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Photoreceptor apoptosis is recognized as one key pathogenesis of retinal degeneration, the counteraction of which represents a promising approach to safeguard visual function. Recently, mesenchymal stem cell transplantation (MSCT) has demonstrated immense potential to treat ocular disorders, in which extracellular vesicles (EVs), particularly exosomes, have emerged as effective ophthalmological therapeutics. However, whether and how MSCT protects photoreceptors against apoptotic injuries remains largely unknown. Here, we discovered that intravitreal MSCT counteracted photoreceptor apoptosis and alleviated retinal morphological and functional degeneration in a mouse model of photoreceptor loss induced by N-methyl-N-nitrosourea (MNU). Interestingly, effects of MSCT were inhibited after blockade of exosomal generation by GW4869 preconditioning. Furthermore, MSC-derived exosomal transplantation (EXOT) effectively suppressed MNU-provoked photoreceptor injury. Notably, therapeutic efficacy of MSCT and EXOT on MNU-induced retinal degeneration was long-lasting as photoreceptor preservance and retinal maintenance were detected even after 1–2 months post to injection for only once. More importantly, using a natural occurring retinal degeneration model caused by a nonsense mutation of Phosphodiesterase 6b gene (Pde6bmut), we confirmed that MSCT and EXOT prevented photoreceptor loss and protected long-term retinal function. In deciphering therapeutic mechanisms regarding potential exosome-mediated communications, we identified that miR-21 critically maintained photoreceptor viability against MNU injury by targeting programmed cell death 4 (Pdcd4) and was transferred from MSC-derived exosomes in vivo for functional regulation. Moreover, miR-21 deficiency aggravated MNU-driven retinal injury and was restrained by EXOT. Further experiments revealed that miR-21 mediated therapeutic effects of EXOT on MNU-induced photoreceptor apoptosis and retinal dysfunction. These findings uncovered the efficacy and mechanism of MSCT-based photoreceptor protection, indicating exosomal miR-21 as a therapeutic for retinal degeneration.

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., CD31hiEMCNhi 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.

Background: Mesenchymal stem cells (MSCs) have been used to treat immunopathy, and three-dimensional (3D) cultured MSCs show enhanced immunomodulatory property compared with those in two-dimensional (2D) culture. However, both the regulatory mechanisms remain unclear. The aim of the study was to investigate the role of mechanical stress in maintaining the immunomodulatory function of 2D and 3D cultured MSCs.Methods: Umbilical cord mesenchymal stem cells (UC-MSCs) were plated on tissue culture plastic (TCP) as 2D culture and 3D cultured UC-MSCs were seeded in matrigel. Surface markers, clonogenicity, proliferation and immunoregulatory property of UC-MSCs were evaluated. Meanwhile, we established the mouse models of colitis and type 1 diabetes mellitus (T1DM) to reveal the pharmacotherapeutic effects of 3D cultured MSCs in vivo. The effect of changing mechanical stress by modulating Yes-associated protein (YAP) on immunomodulatory function of 2D and 3D cultured UC-MSCs was evaluated by immunofluorescent analysis, real-time quantitative polymerase chain reaction (qPCR) and western blot.Results: We verified early passage UC-MSCs in 2D and 3D cultures exhibited stemness, immunomodulatory property and therapeutic efficacy against immunopathy. However, these characteristics of 2D cultured UC-MSCs were impaired after extensive expansion, whereas 3D culture extended them for several passages by activating YAP. Moreover, prostaglandin E2 (PGE2) could up-regulate YAP to improve the immunomodulatory ability of 2D cultured UC-MSCs after extensive expansion. Conclusions: This work found for the first time that the significance of mechanical stress in maintaining immunoregulatory function of 2D and 3D cultured UC-MSCs, providing a new idea for improving the efficacy of MSCs-based immunotherapy.

Summary 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., CD31hiEMCNhi 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., Highlights • Gli1+ cells regulate the neighbored specialized vessels in bone • Upon bone defect Gli1+ cells emerge and induce type H vessel formation for healing • Gli1+ cell ablation reduces type H vessels associated with suppressed osteogenesis • Gli and HIF-1α signaling mediate Gli1+ cell regulation of endothelial angiogenesis, In this article, Jin and colleagues show that skeletal Gli1+ cells represent a subpopulation of MSCs characterized by perivascular location, which spatially and phenotypically couple with a neighbored specialized vessel subtype, i.e., type H vessels. Functionally, Gli1+ cell-mediated regulation of type H vessel formation is indispensable for bone growth and regeneration.