promotes breast cancer cell growth and HRas G12V mutant (HRasV12)-induced oncogenic transformation. Our results reveal a regulation mechanism of Vangl2, and provide mechanistic insight into how fatty acid metabolism and protein fatty acylation regulate PCP signaling and tumorigenesis by core PCP protein lipidation.

Biallelic loss-of-function variants of ZFTRAF1 cause neurodevelopmental disorder with microcephaly and hypotonia

PURPOSE

Neurodevelopmental disorders exhibit clinical and genetic heterogeneity, ergo manifest dysfunction in components of diverse cellular pathways; the precise pathomechanism for the majority remains elusive.

METHODS

We studied 5 affected individuals from 3 unrelated families manifesting global developmental delay, postnatal microcephaly, and hypotonia. We used exome sequencing and prioritized variants that were subsequently characterized using immunofluorescence, immunoblotting, pulldown assays, and RNA sequencing.

RESULTS

We identified biallelic variants in ZFTRAF1, encoding a protein of yet unknown function. Four affected individuals from 2 unrelated families segregated 2 homozygous frameshift variants in ZFTRAF1, whereas, in the third family, an intronic splice site variant was detected. We investigated ZFTRAF1 at the cellular level and signified it as a nucleocytoplasmic protein in different human cell lines. ZFTRAF1 was completely absent in the fibroblasts of 2 affected individuals. We also identified 110 interacting proteins enriched in mRNA processing and autophagy-related pathways. Based on profiling of autophagy markers, patient-derived fibroblasts show irregularities in the protein degradation process.

CONCLUSION

Thus, our findings suggest that biallelic variants of ZFTRAF1 cause a severe neurodevelopmental disorder.

Novel perspectives on autophagy-oxidative stress-inflammation axis in the orchestration of adipogenesis

Adipose tissue, an indispensable organ, fulfils the pivotal role of energy storage and metabolism and is instrumental in maintaining the dynamic equilibrium of energy and health of the organism. Adipocyte hypertrophy and adipocyte hyperplasia (adipogenesis) are the two primary mechanisms of fat deposition. Mature adipocytes are obtained by differentiating mesenchymal stem cells into preadipocytes and redifferentiation. However, the mechanisms orchestrating adipogenesis remain unclear. Autophagy, an alternative cell death pathway that sustains intracellular energy homeostasis through the degradation of cellular components, is implicated in regulating adipogenesis. Furthermore, adipose tissue functions as an endocrine organ, producing various cytokines, and certain inflammatory factors, in turn, modulate autophagy and adipogenesis. Additionally, autophagy influences intracellular redox homeostasis by regulating reactive oxygen species, which play pivotal roles in adipogenesis. There is a growing interest in exploring the involvement of autophagy, inflammation, and oxidative stress in adipogenesis. The present manuscript reviews the impact of autophagy, oxidative stress, and inflammation on the regulation of adipogenesis and, for the first time, discusses their interactions during adipogenesis. An integrated analysis of the role of autophagy, inflammation and oxidative stress will contribute to elucidating the mechanisms of adipogenesis and expediting the exploration of molecular targets for treating obesity-related metabolic disorders.

Regulation of mesenchymal stem cell differentiation by autophagy

Autophagy, a process that isolates intracellular components and fuses them with lysosomes for degradation, plays an important cytoprotective role by eliminating harmful intracellular substances and maintaining cellular homeostasis. Mesenchymal stem cells (MSCs) are multipotent progenitor cells with the capacity for self-renewal that can give rise to a subset of tissues and therefore have potential in regenerative medicine. However, a variety of variables influence the biological activity of MSCs following their proliferation and transplantation in vitro. The regulation of autophagy in MSCs represents a possible mechanism that influences MSC differentiation properties under the right microenvironment, affecting their regenerative and therapeutic potential. However, a deeper understanding of exactly how autophagy is mobilized to function as well as clarifying the mechanisms by which autophagy promotes MSCs differentiation is still needed. Here, we review the current literature on the complex link between MSCs differentiation and autophagy induced by various extracellular or intracellular stimuli and the molecular targets that influence MSCs lineage determination, which may highlight the potential regulation of autophagy on MSCs' therapeutic capacity, and provide a broader perspective on the clinical application of MSCs in the treatment of a wide range of diseases.

Targeting lysosomal quality control as a therapeutic strategy against aging and diseases

Previously, lysosomes were primarily referred to as the digestive organelles and recycling centers within cells. Recent discoveries have expanded the lysosomal functional scope and revealed their critical roles in nutrient sensing, epigenetic regulation, plasma membrane repair, lipid transport, ion homeostasis, and cellular stress response. Lysosomal dysfunction is also found to be associated with aging and several diseases. Therefore, function of macroautophagy, a lysosome-dependent intracellular degradation system, has been identified as one of the updated twelve hallmarks of aging. In this review, we begin by introducing the concept of lysosomal quality control (LQC), which is a cellular machinery that maintains the number, morphology, and function of lysosomes through different processes such as lysosomal biogenesis, reformation, fission, fusion, turnover, lysophagy, exocytosis, and membrane permeabilization and repair. Next, we summarize the results from studies reporting the association between LQC dysregulation and aging/various disorders. Subsequently, we explore the emerging therapeutic strategies that target distinct aspects of LQC for treating diseases and combatting aging. Lastly, we underscore the existing knowledge gap and propose potential avenues for future research.

Core planar cell polarity genes VANGL1 and VANGL2 in predisposition to congenital vertebral malformations

Congenital scoliosis (CS), affecting approximately 0.5 to 1 in 1,000 live births, is commonly caused by congenital vertebral malformations (CVMs) arising from aberrant somitogenesis or somite differentiation. While Wnt/ß-catenin signaling has been implicated in somite development, the function of Wnt/planar cell polarity (Wnt/PCP) signaling in this process remains unclear. Here, we investigated the role of Vangl1 and Vangl2 in vertebral development and found that their deletion causes vertebral anomalies resembling human CVMs. Analysis of exome sequencing data from multiethnic CS patients revealed a number of rare and deleterious variants in VANGL1 and VANGL2, many of which exhibited loss-of-function and dominant-negative effects. Zebrafish models confirmed the pathogenicity of these variants. Furthermore, we found that Vangl1 knock-in (p.R258H) mice exhibited vertebral malformations in a Vangl gene dose- and environment-dependent manner. Our findings highlight critical roles for PCP signaling in vertebral development and predisposition to CVMs in CS patients, providing insights into the molecular mechanisms underlying this disorder.

HMOX1 Participates in Pre-Eclampsia by Regulating the Proliferation, Apoptosis, and Angiogenesis Modulation Potential of Mesenchymal Stem Cells via VEGF

Mesenchymal stem cells (MSCs) are involved in the pathogenesis of pre-eclampsia (PE). Heme oxygenase (HMOX) protects against placental cytotoxic injuries associated with PE. Here, we aimed to clarify the roles of HMOX1 in MSC proliferation and apoptosis, trophoblast cell migration, and regulation of angiogenesis, and assess its involvement in the pathogenesis of PE. HMOX1 and vascular endothelial growth factor (VEGF) expression levels in decidual tissues and decidua-derived MSCs (dMSCs) of healthy pregnant women and patients with PE were evaluated via quantitative reverse transcription-polymerase chain reaction and western blotting. Moreover, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, flow cytometry, and transwell assays were used to analyze the cell viability, apoptosis, and migration, respectively. The tube formation ability of human umbilical vein endothelial cells (HUVECs) was also evaluated. Compared to the healthy pregnant women, HMOX1 expression was upregulated in the decidual tissue and downregulated in the dMSCs of patients with PE. HMOX1 overexpression significantly increased dMSC proliferation, decreased cell apoptosis, and increased VEGF expression. Moreover, HMOX1-plasmid transfected dMSC culture supernatant promoted the migration of HTR-8/SVneo cells and improved angiogenesis by HUVECs. The opposite effects were observed in HMOX1-small interfering RNA-treated dMSCs cells. However, VEGF-siRNA reversed the effects of HMOX1-plasmid. HMOX1 is involved in the pathogenesis of PE by regulating the proliferation, apoptosis, and angiogenesis modulation potential of MSCs via VEGF, acting as a potential therapeutic target for PE.

Loss of chaperone-mediated autophagy does not alter age-related bone loss in male mice

Chaperone-mediated autophagy (CMA) is a lysosome-dependent degradation pathway that eliminates proteins that are damaged, partially unfolded, or targeted for selective proteome remodeling. CMA contributes to several cellular processes, including stress response and proteostasis. Age-associated increase in cellular stressors and decrease in CMA contribute to pathologies associated with aging in various tissues. CMA contributes to bone homeostasis in young mice. An age-associated reduction in CMA was reported in osteoblast lineage cells; however, whether declining CMA contributes to skeletal aging is unknown. Herein we show that cellular stressors stimulate CMA in UAMS-32 osteoblastic cells. Moreover, the knockdown of an essential component of the CMA pathway, LAMP2A, sensitizes osteoblasts to cell death caused by DNA damage, ER stress, and oxidative stress. As elevations in these stressors are thought to contribute to age-related bone loss, we hypothesized that declining CMA contributes to the age-associated decline in bone formation by sensitizing osteoblast lineage cells to elevated stressors. To test this, we aged male CMA-deficient mice and controls up to 24 months of age and examined age-associated changes in bone mass and architecture. We showed that lack of CMA did not alter age-associated decline in bone mineral density as measured by dual x-ray absorptiometry (DXA). Moreover, microCT analysis performed at 24 months of age showed that vertebral cancellous bone volume, cortical thickness, and porosity of CMA-deficient and control mice were similar. Taken together, these results suggest that reduction of CMA does not contribute to age-related bone loss.

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.

Nuclear VANGL2 Inhibits Lactogenic Differentiation

Planar cell polarity (PCP) proteins coordinate tissue morphogenesis by governing cell patterning and polarity. Asymmetrically localized on the plasma membrane of cells, transmembrane PCP proteins are trafficked by endocytosis, suggesting they may have intracellular functions that are dependent or independent of their extracellular role, but whether these functions extend to transcriptional control remains unknown. Here, we show the nuclear localization of transmembrane, PCP protein, VANGL2, in the HCC1569 breast cancer cell line, and in undifferentiated, but not differentiated, HC11 cells that serve as a model for mammary lactogenic differentiation. The loss of Vangl2 function results in upregulation of pathways related to STAT5 signaling. We identify DNA binding sites and a nuclear localization signal in VANGL2, and use CUT&RUN to demonstrate recruitment of VANGL2 to specific DNA binding motifs, including one in the Stat5a promoter. Knockdown (KD) of Vangl2 in HC11 cells and primary mammary organoids results in upregulation of Stat5a, Ccnd1 and Csn2, larger acini and organoids, and precocious differentiation; phenotypes are rescued by overexpression of Vangl2, but not Vangl2ΔNLS. Together, these results advance a paradigm whereby PCP proteins coordinate tissue morphogenesis by keeping transcriptional programs governing differentiation in check.

Nuclear VANGL2 Inhibits Lactogenic Differentiation

Planar cell polarity (PCP) proteins coordinate tissue morphogenesis by governing cell patterning and polarity. Asymmetrically localized on the plasma membrane of cells, PCP proteins are also trafficked by endocytosis, suggesting they may have intracellular functions that are dependent or independent of their extracellular role, but whether these functions extend to transcriptional control remains unknown. Here, we show the nuclear localization of transmembrane, PCP protein, VANGL2, in undifferentiated, but not differentiated, HC11 cells, which serve as a model for mammary lactogenic differentiation. Loss of Vangl2 function results in upregulation of pathways related to STAT5 signaling. We identify DNA binding sites and a nuclear localization signal in VANGL2, and use CUT&RUN to demonstrate direct binding of VANGL2 to specific DNA binding motifs, including one in the Stat5a promoter. Knockdown (KD) of Vangl2 in HC11 cells and primary mammary organoids results in upregulation of Stat5a , Ccnd1 and Csn2 , larger acini and organoids, and precocious differentiation; phenotypes rescued by overexpression of Vangl2 , but not Vangl2 ΔNLS . Together, these results advance a paradigm whereby PCP proteins coordinate tissue morphogenesis by keeping transcriptional programs governing differentiation in check.

IGF2BP2-meidated m6A modification of CSF2 reprograms MSC to promote gastric cancer progression

The interaction between tumor cells and stromal cells within the tumor microenvironment plays a critical role in cancer progression. Mesenchymal stem cells (MSCs) are important tumor stromal cells that exhibit pro-oncogenic activities when reprogrammed by the tumor. However, the precise mechanisms underlying MSC reprogramming in gastric cancer remain not well understood. QRT-PCR, western blot, and immunohistochemistry were used to examine gene and protein expression levels. In vitro and in vivo experiments were conducted to assess the biological functions of gastric cancer cells. RNA-sequencing, RNA immunoprecipitation (RIP), and meRIP assays were performed to investigate underlying molecular mechanisms. We found a significant increase in the expression and N6-methyladenosine (m6A) modification levels of colony-stimulating factor 2 (CSF2) in gastric cancer MSCs. CSF2 gene overexpression induced the reprogramming of normal MSCs into cancer-promoting MSCs, thereby enhancing the proliferation, migration, and drug resistance of gastric cancer cells through the secretion of various pro-inflammatory factors. Additionally, we demonstrated that the m6A reader IGF2BP2 bound to and stabilized CSF2 mRNA in gastric cancer MSCs. Notably, overexpression of IGF2BP2 mimicked the effect of CSF2 on MSCs, promoting gastric cancer progression. Finally, we unveiled that CSF2 induced the ubiquitination of Notch1 to reprogram MSCs. Our study highlights a critical role of IGF2BP2-mediated m6A modification of CSF2 in reprogramming MSCs, which presents a promising therapeutic target for gastric cancer.

LAMP2A regulates the balance of mesenchymal stem cell adipo-osteogenesis via the Wnt/β-catenin/GSK3β signaling pathway

Chaperone-mediated autophagy (CMA) plays multiple roles in cell metabolism. We found that lysosome-associated membrane protein type 2A (LAMP2A), a crucial protein of CMA, plays a key role in the control of mesenchymal stem cell (MSC) adipo-osteogenesis. We identified a differentially expressed CMA gene (LAMP2) in GEO datasets (GSE4911 and GSE494). Further, we performed co-expression analyses to define the relationships between CMA components genes and other relevant genes including Col1a1, Runx2, Wnt3 and Gsk3β. Mouse BMSCs (mMSCs) exhibiting Lamp2a gene knockdown (LA-KD) and overexpression (LA-OE) were created using an adenovirus system; then we investigated LAMP2A function in vitro by Western blot, Oil Red staining, ALP staining, ARS staining and Immunofluorescence analysis. Next, we used a modified mouse model of tibial fracture to investigate LAMP2A function in vivo. LAMP2A knockdown in mMSCs decreased the levels of osteogenic-specific proteins (COL1A1 and RUNX2) and increased those of the adipogenesis markers PPARγ and C/EBPα; LAMP2A overexpression had the opposite effects. The active-β-catenin and phospho-GSK3β (Ser9) levels were upregulated by LAMP2A overexpression and downregulated by LAMP2A knockdown. In the mouse model of tibial fracture, mMSC-overexpressing LAMP2A improved bone healing, as demonstrated by microcomputed tomography and histological analyses. In summary, LAMP2A positively regulates mMSC osteogenesis and suppresses adipo-osteogenesis, probably via Wnt/β-catenin/GSK3β signaling. LAMP2A promoted fracture-healing in the mouse model of tibial fracture. KEY MESSAGES: • LAMP2 positively regulates the mBMSCs osteogenic differentiation. • LAMP2 negatively regulates the mBMSCs adipogenic differentiation. • LAMP2 regulates mBMSCs osteogenesis via Wnt/β-catenin/GSK3β signaling pathway. • LAMP2 overexpression mBMSCs promote the fracture healing.

VANGL2 inhibits antiviral IFN-I signaling by targeting TBK1 for autophagic degradation

Stringent control of type I interferon (IFN-I) signaling is critical to potent innate immune responses against viral infection, yet the underlying molecular mechanisms are still elusive. Here, we found that Van Gogh-like 2 (VANGL2) acts as an IFN-inducible negative feedback regulator to suppress IFN-I signaling during vesicular stomatitis virus (VSV) infection. Mechanistically, VANGL2 interacted with TBK1 and promoted the selective autophagic degradation of TBK1 via K48-linked polyubiquitination at Lys372 by the E3 ligase TRIP, which serves as a recognition signal for the cargo receptor OPTN. Furthermore, myeloid-specific deletion of VANGL2 in mice showed enhanced IFN-I production against VSV infection and improved survival. In general, these findings revealed a negative feedback loop of IFN-I signaling through the VANGL2-TRIP-TBK1-OPTN axis and highlighted the cross-talk between IFN-I and autophagy in preventing viral infection. VANGL2 could be a potential clinical therapeutic target for viral infectious diseases, including COVID-19.

Polystyrene microplastics arrest skeletal growth in puberty through accelerating osteoblast senescence

Polystyrene microplastics (PS-MPs) have attracted worldwide attention to their massive accumulation in terrestrial and aquatic ecosystems. It has been demonstrated that MPs are easily to accumulate in organs and exert toxic effects. However, their exposure risk to the skeleton remains unknown. In this study, we observed PS-MPs accumulation in both the long bones and axial bones, leading to reduced body length, as well as femur and tibia length. PS-MPs treated mice exhibited redundant skeletal growth and impaired trabecular bone micro-architecture, which is due to the suppressed osteogenic ability as the number of osteoblasts decreased significantly in PS-MPs treated mice. In histological analysis, we observed the accumulation of senescent osteoblasts in the bone trabecula of PS-MPs treated mice, as well as the impaired autophagy with decreased autophagosome and reduced autophagy-related proteins in the senescent osteoblasts. Re-establishing autophagy effectively reversed the senescent phenotype in osteoblasts and ameliorated PS-MPs induced skeletal growth arrest. Hence, our study reveals the detrimental role of PS-MPs in skeletal growth in puberty through accelerating osteoblast senescence, which may be alleviated by reactivating the autophagy. This study provides new evidence of the PS-MPs on health threats and the potential therapeutic targets to reverse it.

Osteogenic effects of rapamycin on bone marrow mesenchymal stem cells via inducing autophagy

BACKGROUND

While autophagy is essential for stem cells' self-renewal and differentiation, its effect on bone marrow mesenchymal stem cells (BMSCs) remains unclear. This study aimed to investigate the interaction between autophagy and osteogenic differentiation using rapamycin (RAPA), a classical autophagy agonist with osteo-regulatory effects.

METHODS

Rat BMSC's autophagy was analyzed after osteoinduction (0, 7, 14, and 21 d) by western blotting, immunofluorescence, and real-time quantitative polymerase chain reaction (RT-qPCR). In addition, we evaluated osteogenic differentiation using alizarin red staining, alkaline phosphatase assays, and RT-qPCR/Western blotting quantification of bone sialoprotein, type 1 collagen, alkaline phosphatase, osteopontin, and Runt-related transcription factor 2 mRNA and protein levels.

RESULTS

The BMSC's basal autophagy level gradually decreased during osteogenic differentiation with a decrease in BECN1 level and the lipidated (LC3-II) to unlipidated (LC3-I) microtubule-associated protein 1 light chain 3 ratio and an increase in the expression of selective autophagic target p62. In contrast, it increased with increasing RAPA concentration. Furthermore, while 2 nM RAPA promoted BMSC osteogenic differentiation on days 7 and 14, 5 nM RAPA inhibited osteogenesis on days 14 and 21. Inhibition of autophagy by the inhibitor 3-methyladenine could impair RAPA's osteogenesis-enhancing effect on BMSCs.

CONCLUSIONS

The BMSC's basal autophagy level decreased over time during osteogenic differentiation. However, an appropriate RAPA concentration promoted BMSC osteogenic differentiation via autophagy activation.

MYC promotes fibroblast osteogenesis by regulating ALP and BMP2 to participate in ectopic ossification of ankylosing spondylitis

BACKGROUND

Ectopic ossification is an important cause of disability in patients with ankylosing spondylitis (AS). Whether fibroblasts can transdifferentiate into osteoblasts and contribute to ossification remains unknown. This study aims to investigate the role of stem cell transcription factors (POU5F1, SOX2, KLF4, MYC, etc.) of fibroblasts in ectopic ossification in patients with AS.

METHODS

Primary fibroblasts were isolated from the ligaments of patients with AS or osteoarthritis (OA). In an in vitro study, primary fibroblasts were cultured in osteogenic differentiation medium (ODM) to induce ossification. The level of mineralization was assessed by mineralization assay. The mRNA and protein levels of stem cell transcription factors were measured by real-time quantitative PCR (q-PCR) and western blotting. MYC was knocked down by infecting primary fibroblasts with lentivirus. The interactions between stem cell transcription factors and osteogenic genes were analysed by chromatin immunoprecipitation (ChIP). Recombinant human cytokines were added to the osteogenic model in vitro to evaluate their role in ossification.

RESULTS

We found that MYC was elevated significantly in the process of inducing primary fibroblasts to differentiate into osteoblasts. In addition, the level of MYC was remarkably higher in AS ligaments than in OA ligaments. When MYC was knocked down, the expression of the osteogenic genes alkaline phosphatase (ALP) and bone morphogenic protein 2 (BMP2) was decreased, and the level of mineralization was reduced significantly. In addition, the ALP and BMP2 were confirmed to be the direct target genes of MYC. Furthermore, interferon-γ (IFN-γ), which showed high expression in AS ligaments, was found to promote the expression of MYC in fibroblasts in the process of ossification in vitro.

CONCLUSIONS

This study demonstrates the role of MYC in ectopic ossification. MYC may act as the critical bridge that links inflammation with ossification in AS, thus providing new insights into the molecular mechanisms of ectopic ossification in AS.

M1 macrophage-derived extracellular vesicle containing tsRNA-5006c promotes osteogenic differentiation of aortic valve interstitial cells through regulating mitophagy

Background

Osteogenic differentiation of aortic valve interstitial cells (AVICs) plays a key role in the calcific aortic valve disease progression. Extracellular vesicles (EVs)-derived from M1-polarized macrophages (M1-EVs) orchestrated intercellular communication by delivering non-coding RNAs such as tRNA-derived small RNAs (tsRNAs) is crucial for cardiovascular disease. However, the role and mechanism of M1-EVs tsRNAs in osteogenic differentiation of AVICs remains largely unclear.

Methods

M1-EVs and PBS treated-RAW 264.7 cell-derived EVs (NC-EVs) were incubated with AVICs and subjected to small RNA sequencing. Candidate tsRNA in M1-EVs was silenced to explore their effects on AVIC osteogenic differentiation and mitophagy.

Results

DiI-labeled M1-EVs were internalized by AVICs, resulting in significantly increased calcium nodule formation and expression of osteogenesis-related genes in AVICs, including RUNX2, BMP2, osteopontin, and SPP1, compared with NC-EVs. Small RNA sequencing revealed that 17 tsRNAs were significantly up-regulated such as tsRNA-5006c, while 28 tsRNAs were significantly down-regulated in M1-EVs compared with NC-EVs. Intriguingly, tsRNA-5006c-deleted M1-EVs treatment significantly reduced calcium nodule formation and expression of osteogenesis-related genes in AVICs relative to control group. Moreover, target genes of tsRNA-5006c were mainly involved in autophagy-related signaling pathways, such as MAPK, Ras, Wnt, and Hippo signaling pathway. Hallmarks of mitophagy activation in AVICs including mitophagosome formation, TMRM fluorescence, expression of LC3-II, BINP3, and PGC1α, were significantly elevated in the M1-EVs group compared with NC-EVs group, whereas M1-EVs tsRNA-5006c inhibitor led to a significant reduction in these indicators.

Conclusion

M1-EVs carried tsRNA-5006c regulates AVIC osteogenic differentiation from the perspective of mitophagy, and we provide a new target for the prevention and treatment of aortic valve calcification.

Autophagy: An important target for natural products in the treatment of bone metabolic diseases

Bone homeostasis depends on a precise dynamic balance between bone resorption and bone formation, involving a series of complex and highly regulated steps. Any imbalance in this process can cause disturbances in bone metabolism and lead to the development of many associated bone diseases. Autophagy, one of the fundamental pathways for the degradation and recycling of proteins and organelles, is a fundamental process that regulates cellular and organismal homeostasis. Importantly, basic levels of autophagy are present in all types of bone-associated cells. Due to the cyclic nature of autophagy and the ongoing bone metabolism processes, autophagy is considered a new participant in bone maintenance. Novel therapeutic targets have emerged as a result of new mechanisms, and bone metabolism can be controlled by interfering with autophagy by focusing on certain regulatory molecules in autophagy. In parallel, several studies have reported that various natural products exhibit a good potential to mediate autophagy for the treatment of metabolic bone diseases. Therefore, we briefly described the process of autophagy, emphasizing its function in different cell types involved in bone development and metabolism (including bone marrow mesenchymal stem cells, osteoblasts, osteocytes, chondrocytes, and osteoclasts), and also summarized research advances in natural product-mediated autophagy for the treatment of metabolic bone disease caused by dysfunction of these cells (including osteoporosis, rheumatoid joints, osteoarthritis, fracture nonunion/delayed union). The objective of the study was to identify the function that autophagy serves in metabolic bone disease and the effects, potential, and challenges of natural products for the treatment of these diseases by targeting autophagy.

Role of Chaperone-Mediated Autophagy in Ageing Biology and Rejuvenation of Stem Cells

What lies at the basis of the mechanisms that regulate the maintenance and self-renewal of pluripotent stem cells is still an open question. The control of stemness derives from a fine regulation between transcriptional and metabolic factors. In the last years, an emerging topic has concerned the involvement of Chaperone-Mediated Autophagy (CMA) as a key mechanism in stem cell pluripotency control acting as a bridge between epigenetic, transcriptional and differentiation regulation. This review aims to clarify this new and not yet well-explored horizon discussing the recent studies regarding the CMA impact on embryonic, mesenchymal, and haematopoietic stem cells. The review will discuss how CMA influences embryonic stem cell activity promoting self-renewal or differentiation, its involvement in maintaining haematopoietic stem cell function by increasing their functionality during the normal ageing process and its effects on mesenchymal stem cells, in which modulation of CMA regulates immunosuppressive and differentiation properties. Finally, the importance of these new discoveries and their relevance for regenerative medicine applications, from transplantation to cell rejuvenation, will be addressed.

Vangl as a Master Scaffold for Wnt/Planar Cell Polarity Signaling in Development and Disease

The establishment of polarity within tissues and dynamic cellular morphogenetic events are features common to both developing and adult tissues, and breakdown of these programs is associated with diverse human diseases. Wnt/Planar cell polarity (Wnt/PCP) signaling, a branch of non-canonical Wnt signaling, is critical to the establishment and maintenance of polarity in epithelial tissues as well as cell motility events critical to proper embryonic development. In epithelial tissues, Wnt/PCP-mediated planar polarity relies upon the asymmetric distribution of core proteins to establish polarity, but the requirement for this distribution in Wnt/PCP-mediated cell motility remains unclear. However, in both polarized tissues and migratory cells, the Wnt/PCP-specific transmembrane protein Vangl is required and appears to serve as a scaffold upon which the core pathway components as well as positive and negative regulators of Wnt/PCP signaling assemble. The current literature suggests that the multiple interaction domains of Vangl allow for the binding of diverse signaling partners for the establishment of context- and tissue-specific complexes. In this review we discuss the role of Vangl as a master scaffold for Wnt/PCP signaling in epithelial tissue polarity and cellular motility events in developing and adult tissues, and address how these programs are dysregulated in human disease.

Regulation of microtubule dynamics, mechanics and function through the growing tip

Microtubule dynamics and their control are essential for the normal function and division of all eukaryotic cells. This plethora of functions is, in large part, supported by dynamic microtubule tips, which can bind to various intracellular targets, generate mechanical forces and couple with actin microfilaments. Here, we review progress in the understanding of microtubule assembly and dynamics, focusing on new information about the structure of microtubule tips. First, we discuss evidence for the widely accepted GTP cap model of microtubule dynamics. Next, we address microtubule dynamic instability in the context of structural information about assembly intermediates at microtubule tips. Three currently discussed models of microtubule assembly and dynamics are reviewed. These are considered in the context of established facts and recent data, which suggest that some long-held views must be re-evaluated. Finally, we review structural observations about the tips of microtubules in cells and describe their implications for understanding the mechanisms of microtubule regulation by associated proteins, by mechanical forces and by microtubule-targeting drugs, prominently including cancer chemotherapeutics.