Ionomycin ameliorates hypophosphatasia via rescuing alkaline phosphatase deficiency-mediated L-type Ca^(2+) channel internalization in mesenchymal stem cells

The loss-of-function mutations in the ALPL result in hypophosphatasia(HPP), an inborn metabolic disorder that causes skeletal mineralization defects. In adults, the main clinical features are early loss of primary or secondary teeth, osteoporosis, bone pain,chondrocalcinosis, and fractures. However, guidelines for the treatment of adults with HPP are not available. Here, we show that ALPL deficiency caused a reduction in intracellular Ca2+ influx, resulting in an osteoporotic phenotype due to downregulated osteogenic differentiation and upregulated adipogenic differentiation in both human and mouse bone marrow mesenchymal stem cells(BMSCs). Increasing the intracellular level of calcium in BMSCs by ionomycin treatment rescued the osteoporotic phenotype in alpl+/- mice and BMSC-specific(Prrx1-alpl-/-) conditional alpl knockout mice. Mechanistically, ALPL was found to be required for the maintenance of intracellular Ca2+ influx, which it achieves by regulating L-type Ca2+ channel trafficking via binding to the α2δsubunits to regulate the internalization of the L-type Ca2+ channel. Decreased Ca2+ flux inactivates the Akt/GSK3β/β-catenin signaling pathway, which regulates lineage differentiation of BMSCs. This study identifies a previously unknown role of the ectoenzyme ALPL in the maintenance of calcium channel trafficking to regulate stem cell lineage differentiation and bone homeostasis. Accelerating Ca2+ flux through L-type Ca2+ channels by ionomycin treatment may be a promising therapeutic approach for adult patients with HPP.

Mechanical force-driven TNFαendocytosis governs stem cell homeostasis

Mesenchymal stem cells(MSCs)closely interact with the immune system,and they are known to secrete inflammatory cytokines in response to stress stimuli.The biological function of MSC-derived inflammatory cytokines remains elusive.Here,we reveal that even under physiological conditions,MSCs produce and release a low level of tumor necrosis factor alpha(TNFα),which is unexpectedly required for preserving the self-renewal and differentiation of MSCs via autocrine/paracrine signaling.Furthermore,TNFαcritically maintains MSC function in vivo during bone homeostasis.Mechanistically,we unexpectedly discovered that physiological levels of TNFαsafeguard MSC homeostasis in a receptor-independent manner through mechanical force-driven endocytosis and that endocytosed TNFαbinds to mammalian target of rapamycin(mTOR)complex 2 and restricts mTOR signaling.Importantly,inhibition of mTOR signaling by rapamycin serves as an effective osteoanabolic therapeutic strategy to protect against TNFαdeficiency and mechanical unloading.Collectively,these findings unravel the physiological framework of the dynamic TNFαshuttlebased mTOR equilibrium that governs MSC and bone homeostasis.

Immunomodulatory properties of mesenchymal stem cells/dental stem cells and their therapeutic applications

Mesenchymal stem/stromal cells(MsCs)are widely distributed in the body and play essential roles in tissue regeneration and homeostasis.MsCs can be isolated from discarded tissues,expanded in vitro and used as therapeutics for autoimmune diseases and other chronic disorders.MsCs promote tissue regeneration and homeostasis by primarily acting on immune cells.At least six different types of MsCs have been isolated from postnatal dental tissues and have remarkable immunomodulatory properties.Dental stem cells(DsCs)have been demonstrated to have therapeutic effects on several systemic inflammatory diseases.Conversely,MsCs derived from nondental tissues such as the umbilical cord exhibit great benefits in the management of periodontitis in preclinical studies.Here,we discuss the main therapeutic uses of MSCs/DSCs,their mechanisms,extrinsic inflammatory cues and the intrinsic metabolic circuitries that govern the immunomodulatory functions of MSCs/DSCs.Increased understanding of the mechanisms underpinning the immunomodulatory functions of MSCs/DSCs is expected to aid in the development of more potent and precise MSC/DSC-based therapeutics.

Apoptotic vesicles ameliorate lupus and arthritis via phosphatidylserine-mediated modulation of T cell receptor signaling

Mesenchymal stem cells(MSCs)influence T cells in health,disease and therapy through messengers of intercellular communication including extracellular vesicles(EVs).Apoptosis is a mode of cell death that tends to promote immune tolerance,and a large number of apoptotic vesicles(apoVs)are generated from MSCs during apoptosis.In an effort to characterize these apoVs and explore their immunomodulatory potential,here we show that after replenishing them systemically,the apoV deficiency in Fas mutant mice and pathological lymphoproliferation were rescued,leading to the amelioration of inflammation and lupus activity.ApoVs directly interacted with CD4^(+)T cells and inhibited CD25 expression and IL-2 production in a dose-dependent manner.A broad range of Th1/2/17 subsets and cytokines including IFNγ,IL17A and IL-10 were suppressed while Foxp3^(+)cells were maintained.Mechanistically,exposed phosphatidylserine(PtdSer/PS)on apoVs mediated the interaction with T cells to disrupt proximal T cell receptor signaling transduction.Remarkably,administration of apoVs prevented Th17 differentiation and memory formation,and ameliorated inflammation and joint erosion in murine arthritis.Collectively,our findings unveil a previously unrecognized crosstalk between MSC apoVs and CD4^(+)T cells and suggest a promising therapeutic use of apoVs for autoimmune diseases.

Apoptotic vesicles rejuvenate mesenchymal stem cells via Rab7-mediated autolysosome formation and alleviate bone loss in aging mice

Aging skeletons display decreased bone mass,increased marrow adiposity,and impaired bone marrow mesenchymal stem cells(MSCs).Apoptosis is a programmed cell death process that generates a large number of apoptotic vesicles(apoVs).Dysregulated apoptosis has been closely linked to senescence-associated diseases.However,whether apoVs mediate agingrelated bone loss is not clear.In this study,we showed that young MSC-derived apoVs effectively rejuvenated the nuclear abnormalities of aged bone marrow MSCs and restored their impaired self-renewal,osteo-/adipo-genic lineage differentiation capacities via activating autophagy.Mechanistically,apoptotic young MSCs generated and enriched a high level of Ras-related protein 7(Rab7)into apoVs.Subsequently,recipient aged MSCs reused apoV-derived Rab7 to restore autolysosomes formation,thereby contributing to autophagy flux activation and MSC rejuvenation.Moreover,systemic infusion of young MSC-derived apoVs enhanced bone mass,reduced marrow adiposity,and recused the impairment of recipient MSCs in aged mice.Our findings reveal the role of apoVs in rejuvenating aging-MSCs via restoring autolysosome formation and provide a potential approach for treating age-related bone loss.

Apoptotic extracellular vesicles are metabolized regulators nurturing the skin and hair

Over 300 billion of cells die every day in the human body,producing a large number of endogenous apoptotic extracellular vesicles(apoEVs).Also,allogenic stem cell transplantation,a commonly used therapeutic approach in current clinical practice,generates exogenous apoEVs.It is well known that phagocytic cells engulf and digest apoEVs to maintain the body’s homeostasis.In this study,we show that a fraction of exogenous apoEVs is metabolized in the integumentary skin and hair follicles.Mechanistically,apoEVs activate the Wnt/β-catenin pathway to facilitate their metabolism in a wave-like pattern.The migration of apoEVs is enhanced by treadmill exercise and inhibited by tail suspension,which is associated with the mechanical force-regulated expression of DKK1 in circulation.Furthermore,we show that exogenous apoEVs promote wound healing and hair growth via activation of Wnt/β-catenin pathway in skin and hair follicle mesenchymal stem cells.This study reveals a previously unrecognized metabolic pathway of apoEVs and opens a new avenue for exploring apoEV-based therapy for skin and hair disorders.