G-MDSC derived LETS1 promotes mesenchymal stem cell differentiation into myofibroblasts via targeting TGF Beta Receptor I in renal fibrosis

Introduction: Renal fibrosis is a common pathological endpoint in various acute and chronic kidney diseases, characterized by myofibroblast activation and excessive deposition of extracellular matrix. Following ischemia-reperfusion injury (IRI) in transplanted kidneys, the repair phase establishes a local "fibrotic niche" that provides a microenvironment conducive to myofibroblast activation. During the early stage of injury, undifferentiated mesenchymal stem cells (MSCs) exert anti-inflammatory functions; in later stages, however, they proliferate and differentiate into myofibroblasts, thereby promoting renal fibrosis. Our previous studies revealed that M-MDSCs modulate the immunosuppressive function of MSCs during the acute inflammatory phase and early fibrotic formation, whereas G-MDSCs exhibit spatiotemporal differences and facilitate the progression of renal fibrosis. The underlying mechanisms remain to be fully elucidated.
Methods: In vivo, a mouse model of unilateral renal ischemia-reperfusion injury was used to induce renal fibrosis. Histopathological staining, including hematoxylin and eosin, Sirius red, and immunofluorescence, was performed to assess the degree of renal fibrosis and the distribution of MSCs in kidney tissues at different time points after IRI. Flow cytometry was employed to examine changes in the subpopulations of G-MDSCs and M-MDSCs at these time points. In the later phase of injury, G-MDSCs were depleted by anti-Gr1 antibody injection to evaluate their effect on renal fibrosis. In vitro, co-culture systems, exosome inhibition assays, quantitative PCR, Western blot, and lncRNA sequencing were conducted to analyze the regulatory role of G-MDSCs in MSC differentiation and the associated molecular mechanisms.
Results: Our study demonstrated that during the repair phase (days 7–28) after IRI, the number of G-MDSCs increased significantly and surpassed that of M-MDSCs. Depletion of G-MDSCs markedly attenuated renal fibrosis and reduced the expression of α-SMA and extracellular matrix-related proteins. In vitro co-culture experiments indicated that G-MDSCs promoted the expression of TβRⅠ and phosphorylation of SMAD2/3 in MSCs via exosomes, thereby enhancing the activity of the TGF-β signaling pathway. LncRNA sequencing revealed that lncRNA LETS1 was significantly upregulated in exosomes derived from G-MDSCs. LncRNA LETS1 could bind to and stabilize TβRⅠ, facilitating the differentiation of MSCs into myofibroblasts. Inhibition of exosome release or lncRNA LETS1 expression substantially attenuated these effects.
Conclusion: This study reveals that in the later stage of kidney injury, G-MDSCs promote the differentiation of MSCs into myofibroblasts and the progression of renal fibrosis by delivering exosomal lncRNA LETS1, which enhances TβRⅠ stability and activates the TGF-β/SMAD2/3 signaling pathway. Targeting G-MDSCs or exosomal lncRNA LETS1 may offer a novel therapeutic strategy for delaying or reversing renal fibrosis.