Integrating network pharmacology and experimental validation reveals therapeutic effects of D-mannose on NAFLD through mTOR suppression

Non-alcoholic fatty liver disease (NAFLD), a chronic liver condition and metabolic disorder, has emerged as a significant health issue worldwide. D-mannose, a natural monosaccharide widely existing in plants and animals, has demonstrated metabolic regulatory properties. However, the effect and mechanism by which D-mannose may counteract NAFLD have not been studied. In this study, network pharmacology followed by molecular docking analysis was utilized to identify potential targets of mannose against NAFLD, and the leptin receptor-deficient, genetically obese db/db mice was employed as an animal model of NAFLD to validate the regulation of D-mannose on core targets. As a result, 67 targets of mannose are predicted associated with NAFLD, which are surprisingly centered on the mechanistic target of rapamycin (mTOR). Further analyses suggest that mTOR signaling is functionally enriched in potential targets of mannose treating NAFLD, and that mannose putatively binds to mTOR as a core mechanism. Expectedly, repeated oral gavage of supraphysiological D-mannose ameliorates liver steatosis of db/db mice, which is based on suppression of hepatic mTOR signaling. Moreover, daily D-mannose administration reduced hepatic expression of lipogenic regulatory genes in counteracting NAFLD. Together, these findings reveal D-mannose as an effective and potential NAFLD therapeutic through mTOR suppression, which holds translational promise.

[Theory and practice of mesenchymal condensation directing tooth development and regeneration]

Mesenchymal stem cells, under spatiotemporal regulation of genes and microenvironment, are capable of spontaneously aggregating into dense regions, a phenomenon known as mesenchymal condensation. Mesenchymal condensation is an evolutionarily conserved developmental event that is critical in initiating morphogenesis of teeth and systemic organs. Mesenchymal stem cells hold the intrinsic ability to self-assemble in culture, and the generation of stem cell aggregates based on this property that mimics developmental mesenchymal condensation has become a potent and promising approach in regenerative medicine. This review discusses the mesenchymal condensation principles and its role as well as mechanism in tooth morphogenesis, as well as the engineering strategies for constructing mesenchymal stem cell aggregates and their application experience in tooth regeneration. It aims to start from the perspective of "development-inspired regeneration" and provide insights into understanding stem cell developmental biology and establishing new organ regenerative strategies.

[Study on liver tissue derived-extracellular vesicles regulating the osteogenic differentiation ability of mesenchymal stem cells and promoting the healing of jaw bone defects]

Objective: To explore the biological process of liver tissue-derived extracellular vesicle (LT-EV) in promoting osteogenic differentiation of mesenchymal stem cells and healing of jaw defects to provide a feasible treatment method for the clinical treatment of jaw bone defects. Methods: Enzymatic hydrolysis and differential centrifugation were used to extract LT-EV, scanning electron microscopy, Western blotting, and nanoparticle tracking analyzers were used to identify and characterize LT-EV, and further to explore the biological functions of LT-EV through proteomics and Kyoto Encyclopedia of Genes and Genomes. Flow cytometry was used to detect LT-EV plasma concentration and to calculate the plasma half-life of LT-EV. Small animal in vivo imaging system was used to detect the biological distribution of LT-EV 24 hours after injection. Six C57BL/6 mice were divided into control group and LT-EV group (3 mice in each group) by simple random sampling method. All mice underwent jaw bone defect surgery and tail vein injection every 7 days (the control group was injected with phosphoric buffer saline, LT-EV group was injected with LT-EV), micro-CT was used to evaluate the degree of mouse jaw bone healing 28 days after surgery, HE staining was used to analyze the multi-organ biosafety of LT-EV, and immunofluorescence staining was used to detect the jaw bone expression of osteogenic marker proteins in the defect area. Human jaw bone mesenchymal stem cells (hJBMSC) induced by osteogenic differentiation were treated with LT-EV (obtained from orthognathic surgery patients provided by the Department of Traumatology and Orthognathic Surgery of School of Stomatology of The Fourth Military Medical University resected normal jaw bone fragments), and the difference in osteogenic differentiation ability between the hJBMSC group and the control group (phosphate buffer saline treatment) was compared, and the in vitro bone differentiation promoting effect of LT-EV was verified through alkaline phosphatase (ALP) staining and real-time fluorescence quantitative PCR. Results: The yield of LT-EV was high, and proteomics and Kyoto Encyclopedia of Genes and Genomes showed that LT-EV contained a series of proteins that regulated cell biological functions. LT-EV injected into the tail vein could reach the mouse jaw bone defect area and promote the regeneration and repair of the jaw bone defect [the bone volume fractions of the LT-EV group and the control group were (36.06±4.20)% and (18.58±5.61)%, respectively; t=4.32, P=0.013], and had good biosafety. LT-EV could promote osteogenic differentiation of hJBMSC in vitro. Compared to the control group, ALP staining and osteogenic gene expression levels were significantly enhanced after osteogenic differentiation of hJBMSC (P<0.05). Conclusions: LT-EV exhibits a high yield, ease of acquisition, high biological safety, and excellent bone-promoting effects. It holds promise as a novel cell-free therapy strategy for regenerating craniofacial bone defects.

[Analysis of the differences in the characteristics of mesenchymal stem cells derived from jaw and long bones based on single-cell RNA-sequencing]

Objective: To study the whole bone marrow cellular composition of jaw and long bones, and further analyze the heterogeneity of mesenchymal stem cells (MSCs) derived from these two tissue, aiming at exploring the differences in functional characteristics of bone MSCs from different lineage sources. Methods: The Seurat package of R language was used to analyze the mandibular and femur whole bone marrow single-cell RNA-sequencing (scRNA-seq) datasets in the literature, and the subpopulations were annotated by reference to the marker genes reported by previous studies. The differentially expressed genes between mandible-derived MSCs (M-MSCs) and femur-derived MSCs (F-MSCs) were calculated, and cell-cell communication analysis between M-MSCs or F-MSCs with other cell populations was performed. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed on up-regulated and down-regulated differentially expressed genes of M-MSCs, and Gene Set Enrichment Analysis (GSEA) was performed on M-MSCs or F-MSCs. Results: cRNA-seq analysis showed that the mandible and femur had the same bone marrow cell composition, but there were differences in the proportion of specific cell populations. Also, there were significantly differentially expressed genes between M-MSCs and F-MSCs. In addition, cell-cell communication analysis revealed differences in numbers of ligand-receptor pairs between M-MSCs or F-MSCs with other cell populations. Furthermore, GO, KEGG and GSEA analysis showed that M-MSCs had higher extracellular matrix production potential than F-MSCs, but had lower ability to regulate other cells in the bone marrow, especially immune cells. Conclusions: M-MSCs and F-MSCs showed distinct differences in the gene expression pattern and up-regulated signaling pathways, which may be closely related to the developmental sources and functional characteristics of jaw and long bones.

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.

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.

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.

Proteomic analysis identifies Stomatin as a biological marker for psychological stress

Psychological stress emerges to be a common health burden in the current society for its highly related risk of mental and physical disease outcomes. However, how the quickly-adaptive stress response process connects to the long-observed organismal alterations still remains unclear. Here, we investigated the profile of circulatory extracellular vesicles (EVs) after acute stress (AS) of restraint mice by phenotypic and proteomic analyses. We surprisingly discovered that AS-EVs demonstrated significant changes in size distribution and plasma concentration compared to control group (CN) EVs. AS-EVs were further characterized by various differentially expressed proteins (DEPs) closely associated with biological, metabolic and immune regulations and were functionally important in potentially underlying multiple diseases. Notably, we first identified the lipid raft protein Stomatin as an essential biomarker expressed on the surface of AS-EVs. These findings collectively reveal that EVs are a significant function-related liquid biopsy indicator that mediate circulation alterations impinged by psychological stress, while also supporting the idea that psychological stress-associated EV-stomatin can be used as a biomarker for potentially predicting acute stress responses and monitoring psychological status. Our study will pave an avenue for implementing routine plasma EV-based theranostics in the clinic.

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).

Mesenchymal stem cell-derived exosomes: A novel and potential remedy for cutaneous wound healing and regeneration

Poor healing of cutaneous wounds is a common medical problem in the field of traumatology. Due to the intricate pathophysiological processes of wound healing, the use of conventional treatment methods, such as chemical molecule drugs and traditional dressings, have been unable to achieve satisfactory outcomes. Within recent years, explicit evidence suggests that mesenchymal stem cells (MSCs) have great therapeutic potentials on skin wound healing and regeneration. However, the direct application of MSCs still faces many challenges and difficulties. Intriguingly, exosomes as cell-secreted granular vesicles with a lipid bilayer membrane structure and containing specific components from the source cells may emerge to be excellent substitutes for MSCs. Exosomes derived from MSCs (MSC-exosomes) have been demonstrated to be beneficial for cutaneous wound healing and accelerate the process through a variety of mechanisms. These mechanisms include alleviating inflammation, promoting vascularization, and promoting proliferation and migration of epithelial cells and fibroblasts. Therefore, the application of MSC-exosomes may be a promising alternative to cell therapy in the treatment of cutaneous wounds and could promote wound healing through multiple mechanisms simultaneously. This review will provide an overview of the role and the mechanisms of MSC-derived exosomes in cutaneous wound healing, and elaborate the potentials and future perspectives of MSC-exosomes application in clinical practice.

Sympathetic Neurostress Drives Osteoblastic Exosomal MiR-21 Transfer to Disrupt Bone Homeostasis and Promote Osteopenia

Innervation and extracellular vesicle secretion co-exist in the local tissue microenvironment for message transfer, but whether they are interconnected to regulate organ homeostasis remains unknown. Sympatho-adrenergic activation is implicated in stress-induced depression and leads to bone loss, but the mechanisms and therapeutics are incompletely elucidated. Here, it is revealed that sympathetic neurostress through the β_1/2 -adrenergic receptor (β1/2-AR) signaling triggers the transcription response of a microRNA, miR-21, in osteoblasts, which is transferred to osteoclast progenitors via exosomes for dictating osteoclastogenesis. After confirming that miR-21 deficiency retards the β1/2-AR agonist isoproterenol (ISO)-induced osteopenia, it is shown that the pharmacological inhibition of exosome release by two clinically-relevant drugs, dimethyl amiloride and omeprazole, suppresses osteoblastic miR-21 transfer and ameliorates bone loss under both ISO and chronic variable stress (CVS)-induced depression conditions. A targeted delivery approach to specifically silence osteoblastic miR-21 is further applied, which is effective in rescuing the bone remodeling balance and ameliorating ISO- and CVS-induced osteopenias. These results decipher a previously unrecognized paradigm that neural cues drive exosomal microRNA communication to regulate organ homeostasis and help to establish feasible strategies to counteract bone loss under psychological stresses.

Glycemic control by umbilical cord-derived mesenchymal stem cells promotes effects of fasting-mimicking diet on type 2 diabetic mice

BACKGROUND

Hepatic steatosis is a big hurdle to treat type 2 diabetes (T2D). Fasting-mimicking diet (FMD) has been shown to be an effective intervention in dyslipidemia of T2D. However, fasting may impair the normal glucose metabolism. Human umbilical cord-derived mesenchymal stem cell (UC-MSC) transplantation has been discovered to regulate immune reactions and reduce hyperglycemia in diabetes. However, the effect of UC-MSCs on improving the lipid metabolism disorder is not quite satisfactory. We have investigated the efficacy comparison and interaction between FMD and UC-MSC infusion, aiming to establish effective T2D therapies and explore its mechanism.

METHODS

C57/BL6 mice were fed with high-fat diet (HFD) to induce a diet-induced obese (DIO) mouse model. Leptin receptor-deficient (db/db) mice were used for follow-up experiments. DIO or db/db mice were divided into 4 groups: phosphate buffer saline (PBS), UC-MSCs, FMD, and UC-MSCs + FMD. At the end of the study period, mice were fasted and sacrificed, with the measurement of physiological and biochemical indexes. In addition, the fresh liver, skin, and white adipose tissue were analyzed by histology.

RESULTS

FMD restored the lipid metabolism in DIO mice, whereas its capacity to rescue hyperglycemia was uncertain. Infusion of UC-MSCs was effective in T2D glycemic control but the impact on dyslipidemia was insufficient. Furthermore, both the glucose and the lipid alterations of DIO and db/db mice recovered after UC-MSCs combined with FMD. It was proved that UC-MSCs promoted FMD effects on ameliorating hyperglycemia and restoring the lipid metabolism in T2D mice, while FMD had little promotion effect on UC-MSCs. Mechanistically, we discovered that UC-MSC infusion significantly modulated systematic inflammatory microenvironment, which contributed to concerted actions with FMD.

CONCLUSIONS

We established a strategy that combined UC-MSC infusion and FMD and was effective in treating T2D, which provided potential approaches for developing novel clinical T2D therapies.

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

Mesenchymal stem/stromal cells (MSCs) reside in the perivascular niche and modulate tissue/organ homeostasis; however, little is known about whether and how their localization and function are linked. Particularly, whether specific MSC subsets couple with and regulate specialized vessel subtypes is unclear. Here, we show that Gli1⁺ cells, which are a subpopulation of MSCs couple with and regulate a specialized form of vasculature. The specific capillaries, i.e., CD31^hiEMCN^hi type H vessels, are the preferable vascular subtype which Gli1⁺ cells are adjacent to in bone. Gli1⁺ cells are further identified to be phenotypically coupled with type H endothelium during bone growth and defect healing. Importantly, Gli1⁺ cell ablation inhibits type H vessel formation associated with suppressed bone generation and regeneration. Mechanistically, Gli1⁺ cells initiate angiogenesis through Gli and HIF-1α signaling. These findings suggest a morphological and functional framework of Gli1⁺ cells modulating coupled type H vasculature for tissue homeostasis and regenerative repair.

Mechanosensing by Gli1+ cells contributes to the orthodontic force-induced bone remodelling

Objectives

Gli1⁺ cells have received extensive attention in tissue homeostasis and injury mobilization. The aim of this study was to investigate whether Gli1⁺ cells respond to force and contribute to bone remodelling.

Materials and methods

We established orthodontic tooth movement (OTM) model to assess the bone response for mechanical force. The transgenic mice were utilized to label and inhibit Gli1⁺ cells, respectively. Additionally, mice that conditional ablate Yes‐associated protein (Yap) in Gli1⁺ cells were applied in the present study. The tooth movement and bone remodelling were analysed.

Results

We first found Gli1⁺ cells expressed in periodontal ligament (PDL). They were proliferated and differentiated into osteoblastic cells under tensile force. Next, both pharmacological and genetic Gli1 inhibition models were utilized to confirm that inhibition of Gli1⁺ cells led to arrest of bone remodelling. Furthermore, immunofluorescence staining identified classical mechanotransduction factor Yap expressed in Gli1⁺ cells and decreased after suppression of Gli1⁺ cells. Additionally, conditional ablation of Yap gene in Gli1⁺ cells inhibited the bone remodelling as well, suggesting Gli1⁺ cells are force‐responsive cells.

Conclusions

Our findings highlighted that Gli1⁺ cells in PDL directly respond to orthodontic force and further mediate bone remodelling, thus providing novel functional evidence in the mechanism of bone remodelling and first uncovering the mechanical responsive property of Gli1⁺ cells.

Mitochondrial Regulation of Stem Cells in Bone Homeostasis

Mitochondria have emerged as key contributors to the organismal homeostasis, in which mitochondrial regulation of stem cells is becoming increasingly important. Originated from mesenchymal stem cell (MSC) and hematopoietic stem cell (HSC) lineage commitments and interactions, bone is a representative organ where the mitochondrial essentiality to stem cell function has most recently been discovered, underlying skeletal health, aging, and diseases. Furthermore, mitochondrial medications based on modulating stem cell specification are emerging to provide promising therapies to counteract bone aging and pathologies. Here we review the cutting-edge knowledge regarding mitochondrial regulation of stem cells in bone homeostasis, highlighting mechanistic insights as well as mitochondrial strategies for augmented bone healing and tissue regeneration.

NDRG2 suppression as a molecular hallmark of photoreceptor-specific cell death in the mouse retina

Photoreceptor cell death is recognized as the key pathogenesis of retinal degeneration, but the molecular basis underlying photoreceptor-specific cell loss in retinal damaging conditions is virtually unknown. The N-myc downstream regulated gene (NDRG) family has recently been reported to regulate cell viability, in particular NDRG1 has been uncovered expression in photoreceptor cells. Accordingly, we herein examined the potential roles of NDRGs in mediating photoreceptor-specific cell loss in retinal damages. By using mouse models of retinal degeneration and the 661 W photoreceptor cell line, we showed that photoreceptor cells are indeed highly sensitive to light exposure and the related oxidative stress, and that photoreceptor cells are even selectively diminished by phototoxins of the alkylating agent N-Methyl-N-nitrosourea (MNU). Unexpectedly, we discovered that of all the NDRG family members, NDRG2, but not the originally hypothesized NDRG1 or other NDRG subtypes, was selectively expressed and specifically responded to retinal damaging conditions in photoreceptor cells. Furthermore, functional experiments proved that NDRG2 was essential for photoreceptor cell viability, which could be attributed to NDRG2 control of the photo-oxidative stress, and that it was the suppression of NDRG2 which led to photoreceptor cell loss in damaging conditions. More importantly, NDRG2 preservation contributed to photoreceptor-specific cell maintenance and retinal protection both in vitro and in vivo. Our findings revealed a previously unrecognized role of NDRG2 in mediating photoreceptor cell homeostasis and established for the first time the molecular hallmark of photoreceptor-specific cell death as NDRG2 suppression, shedding light on improved understanding and therapy of retinal degeneration.

Resveratrol enhances the functionality and improves the regeneration of mesenchymal stem cell aggregates

Mesenchymal stem cell (MSC)-based regeneration, specifically cell aggregate or cell sheet engineering, is a promising approach for tissue reconstruction. Considering the advantages of ease of harvest and lack of immune rejection, the application of autologous MSCs (i.e., patients' own MSCs) in regenerative medicine has developed considerable interest. However, the impaired cell viability and regenerative potential following MSCs impacted by disease remain a major challenge. Resveratrol (RSV) exhibits reliable and extensive rejuvenative activities that have received increasing clinical attention. Here, we uncovered that resveratrol enhances the functionality and improves the regeneration of mesenchymal stem cell aggregates. Periodontal ligament MSCs (PDLSCs) from normal control subjects (N-PDLSCs) and periodontitis patients (P-PDLSCs) were investigated. Compared to N-PDLSCs, P-PDLSCs were less capable of forming cell aggregates, and P-PDLSC aggregates showed impaired osteogenesis and regeneration. These functional declines could be mimicked in N-PDLSCs by tumor necrosis factor alpha (TNF-α) treatment. Notably, a TNF-α-induced functional decline in N-PDLSC aggregates was rescued by RSV application. More importantly, in both N-PDLSCs and P-PDLSCs, RSV promoted cell aggregate formation and improved their osteogenic potential. Furthermore, as proven ectopically in vivo, the tissue regenerative capability of P-PDLSC aggregates was also enhanced after RSV treatment during aggregate formation in vitro. Finally, in a rat in situ regeneration model, we successfully applied both N-PDLSC aggregates and P-PDLSC aggregates to repair periodontal defects upon long-term functional improvements by RSV preconditioning. Together, our data unravel a novel methodology for using pharmacology (i.e., RSV)-based cell aggregate engineering to improve the functionality and facilitate the regeneration of MSCs from both healthy and inflammatory microenvironments, shedding light on improving the application of autologous MSC-mediated regenerative medicine.

Reconstruction of structure and function in tissue engineering of solid organs: Toward simulation of natural development based on decellularization

Failure of solid organs, such as the heart, liver, and kidney, remains a major cause of the world's mortality due to critical shortage of donor organs. Tissue engineering, which uses elements including cells, scaffolds, and growth factors to fabricate functional organs in vitro, is a promising strategy to mitigate the scarcity of transplantable organs. Within recent years, different construction strategies that guide the combination of tissue engineering elements have been applied in solid organ tissue engineering and have achieved much progress. Most attractively, construction strategy based on whole-organ decellularization has become a popular and promising approach, because the overall structure of extracellular matrix can be well preserved. However, despite the preservation of whole structure, the current constructs derived from decellularization-based strategy still perform partial functions of solid organs, due to several challenges, including preservation of functional extracellular matrix structure, implementation of functional recellularization, formation of functional vascular network, and realization of long-term functional integration. This review overviews the status quo of solid organ tissue engineering, including both advances and challenges. We have also put forward a few techniques with potential to solve the challenges, mainly focusing on decellularization-based construction strategy. We propose that the primary concept for constructing tissue-engineered solid organs is fabricating functional organs based on intact structure via simulating the natural development and regeneration processes.

Resveratrol counteracts bone loss via mitofilin-mediated osteogenic improvement of mesenchymal stem cells in senescence-accelerated mice

Rational: Senescence of mesenchymal stem cells (MSCs) and the related functional decline of osteogenesis have emerged as the critical pathogenesis of osteoporosis in aging. Resveratrol (RESV), a small molecular compound that safely mimics the effects of dietary restriction, has been well documented to extend lifespan in lower organisms and improve health in aging rodents. However, whether RESV promotes function of senescent stem cells in alleviating age-related phenotypes remains largely unknown. Here, we intend to investigate whether RESV counteracts senescence-associated bone loss via osteogenic improvement of MSCs and the underlying mechanism.

Methods: MSCs derived from bone marrow (BMMSCs) and the bone-specific, senescence-accelerated, osteoblastogenesis/osteogenesis-defective mice (the SAMP6 strain) were used as experimental models. In vivo application of RESV was performed at 100 mg/kg intraperitoneally once every other day for 2 months, and in vitro application of RESV was performed at 10 μM. Bone mass, bone formation rates and osteogenic differentiation of BMMSCs were primarily evaluated. Metabolic statuses of BMMSCs and the mitochondrial activity, transcription and morphology were also examined. Mitofilin expression was assessed at both mRNA and protein levels, and short hairpin RNA (shRNA)-based gene knockdown was applied for mechanistic experiments.

Results: Chronic intermittent application of RESV enhances bone formation and counteracts accelerated bone loss, with RESV improving osteogenic differentiation of senescent BMMSCs. Furthermore, in rescuing osteogenic decline under BMMSC senescence, RESV restores cellular metabolism through mitochondrial functional recovery via facilitating mitochondrial autonomous gene transcription. Molecularly, in alleviating senescence-associated mitochondrial disorders of BMMSCs, particularly the mitochondrial morphological alterations, RESV upregulates Mitofilin, also known as inner membrane protein of mitochondria (Immt) or Mic60, which is the core component of the mitochondrial contact site and cristae organizing system (MICOS). Moreover, Mitofilin is revealed to be indispensable for mitochondrial homeostasis and osteogenesis of BMMSCs, and that insufficiency of Mitofilin leads to BMMSC senescence and bone loss. More importantly, Mitofilin mediates resveratrol-induced mitochondrial and osteogenic improvements of BMMSCs in senescence.

Conclusion: Our findings uncover osteogenic functional improvements of senescent MSCs as critical impacts in anti-osteoporotic practice of RESV, and unravel Mitofilin as a novel mechanism mediating RESV promotion on mitochondrial function in stem cell senescence.

Lipopolysaccharide impairs permeability of pulmonary microvascular endothelial cells via Connexin40

The endotoxin lipopolysaccharide (LPS)-induced pulmonary endothelial barrier disruption is a key pathogenesis of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). However, the molecular mechanisms underlying LPS-impaired permeability of pulmonary microvascular endothelial cells (PMVECs) are not fully understood. Gap junctions, particularly Connexin40 (Cx40), are necessary for the maintenance of normal vascular function. In this study, we for the first time investigated the role of Cx40 in LPS-impaired permeability of PMVECs and provided potential therapeutic approaches based on mechanistic findings of Cx40 regulation by LPS stimuli. Rat PMVECs were isolated, cultured and identified with cell morphology, specific markers, ultrastructural characteristics and functional tests. Western blot analysis demonstrated that Cx40 is the major connexin highly expressed in PMVECs. Furthermore, by inhibiting Cx40 in a time-dependent manner, LPS impaired gap junction function and induced permeability injury of PMVECs. The key role of Cx40 decline in mediating detrimental effects of LPS was further confirmed in rescue experiments through Cx40 overexpression. Mechanistically, LPS stress on PMVECs inhibited the protein kinase C (PKC) pathway, which may synergize with the inflammatory nuclear factor kappaB (NFκB) signaling activation in suppressing Cx40 expression level and phosphorylation. Moreover, through pharmacological PKC activation or NFκB inhibition, Cx40 activity in PMVECs could be restored, leading to maintained barrier function under LPS stress. Our findings uncover a previously unrecognized role of Cx40 and its regulatory mechanisms in impaired endothelial integrity under endotoxin and inflammation, shedding light on intervention approaches to improve pulmonary endothelial barrier function in ALI and ARDS.

Stem cell-based bone regeneration in diseased microenvironments: Challenges and solutions

Restoration of extensive bone loss and defects remain as an unfulfilled challenge in modern medicine. Given the critical contributions to bone homeostasis and diseases, mesenchymal stem cells (MSCs) have shown great promise to jumpstart and facilitate bone healing, with immense regenerative potential in both pharmacology-based endogenous MSC rescue/mobilization in skeletal diseases and emerging application of MSC transplantation in bone tissue engineering and cytotherapy. However, efficacy of MSC-based bone regeneration was not always achieved; particularly, fulfillment of MSC-mediated bone healing in diseased microenvironments of host comorbidities remains as a major challenge. Indeed, impacts of diseased microenvironments on MSC function rely not only on the dynamic regulation of resident MSCs by surrounding niche to convoy pathological signals of bone, but also on the profound interplay between transplanted MSCs and recipient components that mediates and modulates therapeutic effects on skeletal conditions. Accordingly, novel solutions have recently been developed, including improving resistance of MSCs to diseased microenvironments, recreating beneficial microenvironments to guarantee MSC-based regeneration, and usage of subcellular vesicles of MSCs in cell-free therapies. In this review, we summarize state-of-the-art knowledge regarding applications and challenges of MSC-mediated bone healing, further offering principles and effective strategies to optimize MSC-based bone regeneration in aging and diseases.

Anti-aging pharmacology in cutaneous wound healing: effects of metformin, resveratrol, and rapamycin by local application

Cutaneous wounds are among the most common soft tissue injuries and are particularly hard to heal in aging. Caloric restriction (CR) is well documented to extend longevity; pharmacologically, profound rejuvenative effects of CR mimetics have been uncovered, especially metformin (MET), resveratrol (RSV), and rapamycin (RAPA). However, locally applied impacts and functional differences of these agents on wound healing remain to be established. Here, we discovered that chronic topical administration of MET and RSV, but not RAPA, accelerated wound healing with improved epidermis, hair follicles, and collagen deposition in young rodents, and MET exerted more profound effects. Furthermore, locally applied MET and RSV improved vascularization of the wound beds, which were attributed to stimulation of adenosine monophosphate-activated protein kinase (AMPK) pathway, the key mediator of wound healing. Notably, in aged skin, AMPK pathway was inhibited, correlated with impaired vasculature and reduced healing ability. As therapeutic approaches, local treatments of MET and RSV prevented age-related AMPK suppression and angiogenic inhibition in wound beds. Moreover, in aged rats, rejuvenative effects of topically applied MET and RSV on cell viability of wound beds were confirmed, of which MET showed more prominent anti-aging effects. We further verified that only MET promoted wound healing and cutaneous integrity in aged skin. These findings clarified differential effects of CR-based anti-aging pharmacology in wound healing, identified critical angiogenic and rejuvenative mechanisms through AMPK pathway in both young and aged skin, and unraveled chronic local application of MET as the optimal and promising regenerative agent in treating cutaneous wound defects.

Recipient Glycemic Micro-environments Govern Therapeutic Effects of Mesenchymal Stem Cell Infusion on Osteopenia

Therapeutic effects of mesenchymal stem cell (MSC) infusion have been revealed in various human disorders, but impacts of diseased micro-environments are only beginning to be noticed. Donor diabetic hyperglycemia is reported to impair therapeutic efficacy of stem cells. However, whether recipient diabetic condition also affects MSC-mediated therapy is unknown. We and others have previously shown that MSC infusion could cure osteopenia, particularly in ovariectomized (OVX) mice. Here, we discovered impaired MSC therapeutic effects on osteopenia in recipient type 1 diabetes (T1D). Through intensive glycemic control by daily insulin treatments, therapeutic effects of MSCs on osteopenia were maintained. Interestingly, by only transiently restoration of recipient euglycemia using single insulin injection, MSC infusion could also rescue T1D-induced osteopenia. Conversely, under recipient hyperglycemia induced by glucose injection in OVX mice, MSC-mediated therapeutic effects on osteopenia were diminished. Mechanistically, recipient hyperglycemic micro-environments reduce anti-inflammatory capacity of MSCs in osteoporotic therapy through suppressing MSC interaction with T cells via the Adenosine monophosphate-activated protein kinase (AMPK) pathway. We further revealed in diabetic micro-environments, double infusion of MSCs ameliorated osteopenia by anti-inflammation, attributed to the first transplanted MSCs which normalized the recipient glucose homeostasis. Collectively, our findings uncover a previously unrecognized role of recipient glycemic conditions controlling MSC-mediated therapy, and unravel that fulfillment of potent therapeutic effects of MSCs requires tight control of recipient micro-environments.

miR-21 deficiency inhibits osteoclast function and prevents bone loss in mice

MicroRNAs emerge as critical post-transcriptional regulators in bone metabolism. We have previously reported in vitro that miR-21 promotes osteogenesis, while studies have also revealed miR-21 as a regulator of osteoclastogenesis and a promoter of osteoclast differentiation in vitro. However, in vivo data are still lacking in identifying skeletal function of miR-21, particularly its effects on osteoporosis. Here, using miR-21 knockout (miR-21^-/-) mice, we investigated effects of miR-21 on bone development, bone remodeling and bone loss. Unexpectedly, miR-21^-/- mice demonstrated normal skeletal phenotype in development and maintained osteoblastogenesis in vivo. Besides, miR-21^-/- mice showed increased receptor activator of nuclear factor κB ligand (RANKL) and decreased osteoprotegerin (OPG) through miR-21 targeting Sprouty 1 (Spry1). Nevertheless, interestingly, miR-21 deficiency promoted trabecular bone mass accrual physiologically. Furthermore, in pathological states, the protection of bone mass was prominent in miR-21^-/- mice. These skeletal effects were attributed to inhibition of bone resorption and osteoclast function by miR-21 deficiency through miR-21 targeting programmed cell death 4 (PDCD4), despite the existence of RANKL. As far as we know, this is the first in vivo evidence of a pro-osteoclastic microRNA. Together, these findings clarified function of miR-21 in bone metabolism, particularly uncovering osteo-protective potential of miR-21 inactivation in osteoporosis.

Microenvironmental Views on Mesenchymal Stem Cell Differentiation in Aging

Aging is characterized by common environmental changes, such as hormonal, immunologic, and metabolic disorders. These pathologic factors impair the capability of mesenchymal stem cells (MSCs) to generate and maintain functionalized tissue components, contributing to age-related tissue degeneration (e.g., osteoporosis). However, in organismal aging, whether the microenvironmental signals induce common or differential MSC compromise and how they interact at the molecular level in mediating the functional decline of MSCs are not fully understood. In this review, we discuss the respective contribution of microenvironmental pathologic factors to age-related MSC dysfunction-particularly, the shifted differentiation from osteoblasts to adipocytes of bone marrow-derived MSCs. The authors summarize recent works regarding mechanisms underlying MSC-biased differentiation under altered microenvironments, which involve the activation of key signaling pathways, intracellular oxidative stress, and posttranscriptional regulations. In addition, we compare the differential influences of systemic and local microenvironments on MSC differentiation based on our findings. The authors also propose strategies to rescue differentiation disorders of MSCs in aging via modulating microenvironments, by using signaling modulators, anti-inflammatory agents, antioxidants, and metabolic regulators and by promoting mobilization of systemic MSCs to local injury sites. The authors hope that these insights contribute to MSC-based organismal aging research and treatments.

Site-specific function and regulation of Osterix in tooth root formation

Congenital diseases of tooth roots, in terms of developmental abnormalities of short and thin root phenotypes, can lead to loss of teeth. A more complete understanding of the genetic molecular pathways and biological processes controlling tooth root formation is required. Recent studies have revealed that Osterix (Osx), a key mesenchymal transcriptional factor participating in both the processes of osteogenesis and odontogenesis, plays a vital role underlying the mechanisms of developmental differences between root and crown. During tooth development, Osx expression has been identified from late embryonic to postnatal stages when the tooth root develops, particularly in odontoblasts and cementoblasts to promote their differentiation and mineralization. Furthermore, the site-specific function of Osx in tooth root formation has been confirmed, because odontoblastic Osx-conditional knockout mice demonstrate primarily short and thin root phenotypes with no apparent abnormalities in the crown (Journal of Bone and Mineral Research 30, 2014 and 742, Journal of Dental Research 94, 2015 and 430). These findings suggest that Osx functions to promote odontoblast and cementoblast differentiation and root elongation only in root, but not in crown formation. Mechanistic research shows regulatory networks of Osx expression, which can be controlled through manipulating the epithelial BMP signalling, mesenchymal Runx2 expression and cellular phosphorylation levels, indicating feasible routes of promoting Osx expression postnatally (Journal of Cellular Biochemistry 114, 2013 and 975). In this regard, a promising approach might be available to regenerate the congenitally diseased root and that regenerative therapy would be the best choice for patients with developmental tooth diseases.