Gli1+ Cells Couple with Type H Vessels and Are Required for Type H Vessel Formation

Gli1-mediated tumor cell-derived bFGF promotes tumor angiogenesis and pericyte coverage in non-small cell lung cancer

BACKGROUND

Tumor angiogenesis inhibitors have been applied for non-small cell lung cancer (NSCLC) therapy. However, the drug resistance hinders their further development. Intercellular crosstalk between lung cancer cells and vascular cells was crucial for anti-angiogenenic resistance (AAD). However, the understanding of this crosstalk is still rudimentary. Our previous study showed that Glioma-associated oncogene 1 (Gli1) is a driver of NSCLC metastasis, but its role in lung cancer cell-vascular cell crosstalk remains unclear.

METHODS

Conditioned medium (CM) from Gli1-overexpressing or Gli1-knockdown NSCLC cells was used to educate endothelia cells and pericytes, and the effects of these media on angiogenesis and the maturation of new blood vessels were evaluated via wound healing assays, Transwell migration and invasion assays, tube formation assays and 3D coculture assays. The xenograft model was conducted to establish the effect of Gli1 on tumor angiogenesis and growth. Angiogenic antibody microarray analysis, ELISA, luciferase reporte, chromatin immunoprecipitation (ChIP), bFGF protein stability and ubiquitination assay were performed to explore how Gli1 regulate bFGF expression.

RESULTS

Gli1 overexpression in NSCLC cells enhanced the endothelial cell and pericyte motility required for angiogenesis required for angiogenesis. However, Gli1 knockout in NSCLC cells had opposite effect on this process. bFGF was critical for the enhancement effect on tumor angiogenesis. bFGF treatment reversed the Gli1 knockdown-mediated inhibition of angiogenesis. Mechanistically, Gli1 increased the bFGF protein level by promoting bFGF transcriptional activity and protein stability. Importantly, suppressing Gli1 with GANT-61 obviously inhibited angiogenesis.

CONCLUSION

The Gli1-bFGF axis is crucial for the crosstalk between lung cancer cells and vascular cells. Targeting Gli1 is a potential therapeutic approach for NSCLC angiogenesis.

YBX1 promotes type H vessel-dependent bone formation in an m5C-dependent manner

RNA-binding proteins (RBPs) interact with RNA and ubiquitously regulate RNA transcripts during their life cycle, playing a fundamental role in the progression of angiogenesis-related diseases. In the skeletal system, endothelium-dependent angiogenesis is indispensable for bone formation. However, the role of RBPs in endothelium-dependent bone formation is unclear. Here, we show that RBP-Y-box-binding protein 1 (YBX1) was strongly reduced in the bone vasculature of ovariectomy (OVX) mice. Endothelial cell-specific deletion of Ybx1 impaired CD31-high, endomucin-high (CD31hiEMCNhi) endothelium morphology and resulted in low bone mass whereas Ybx1 overexpression promoted angiogenesis-dependent osteogenesis and ameliorated bone loss. Mechanistically, YBX1 deletion disrupted CD31, EMCN, and bone morphogenetic protein 4 (BMP4) stability in an m5C-dependent manner and blocked endothelium-derived BMP4 release, thereby inhibiting osteogenic differentiation of bone mesenchymal stromal cells. Administration of recombinant BMP4 protein restored impaired bone formation in Ybx1 deletion mice. Tail vein injection of CD31-modified polyethylene glycol-poly (lactic-co-glycolic acid) carrying sciadopitysin, a natural YBX1 agonist, pharmacologically partially reversed CD31hiEMCNhi vessels' decline and improved bone mass in both OVX and aging animals. These findings demonstrated the role of RBP-YBX1 in angiogenesis-dependent bone formation and provided a therapeutic approach for ameliorating osteoporosis.

Mesenchymal Stem Cell-Derived Exosomes in Various Chronic Liver Diseases: Hype or Hope?

Chronic liver conditions are associated with high mortality rates and have a large adverse effect on human well-being as well as a significant financial burden. Currently, the only effective treatment available for the effects of liver failure and cirrhosis resulting from the progression of several chronic liver diseases is liver transplantation carried out at the original location. This implies that developing novel and effective treatments is imperative. Regenerative medicine has long been associated with stem cell therapy. Mesenchymal stem cells (MSCs), a type of cell with great differentiation potential, have become the preferred source for stem cell therapy. According to recent studies, MSCs' paracrine products-rather than their capacity for differentiation-play a significant therapeutic effect. MSC exosomes, a type of extracellular vesicle (MSC-EV), came into view as the paracrine substances of MSCs. According to research, MSC exosomes can maintain tissue homeostasis, which is necessary for healthy tissue function. All tissues contain them, and they take part in a variety of biological activities that support cellular activity and tissue regeneration in order to preserve tissue homeostasis. The outcomes support the use of MSCs and the exosomes they produce as a therapeutic option for a range of diseases. This review provides a brief overview of the source of MSC-EVs and outlines their physiological roles and biochemical capabilities. The elucidation of the role of MSC-EVs in the recovery and repair of hepatic tissues, as well as their contribution to maintaining tissue homeostasis, is discussed in relation to different chronic liver diseases. This review aims to provide new insights into the unique roles that MSC-EVs play in the treatment of chronic liver diseases.

Coexpression analysis of angiogenesis, proliferation, apoptosis, autophagy and SHH pathway genes involved in skin expansion

Skin and soft tissue expansion is a widely used technique in plastic surgery. However, the regulatory mechanisms associated with cellular processes involved in skin expansion are not well elucidated. In the present study, we aimed at exploring the transcriptome changes associated with skin expansion and profiling the difference in gene expression between the skin tissue in the top of the dilator and the skin tissue in the side of the dilator. A mouse model of skin expansion was established and RNA sequencing (RNA-Seq) was performed on samples collected at different time points. Differential expression analysis was performed using the DESeq2 package while STEM was used for time series clustering profiling. The regulatory networks were established and the functions of sets of genes were analyzed. The mRNA expression levels of candidate genes were validated by the quantitative RT-PCR. Among the skin tissue in the top of the dilator and normal samples at days 1, 3, 7, 14 and 28, 53 commonly upregulated and 7 commonly downregulated genes were identified while among the skin tissue in the side of the dilator and normal samples, 98 downregulated and 255 upregulated genes were identified. Genes differentially expressed among the skin tissue in the top of the dilator and normal samples were involved in coagulation and proliferation-associated pathways while those among the skin tissue in the side of the dilator and normal samples were involved in the inflammation, immune response, and defense response. Among the skin tissue in the top of the dilator and the skin tissue in the side of the dilator samples, 161 were constantly upregulated while 27 were constantly downregulated; these genes were enriched in the biological processes of cell adhesion and regulation of cell proliferation (n = 11). Furthermore, we identified that SHH signaling genes formed a coexpression regulatory network with cellular proliferation, apoptosis, autophagy and angiogenesis-related genes in the expanded skin. In conclusion, our findings can promote research and understanding of the mechanism of skin expansion and will find application in plastic surgery.

Occlusal Force Maintains Alveolar Bone Homeostasis via Type H Angiogenesis

Physiologically, teeth and periodontal tissues are exposed to occlusal forces throughout their lifetime. Following occlusal unloading, unbalanced bone remodeling manifests as a net alveolar bone (AB) loss. This phenomenon is termed alveolar bone disuse osteoporosis (ABDO), the underlying mechanism of which remains unclear. Type H vessels, a novel capillary subtype tightly coupled with osteogenesis, reportedly have a role in skeletal remodeling; however, their role in ABDO is not well studied. In the present study, we aimed to explore the pathogenesis of and therapies for ABDO. The study revealed that type H endothelium highly positive for CD31 and endomucin was identified in the periodontal ligament (PDL) but rarely in the AB of the mice. In hypofunctional PDL, the density of type H vasculature and coupled osterix+ (OSX+) osteoprogenitors declined significantly. In addition, the angiogenic factor Slit guidance ligand 3 (SLIT3) was downregulated in the disused PDL, and periodontal injection of the recombinant SLIT3 protein partially ameliorated type H vessel dysfunction and AB loss in ABDO mice. With regard to the molecular mechanism, a mechanosensory signaling circuit, PIEZO1/Ca2+/HIF-1α/SLIT3, was validated by applying cyclic compression to 3-dimensional-cultured PDL cells using the Flexcell FX-5000 compression system. In summary, PDL plays a pivotal role in mechanotransduction by translating physical forces into the intracellular signaling axis PIEZO1/Ca2+/HIF-1α/SLIT3, which promotes type H angiogenesis and OSX+ cell-related osteogenensis, thereby contributing to AB homeostasis. Our findings advance the understanding of PDL in AB disorders. Further therapies targeting SLIT3 may provide new insights into preventing bone loss in ABDO.

Type H vessels in osteogenesis, homeostasis, and related disorders

The vascular system plays a crucial role in bone tissue. Angiogenic and osteogenic processes are coupled through a spatial-temporal connection. Recent studies have identified three types of capillaries in the skeletal system. Compared with type L and E vessels, type H vessels express high levels of CD31 and endomucin, and function to couple angiogenesis and osteogenesis. Endothelial cells in type H vessels interact with osteolineage cells (e.g., osteoblasts, osteoclasts, and osteocytes) through cytokines or signaling pathways to maintain bone growth and homeostasis. In imbalanced bone homeostases, such as osteoporosis and osteoarthritis, it may be a new therapeutic strategy to regulate the endothelial cell activity in type H vessels to repair the imbalance. Here, we reviewed the latest progress in relevant factors or signaling pathways in coupling angiogenesis and osteogenesis. This review would contribute to further understanding the role and mechanisms of type H vessels in coupling angiogenic and osteogenic processes. Furthermore, it will facilitate the development of therapeutic approaches for bone disorders by targeting type H vessels.

Region-specific sympatho-adrenergic regulation of specialized vasculature in bone homeostasis and regeneration

Type H vessels couple angiogenesis with osteogenesis, while sympathetic cues regulate vascular and skeletal function. The crosstalk between sympathetic nerves and type H vessels in bone remains unclear. Here, we first identify close spatial connections between sympathetic nerves and type H vessels in bone, particularly in metaphysis. Sympathoexcitation, mimicked by isoproterenol (ISO) injection, reduces type H vessels and bone mass. Conversely, beta-2-adrenergic receptor (ADRB2) deficiency maintains type H vessels and bone mass in the physiological condition. In vitro experiments reveal indirect sympathetic modulation of angiogenesis via paracrine effects of mesenchymal stem cells (MSCs), which alter the transcription of multiple angiogenic genes in endothelial cells (ECs). Furthermore, Notch signaling in ECs underlies sympathoexcitation-regulated type H vessel formation, impacting osteogenesis and bone mass. Finally, propranolol (PRO) inhibits beta-adrenergic activity and protects type H vessels and bone mass against estrogen deficiency. These findings unravel the specialized neurovascular coupling in bone homeostasis and regeneration.

The Role of Gli1+ Mesenchymal Stem Cells in Osteogenesis of Craniofacial Bone

Glioma-associated oncogene homolog 1 (Gli1) is a transcriptional activator of hedgehog (Hh) signaling that regulates target gene expression and several cellular biological processes. Cell lineage tracing techniques have highlighted Gli1 as an ideal marker for mesenchymal stem cells (MSCs) in vivo. Gli1+ MSCs are critical for the osteogenesis of the craniofacial bone; however, the regulatory mechanism by which Gli1+ MSCs mediate the bone development and tissue regeneration of craniofacial bone has not been systematically outlined. This review comprehensively elucidates the specific roles of Gli1+ MSCs in craniofacial bone osteogenesis. In addition to governing craniofacial bone development, Gli1+ MSCs are associated with the tissue repair of craniofacial bone under pathological conditions. Gli1+ MSCs promote intramembranous and endochondral ossification of the craniofacial bones, and assist the osteogenesis of the craniofacial bone by improving angiopoiesis. This review summarizes the novel role of Gli1+ MSCs in bone development and tissue repair in craniofacial bones, which offers new insights into bone regeneration therapy.

Mesenchymal Stem Cell Aggregation-Released Extracellular Vesicles Induce CD31+ EMCN+ Vessels in Skin Regeneration and Improve Diabetic Wound Healing

The blood vessel system is essential for skin homeostasis and regeneration. While the heterogeneity of vascular endothelial cells has been emergingly revealed, whether a regeneration-relevant vessel subtype exists in skin remains unknown. Herein, a specialized vasculature in skin featured by simultaneous CD31 and EMCN expression contributing to the regeneration process is identified, the decline of which functionally underlies the impaired angiogenesis of diabetic nonhealing wounds. Moreover, enlightened by the developmental process that mesenchymal condensation induces angiogenesis, it is demonstrated that mesenchymal stem/stromal cell aggregates (CAs) provide an efficacious therapy to enhance regrowth of CD31+ EMCN+ vessels in diabetic wounds, which is surprisingly suppressed by pharmacological inhibition of extracellular vesicle (EV) release. It is further shown that CAs promote secretion of angiogenic protein-enriched EVs by proteomic analysis, which directly exert high efficacy in boosting CD31+ EMCN+ vessels and treating nonhealing diabetic wounds. These results add to the current knowledge on skin vasculature and help establish feasible strategies to benefit wound healing under diabetic condition.

Engineered exosomes reprogram Gli1+ cells in vivo to prevent calcification of vascular grafts and autologous pathological vessels

Calcification of autologous pathological vessels and tissue engineering blood vessels (TEBVs) is a thorny problem in clinic. However, there is no effective and noninvasive treatment that is available against the calcification of TEBVs and autologous pathological vessels. Gli1+ cells are progenitors of smooth muscle cells (SMCs) and can differentiate into osteoblast-like cells, leading to vascular calcification. Our results showed that the spatiotemporal distribution of Gli1+ cells in TEBVs was positively correlated with the degree of TEBV calcification. An anticalcification approach was designed consisting of exosomes derived from mesenchymal stem cells delivering lncRNA-ANCR to construct the engineered exosome-Ancr/E7-EXO. The results showed that Ancr/E7-EXO effectively targeted Gli1+ cells, promoting rapid SMC reconstruction and markedly inhibiting Gli1+ cell differentiation into osteoblast-like cells. Moreover, Ancr/E7-EXO significantly inhibited vascular calcification caused by chronic kidney disease. Therefore, Ancr/E7-EXO reprogrammed Gli1+ cells to prevent calcification of vascular graft and autologous pathological vessel, providing unique insights for an effective anticalcification.

Mesenchymal condensation in tooth development and regeneration: a focus on translational aspects of organogenesis

The teeth are vertebrate-specific, highly specialized organs performing fundamental functions of mastication and speech, the maintenance of which is crucial for orofacial homeostasis and is further linked to systemic health and human psychosocial well-being. However, with limited ability for self-repair, the teeth can often be impaired by traumatic, inflammatory, and progressive insults, leading to high prevalence of tooth loss and defects worldwide. Regenerative medicine holds the promise to achieve physiological restoration of lost or damaged organs, and in particular an evolving framework of developmental engineering has pioneered functional tooth regeneration by harnessing the odontogenic program. As a key event of tooth morphogenesis, mesenchymal condensation dictates dental tissue formation and patterning through cellular self-organization and signaling interaction with the epithelium, which provides a representative to decipher organogenetic mechanisms and can be leveraged for regenerative purposes. In this review, we summarize how mesenchymal condensation spatiotemporally assembles from dental stem cells (DSCs) and sequentially mediates tooth development. We highlight condensation-mimetic engineering efforts and mechanisms based on ex vivo aggregation of DSCs, which have achieved functionally robust and physiologically relevant tooth regeneration after implantation in animals and in humans. The discussion of this aspect will add to the knowledge of development-inspired tissue engineering strategies and will offer benefits to propel clinical organ regeneration.

The SHH-GLI1 pathway is required in skin expansion and angiogenesis

To investigate the role of GLI1 on skin proliferation and neovascularization during skin expansion in mice. We constructed GLI1-cre/R26-Tdtomato and GLI1-cre/R26-mtmg gene-tagged skin expansion mouse models. Using a two-photon in vivo imaging instrument to observe the changes in the number and distribution of GLI1(+) cells during the expansion process and to clarify the spatial relationship between GLI1(+) cells and blood vessels during the expansion process. In vitro proliferation assays were performed to further validate the effects of SHH (sonic hedgehog) and its downstream component GLI1 on cell proliferation viability. Finally, qRT-PCR was used to verify the changes in proliferation, angiogenesis-related factors, SHH signalling pathway-related factors, and the role of GLI1 cells in the process of skin expansion in mice. The number of GLI1(+) cells increased during dilation and were attached to the outer membrane of the vessel. The epidermis was thickened and the dermis thinned after the dilated skin was taken, while the epidermal thickening was suppressed and the dermis became thinner after the GLI1 cells were inhibited. The non-inhibited group showed a significant increase in PCNA positivity with prolonged dilation compared to the GANT61(GLI specificity inhibitor) inhibited group; CD31 immunofluorescence showed a significant increase in the number of dilated skin vessels and a significant decrease in the number of vessels after treatment with GANT61 inhibitor. In vitro proliferation results showed that SHH signalling activator significantly increased the proliferation viability of GLI1(+) hair follicle mesenchymal stem cells, while GNAT61 significantly inhibited the proliferation viability of GLI1(+) hair follicle mesenchymal stem cells. GLI1 is necessary for proliferation and neovascularization in expansion skin of mice through activation of the SHH signalling pathway.

Perinatal origins of bronchopulmonary dysplasia-deciphering normal and impaired lung development cell by cell

Bronchopulmonary dysplasia (BPD) is a multifactorial disease occurring as a consequence of premature birth, as well as antenatal and postnatal injury to the developing lung. BPD morbidity and severity depend on a complex interplay between prenatal and postnatal inflammation, mechanical ventilation, and oxygen therapy as well as associated prematurity-related complications. These initial hits result in ill-explored aberrant immune and reparative response, activation of pro-fibrotic and anti-angiogenic factors, which further perpetuate the injury. Histologically, the disease presents primarily by impaired lung development and an arrest in lung microvascular maturation. Consequently, BPD leads to respiratory complications beyond the neonatal period and may result in premature aging of the lung. While the numerous prenatal and postnatal stimuli contributing to BPD pathogenesis are relatively well known, the specific cell populations driving the injury, as well as underlying mechanisms are still not well understood. Recently, an effort to gain a more detailed insight into the cellular composition of the developing lung and its progenitor populations has unfold. Here, we provide an overview of the current knowledge regarding perinatal origin of BPD and discuss underlying mechanisms, as well as novel approaches to study the perturbed lung development.

Immunogenic Cell Death Associated Molecular Patterns and the Dual Role of IL17RA in Interstitial Cystitis/Bladder Pain Syndrome

The unclear etiology and pathogenesis of interstitial cystitis/bladder pain syndrome (IC/BPS) are responsible for the lack of effective treatment and the poor patient prognosis. Various studies show that chronic inflammation and immune responses are important factors contributing to the pathogenesis of IC/BPS. The process of immunogenic cell death (ICD) involves both the immune response and inflammatory process, and the involvement of ICD in IC/BPS pathogenesis has not been explored. Two IC/BPS transcriptome datasets collected from the Gene Expression Omnibus (GEO) database were used to identify distinct ICD-associated molecular patterns (IAMPs). IAMPs and IC/BPS subtypes were found to be related. The inflammatory immune microenvironments (IIME) in different IAMPs were studied. The potential mechanism by which the interleukin 17 receptor A (IL17RA) influences IC/BPS was examined using in vitro assays. The expression of ICD-related genes (IRGs) was upregulated in IC/BPS bladders, compared with normal bladders. Disease prediction models, based on differentially expressed IRGs, could accurately predict IC/BPS. The IC/BPS patients had two distinct IAMPs, each with its own subtype and clinical features and association with remodeling IIME. IL17RA, a well-established IC/BPS bladder biomarker, mediates both the inflammatory insult and the protective responses. In summary, the current study identified different IAMPs in IC/BPS, which may be involved in the pathogenesis of IC/BPS by remodeling the IIME. The chronic inflammatory process in IC/BPS may be prolonged by IL17RA, which could mediate both pro- and anti-inflammatory responses. The IL17RA-associated pathway may play a significant role in the development of IC/BPS and can be used as a therapeutic target.

Exosome-based bone-targeting drug delivery alleviates impaired osteoblastic bone formation and bone loss in inflammatory bowel diseases

Systematic bone loss is commonly complicated with inflammatory bowel diseases (IBDs) with unclear pathogenesis and uncertain treatment. In experimental colitis mouse models established by dextran sulfate sodium and IL-10 knockout induced with piroxicam, bone mass and quality are significantly decreased. Colitis mice demonstrate a lower bone formation rate and fewer osteoblasts in femur. Bone marrow mesenchymal stem/stromal cells (BMSCs) from colitis mice tend to differentiate into adipocytes rather than osteoblasts. Serum from patients with IBD promotes adipogenesis of human BMSCs. RNA sequencing reveals that colitis downregulates Wnt signaling in BMSCs. For treatment, exosomes with Golgi glycoprotein 1 inserted could carry Wnt agonist 1 and accumulate in bone via intravenous administration. They could alleviate bone loss, promote bone formation, and accelerate fracture healing in colitis mice. Collectively, BMSC commitment in inflammatory microenvironment contributes to lower bone quantity and quality and could be rescued by redirecting differentiation toward osteoblasts through bone-targeted drug delivery.

Correlation between stem cell molecular phenotype and atherosclerotic plaque neointima formation and analysis of stem cell signal pathways

Vascular stem cells exist in the three-layer structure of blood vessel walls and play an indispensable role in angiogenesis under physiological conditions and vascular remodeling under pathological conditions. Vascular stem cells are mostly quiescent, but can be activated in response to injury and participate in endothelial repair and neointima formation. Extensive studies have demonstrated the differentiation potential of stem/progenitor cells to repair endothelium and participate in neointima formation during vascular remodeling. The stem cell population has markers on the surface of the cells that can be used to identify this cell population. The main positive markers include Stem cell antigen-1 (Sca1), Sry-box transcription factor 10 (SOX10). Stromal cell antigen 1 (Stro-1) and Stem cell growth factor receptor kit (c-kit) are still controversial. Different parts of the vessel have different stem cell populations and multiple markers. In this review, we trace the role of vascular stem/progenitor cells in the progression of atherosclerosis and neointima formation, focusing on the expression of stem cell molecular markers that occur during neointima formation and vascular repair, as well as the molecular phenotypic changes that occur during differentiation of different stem cell types. To explore the correlation between stem cell molecular markers and atherosclerotic diseases and neointima formation, summarize the differential changes of molecular phenotype during the differentiation of stem cells into smooth muscle cells and endothelial cells, and further analyze the signaling pathways and molecular mechanisms of stem cells expressing different positive markers participating in intima formation and vascular repair. Summarizing the limitations of stem cells in the prevention and treatment of atherosclerotic diseases and the pressing issues that need to be addressed, we provide a feasible scheme for studying the signaling pathways of vascular stem cells involved in vascular diseases.

Aucubin Impeded Preosteoclast Fusion and Enhanced CD31hi EMCNhi Vessel Angiogenesis in Ovariectomized Mice

Osteogenesis is tightly correlated with angiogenesis during the process of bone development, regeneration, and remodeling. In addition to providing nutrients and oxygen for bone tissue, blood vessels around bone tissue also secrete some factors to regulate bone formation. Type H vessels which were regulated by platelet-derived growth factor-BB (PDGF-BB) were confirmed to couple angiogenesis and osteogenesis. Recently, preosteoclasts have been identified as the most important source of PDGF-BB. Therefore, inhibiting osteoclast maturation, improving PDGF-BB secretion, stimulating type H angiogenesis, and subsequently accelerating bone regeneration may be potent treatments for bone loss disease. In the present study, aucubin, an iridoid glycoside extracted from Aucuba japonica and Eucommia ulmoides, was found to inhibit bone loss in ovariectomized mice. We further confirmed that aucubin could inhibit the fusion of tartrate-resistant acid phosphatase (TRAP)+ preosteoclasts into mature osteoclasts and indirectly increasing angiogenesis of type H vessel. The underlying mechanism is the aucubin-induced inhibition of MAPK/NF-κB signaling, which increases the preosteoclast number and subsequently promotes angiogenesis via PDGF-BB. These results prompted that aucubin could be an antiosteoporosis drug candidate, which needs further research.

Optimized immunofluorescence staining protocol for identifying resident mesenchymal stem cells in bone using LacZ transgenic mice

Glioma-associated oncogene homolog 1 (Gli1) marks a subpopulation of endogenous mesenchymal stem cells (MSCs) characterized by perivascular location. Here, we present an optimized immunofluorescence staining protocol to identify resident Gli1⁺ MSCs in fixed/frozen bone sections from LacZ transgenic mice. This protocol describes the preparation of fixed/frozen tissue sections and the use of LacZ immunofluorescent staining for the in vivo characterization of endogenous MSCs, regarding their specific identity and specialized niches, and is applicable to LacZ-expressing cells of diverse organs. For complete details on the use and execution of this protocol, please refer to Chen et al. (2020).

Loss of Vlk in Prx1+ Cells Delays the Initial Steps of Endochondral Bone Formation and Fracture Repair in the Limb

Vertebrate lonesome kinase (Vlk) is a secreted tyrosine kinase important for normal skeletogenesis during embryonic development. Vlk null mice (Vlk^-/- ) are born with severe craniofacial and limb skeletal defects and die shortly after birth. We used a conditional deletion model to remove Vlk in limb bud mesenchyme (Vlk-Prx1 cKO) to assess the specific requirement for Vlk expression by skeletal progenitor cells during endochondral ossification, and an inducible global deletion model (Vlk-Ubq iKO) to address the role of Vlk during fracture repair. Deletion of Vlk with Prx1-Cre recapitulated the limb skeletal phenotype of the Vlk^-/- mice and enabled us to study the postnatal skeleton as Vlk-Prx1 cKO mice survived to adulthood. In Vlk-Prx1 cKO adult mice, limbs remained shorter with decreased trabecular and cortical bone volumes. Both Vlk-Prx1 cKO and Vlk-Ubq iKO mice had a delayed fracture repair response but eventually formed bridging calluses. Furthermore, levels of phosphorylated osteopontin (OPN) were decreased in tibias of Vlk-Ubq iKO, establishing OPN as a Vlk substrate in bone. In summary, our data indicate that Vlk produced by skeletal progenitor cells influences the timing and extent of chondrogenesis during endochondral bone formation and fracture repair. © 2022 American Society for Bone and Mineral Research (ASBMR).

Osteostatin improves the Osteogenic differentiation of mesenchymal stem cells and enhances angiogenesis through HIF-1α under hypoxia conditions in vitro

BACKGROUND

Hypoxia conditions induced by bone defects would prolong the duration of bone regeneration. The effect of osteostatin (OST) on the osteogenic differentiation of mesenchymal stem cells (MSCs) and angiogenesis under hypoxia conditions remain unexplored.

METHODS

SPF mice were obtained, and MSCs were isolated from bone marrow. MSCs were treated with 1% oxygen for hypoxia induction, and 200 nM of OST was used to treat cells under nomorxia or hypoxia conditions. Cell proliferation was evaluated using CCK8 assay, and trypan blue staining was implemented for determining cell death ratio. Alkaline phosphatase activity and alizarin redS staining was conducted to histologically evaluated osteogenic differentiation. Flow cytometry was used for the detection of CD31^hiEmcn^hi cells (Type H ECs), whose migration was detected by Transwell assay and angiogenesis was measured by tube formation assay. Protein level was measured by western blotting and mRNA level was monitored via RT-qPCR.

RESULTS

The MSC proliferation was enhanced by OST under hypoxia conditions. The osteogenic differentiation of MSCs was decreased under hypoxia conditions, and treatment of OST significantly reversed its inhibitory effect. The hypoxia treated culture medium of MSCs promoted the proliferation, migration, and angiogenesis of type H ECs, while the effects were further strengthened by OST addition. HIF-1α was found to be upregulated in hypoxia treated MSCs, whereas silencing of HIF-1α had reversed effects on the angiogenic capacity of Type H ECs.

CONCLUSION

OST improved the proliferation and osteogenic differentiation of MSCs and further promoted angiogenesis of type H ECs through upregulating HIF-1α expression.

Gli1 Regulates the Postnatal Acquisition of Peripheral Nerve Architecture

Peripheral nerves are organized into discrete compartments. Axons, Schwann cells (SCs), and endoneurial fibroblasts (EFs) reside within the endoneurium and are surrounded by the perineurium, a cellular sheath comprised of layers of perineurial glia (PNG). SC secretion of Desert Hedgehog (Dhh) regulates this organization. In Dhh nulls, the perineurium is deficient and the endoneurium is subdivided into small compartments termed minifascicles. Human Dhh mutations cause a neuropathy with similar defects. Here we examine the role of Gli1, a canonical transcriptional effector of hedgehog signaling, in regulating peripheral nerve organization in mice of both genders. We identify PNG, EFs, and pericytes as Gli1-expressing cells by genetic fate mapping. Although expression of Dhh by SCs and Gli1 in target cells is coordinately regulated with myelination, Gli1 expression unexpectedly persists in Dhh null EFs. Thus, Gli1 is expressed in EFs noncanonically (i.e., independent of hedgehog signaling). Gli1 and Dhh also have nonredundant activities. Unlike Dhh nulls, Gli1 nulls have a normal perineurium. Like Dhh nulls, Gli1 nulls form minifascicles, which we show likely arise from EFs. Thus, Dhh and Gli1 are independent signals: Gli1 is dispensable for perineurial development but functions cooperatively with Dhh to drive normal endoneurial development. During development, Gli1 also regulates endoneurial extracellular matrix production, nerve vascular organization, and has modest, nonautonomous effects on SC sorting and myelination of axons. Finally, in adult nerves, induced deletion of Gli1 is sufficient to drive minifascicle formation. Thus, Gli1 regulates the development and is required to maintain the endoneurial architecture of peripheral nerves.SIGNIFICANCE STATEMENT Peripheral nerves are organized into distinct cellular/ECM compartments: the epineurium, perineurium, and endoneurium. This organization, with its associated cellular constituents, is critical for the structural and metabolic support of nerves and their response to injury. Here, we show that Gli1, a transcription factor normally expressed downstream of hedgehog signaling, is required for the proper organization of the endoneurium but not the perineurium. Unexpectedly, Gli1 expression by endoneurial cells is independent of, and functions nonredundantly with, Schwann Cell-derived Desert Hedgehog in regulating peripheral nerve architecture. These results further delineate how peripheral nerves acquire their distinctive organization during normal development, and highlight mechanisms that may regulate their reorganization in pathologic settings, including peripheral neuropathies and nerve injury.

Gli1+ Mesenchymal Stem Cells in Bone and Teeth

Mesenchymal stem cells (MSCs) are remarkable and noteworthy. Identification of markers for MSCs enables the study of their niche in vivo. It has been identified that glioma-associated oncogene 1 positive (Gli1+) cells are mesenchymal stem cells supporting homeostasis and injury repair, especially in the skeletal system and teeth. This review outlines the role of Gli1+ cells as an MSC subpopulation in both bones and teeth, suggesting the prospects of Gli1+ cells in stem cell-based tissue engineering.

Mechanically-regulated bone repair

Fracture healing is a complex, multistep process that is highly sensitive to mechanical signaling. To optimize repair, surgeons prescribe immediate weight-bearing as-tolerated within 24 hours after surgical fixation; however, this recommendation is based on anecdotal evidence and assessment of bulk healing outcomes (e.g., callus size, bone volume, etc.). Given challenges in accurately characterizing the mechanical environment and the ever-changing properties of the regenerate, the principles governing mechanical regulation of repair, including their cell and molecular basis, are not yet well defined. However, the use of mechanobiological rodent models, and their relatively large genetic toolbox, combined with recent advances in imaging approaches and single-cell analyses is improving our understanding of the bone microenvironment in response to loading. This review describes the identification and characterization of distinct cell populations involved in bone healing and highlights the most recent findings on mechanical regulation of bone homeostasis and repair with an emphasis on osteo-angio coupling. A discussion on aging and its impact on bone mechanoresponsiveness emphasizes the need for novel mechanotherapeutics that can re-sensitize skeletal stem and progenitor cells to physical rehabilitation protocols.

Improved osseointegration of strontium-modified titanium implant by regulating angiogenesis and macrophage polarization

Strotium (Sr) has shown strong osteogenic potential and thereby been widely incorporated into dental and orthopedic implants. However, the improved osseointegration of strontium-modified titanium implant through regulation of angiogenesis and macrophage...

Research progress on the hedgehog signalling pathway in regulating bone formation and homeostasis

Bone formation is a complex regeneration process that was regulated by many signalling pathways, such as Wnt, Notch, BMP and Hedgehog (Hh). All of these signalling have been demonstrated to participate in the bone repair process. In particular, one promising signalling pathway involved in bone formation and homeostasis is the Hh pathway. According to present knowledge, Hh signalling plays a vital role in the development of various tissues and organs in the embryo. In adults, the dysregulation of Hh signalling has been verified to be involved in bone‐related diseases in terms of osteoarthritis, osteoporosis and bone fracture; and during the repair processes, Hh signalling could be reactivated and further modulate bone formation. In this chapter, we summarize our current understanding on the function of Hh signalling in bone formation and homeostasis. Additionally, the current therapeutic strategies targeting this cascade to coordinate and mediate the osteogenesis process have been reviewed.

Mechanical loading alleviated the inhibition of β2-adrenergic receptor agonist terbutaline on bone regeneration

The long-term use of adrenergic medication in treating various conditions, such as asthma, increases the chances of bone fracture. Dynamic mechanical loading at a specific time is a method for improving bone quality and promoting healing. Therefore, we hypothesized that precisely controlling the mechanical environment can contribute to the alleviation of the negative effects of chronic treatment with the common asthma drug terbutaline, which is a β2-adrenergic receptor agonist that facilitates bone homeostasis and defect repair through its anabolic effect on osteogenic cells. Our in vitro results showed that terbutaline can directly inhibit osteogenesis by impairing osteogenic differentiation and mineralization. Chronic treatment in vivo was simulated by administering terbutaline to C57BL/6J mice for 4 weeks before bone defect surgery and mechanical loading. We utilized a stabilized tibial defect model, which allowed the application of anabolic mechanical loading. During homeostasis, chronic terbutaline treatment reduced the bone formation rate, the fracture toughness of long bones, and the concentrations of bone formation markers in the sera. During defect repair, terbutaline decreased the bone volume, type H vessel, and total blood vessel volume. Terbutaline treatment reduced the number of osteogenic cells. Periostin, which was secreted mainly by Prrx1+ osteoprogenitors and F4/80+ macrophages, was inhibited by treating the bone defect with terbutaline. Interestingly, controlled mechanical loading facilitated the recovery of bone volume and periostin expression and the number of osteogenic cells within the defect. In conclusion, mechanical loading can rescue negative effects on new bone accrual and repair induced by chronic terbutaline treatment.

The endothelium-bone axis in development, homeostasis and bone and joint disease

Blood vessels form a versatile transport network that is best known for its critical roles in processes such as tissue oxygenation, metabolism and immune surveillance. The vasculature also provides local, often organ-specific, molecular signals that control the behaviour of other cell types in their vicinity during development, homeostasis and regeneration, and also in disease processes. In the skeletal system, the local vasculature is actively involved in both bone formation and resorption. In addition, blood vessels participate in inflammatory processes and contribute to the pathogenesis of diseases that affect the joints, such as rheumatoid arthritis and osteoarthritis. This Review summarizes the current understanding of the architecture, angiogenic growth and functional properties of the bone vasculature. The effects of ageing and pathological conditions, including arthritis and osteoporosis, are also discussed.

Gli1+ Cells Residing in Bone Sutures Respond to Mechanical Force via IP3R to Mediate Osteogenesis

Early orthodontic correction of skeletal malocclusion takes advantage of mechanical force to stimulate unclosed suture remodeling and to promote bone reconstruction; however, the underlying mechanisms remain largely unclear. Gli1⁺ cells in maxillofacial sutures have been shown to participate in maxillofacial bone development and damage repair. Nevertheless, it remains to be investigated whether these cells participate in mechanical force-induced bone remodeling during orthodontic treatment of skeletal malocclusion. In this study, rapid maxillary expansion (RME) mouse models and mechanical stretch loading cell models were established using two types of transgenic mice which are able to label Gli1⁺ cells, and we found that Gli1⁺ cells participated in mechanical force-induced osteogenesis both in vivo and in vitro. Besides, we found mechanical force-induced osteogenesis through inositol 1,4,5-trisphosphate receptor (IP₃R), and we observed for the first time that inhibition of Gli1 suppressed an increase in mechanical force-induced IP3R overexpression, suggesting that Gli1⁺ cells participate in mechanical force-induced osteogenesis through IP₃R. Taken together, this study is the first to demonstrate that Gli1⁺ cells in maxillofacial sutures are involved in mechanical force-induced bone formation through IP₃R during orthodontic treatment of skeletal malocclusion. Furthermore, our results provide novel insights regarding the mechanism of orthodontic treatments of skeletal malocclusion.

Apoptotic vesicles restore liver macrophage homeostasis to counteract type 2 diabetes

Apoptosis is a naturally occurring process generating plenty of apoptotic vesicles (apoVs), but the feature, fate and function of apoVs remain largely unknown. Notably, as an appealing source for cell therapy, mesenchymal stem cells (MSCs) undergo necessary apoptosis and release apoVs during therapeutic application. In this study, we characterized and used MSC‐derived apoVs to treat type 2 diabetes (T2D) mice, and we found that apoVs were efferocytosed by macrophages and functionally modulated liver macrophage homeostasis to counteract T2D. We showed that apoVs can induce macrophage reprogramming at the transcription level in an efferocytosis‐dependent manner, leading to inhibition of macrophage accumulation and transformation of macrophages towards an anti‐inflammation phenotype in T2D liver. At the molecular level, we discovered that calreticulin (CRT) was exposed on the surface of apoVs to act as a critical ‘eat‐me’ signal mediating apoV efferocytosis and macrophage regulatory effects. Importantly, we demonstrated that CRT‐mediated efferocytosis of MSC‐derived apoVs contributes to T2D therapy with alleviation of T2D phenotypes including glucose intolerance and insulin resistance. These findings uncover that functional efferocytosis of apoVs restores liver macrophage homeostasis and ameliorates T2D.

The vital role of Gli1+ mesenchymal stem cells in tissue development and homeostasis

The hedgehog (Hh) signaling pathway plays an essential role in both tissue development and homeostasis. Glioma-associated oncogene homolog 1 (Gli1) is one of the vital transcriptional factors as well as the direct target gene in the Hh signaling pathway. The cells expressing the Gli1 gene (Gli1⁺ cells) have been identified as mesenchymal stem cells (MSCs) that are responsible for various tissue developments, homeostasis, and injury repair. This review outlines some recent discoveries on the crucial roles of Gli1⁺ MSCs in the development and homeostasis of varieties of hard and soft tissues.

Molecular and cellular mechanisms of aging in hematopoietic stem cells and their niches

Aging drives the genetic and epigenetic changes that result in a decline in hematopoietic stem cell (HSC) functioning. Such changes lead to aging-related hematopoietic/immune impairments and hematopoietic disorders. Understanding how such changes are initiated and how they progress will help in the development of medications that could improve the quality life for the elderly and to treat and possibly prevent aging-related hematopoietic diseases. Here, we review the most recent advances in research into HSC aging and discuss the role of HSC-intrinsic events, as well as those that relate to the aging bone marrow niche microenvironment in the overall processes of HSC aging. In addition, we discuss the potential mechanisms by which HSC aging is regulated.