Exposure to MC-LR activates the RAF/ERK signaling pathway, leading to renal inflammation and tissue damage in mice.

Exposure to microcysatin-LR (MC-LR) is known to result in kidney damage, however the underlying mechanisms involved in MC-LR-initiated renal injury are not known. Thus, the aim of this study was to examine the effects of exposure to MC-LR on human embryo kidney (HEK 293) cell in vitro and male C57BL/6 in vivo. In the in vitro study, HEK 293 cells were incubated with MC-LR (20 µM) for 24 hr. Treatment with MC-LR significantly increased the protein expression of RAF and ERK as well as mRNA expression levels of inflammatory cytokines TNF-α, IL-6, and IL-1β. These findings were confirmed when HEK 293 cells were co-incubated with ERK inhibitor U0126 and MC-LR demonstrating a decrease in protein expression of RAF, ERK, and mRNA levels of pro-inflammatory cytokines. Male C57BL/6 mice were intraperitoneally (ip) injected with MC-LR (20 µg/kg) daily for 21 days. Histopathological analysis demonstrated significant glomerular and tubular damage with inflammatory infiltration. The expression levels of pro-inflammatory cytokines TNF-α, IL-6, and IL-1β were significantly elevated following MC-LR treatment. Administration of MC-LR asignificantly enhanced the protein phosphorylation levels of RAF and ERK. Data demonstrated that exposure to MC-LR induced morphological tissue damage and renal inflammatory reactions by activating the RAF/ERK signaling pathway.