Small Extracellular Vesicles Derived From Damaged Muscle Aggravate Kidney Injury Progression.

backgroundMuscle atrophy is commonly associated with kidney dysfunction in patients with renal disease. However, the effects of skeletal muscle loss per se on kidney function have not been fully elucidated. Here, we examined muscle-kidney crosstalk by evaluating the role of muscle-derived small extracellular vesicles (EVs) on the progression of kidney injury.

methodsA denervation-induced muscle loss model was established, and kidney inflammation and fibrosis were evaluated in unilateral ureteral obstruction (UUO)-induced kidney injury and adenine diet-induced chronic kidney disease models. Changes in small EV markers (CD9, CD63, CD81 and Alix) were measured. GW4869, an inhibitor of EV biogenesis and release, was used to confirm the role of denervated muscle-derived small EVs on the progression of kidney fibrosis. To obtain direct evidence on the crosstalk, EVs were isolated from plasma of denervated mice and conditioned media from differentiated myotubes and treated in vivo and in vitro. To determine the effect of exercise-induced EVs on kidney fibrosis, EVs isolated from exercised mice and trained humans were treated to TGFβ1-stimulated mProx24 renal tubular epithelial cells.

resultsDenervation aggravated kidney injury, as shown by a 10% increase in albuminuria and upregulation of inflammatory and fibrotic markers in the kidney. Significant interactions between denervation and UUO were observed for renal αSMA (F = 47.19, p < 0.0001) and FN (F = 19.06, p = 0.0001) expression. EV production and secretion were markedly increased in damaged muscle, both in vivo and in vitro. Pharmacological depletion of EVs using GW4869 via intraperitoneal and intramuscular injection reduced kidney injury by over 20%. Furthermore, injection of EVs from denervated muscle into UUO mice, as well as treatment of mProx24 cells with EVs from either denervated mice or damaged C2C12 myotubes, significantly amplified renal injury. Among the EV cargo, miR-21a-3p-identified as a regulator of Ppargc1a-was elevated over 10-fold in EVs from denervated muscle compared with sham controls. Importantly, EV-induced injury in mProx24 cells was reversed by pretreatment with a miR-21a inhibitor. In contrast, exercise downregulated miR-21a-3p expression in muscle, and EVs derived from exercised mice and humans attenuated kidney fibrosis.

conclusionsOur findings provide novel evidence that skeletal muscle loss can serve as an upstream contributor to kidney disease. Muscle-derived EVs from damaged tissue exacerbate, while those from exercised muscle ameliorate, kidney injury, partly through miR-21a-3p regulation. These results highlight the critical role of miRNAs within muscle-derived EVs in maintaining kidney homeostasis and suggest their potential as therapeutic targets.