Podocyte Injury and Glomerular Inflammation Induced by Urinary Exosomes from Hyperhomocysteinemic Mice

Abstract

Hyperhomocysteinemia (hHcy) has been demonstrated to induce NLRP3 inflammasome activation and inflammatory exosome release in podocytes of mice, which can be enhanced by podocyte-specific Smpd1 gene overexpression or blocked by global Smpd1 gene deletion. However, it remains unknown whether hHcy-induced podocyte injury and glomerular inflammation are attributed to these exosomes secreted from podocytes during hHcy. In the present study, we found that exosomes extracted from urine of mice with hHcy induced by folate free (FF) diet induced podocyte injury when they were infused into the renal cortical interstitial space in both WT/WT and Smpd1-/- mice, as shown by reduction of podocin and elevation of desmin in glomeruli. These exosomes from mice with hHcy also increased T-cells in glomeruli, which was not blocked by global Smpd1 gene deletion. Functionally, proteinuria was detected in both WT/WT and Smpd1-/- mice receiving these exosomes from mice with hHcy. However, infusion of urinary exosomes from mice on the normal diet (ND) had no effects on these podocyte injury and glomerular inflammatory changes. We also performed in vitro experiments with cultured podocytes. We treated murine podocytes with urinary exosomes from mice on the ND and FF diet. It was found that exosomes from mice on the FF diet produced no significant effects on podocytes compared with control exosomes if they were cultured without immune cells. If murine podocytes were co-cultured with T-cells, macrophages, or both, the exosomes from mice with hHcy caused significant podocyte damage as shown by reduction of podocin and elevation of desmin, but exosomes from mice on the ND failed to influence podocytes even in the presence of immune cells. These results suggest that hHcy increases urinary exosomes and these exosomes importantly contribute to podocyte injury and glomerular inflammation during hHcy.