Meprin β activity modulates cellular proliferation via trans-signaling IL-6-mediated AKT/ERK pathway in IR-induced kidney injury.

Inflammation plays a central role in the progression of kidney injury induced by ischemia/reperfusion (IR). Meprin metalloproteinases have been implicated in the pathophysiology of IR-induced kidney injury. Existing data from in vitro and in vivo studies show that meprins modulate interleukin-6 (IL-6)-mediated inflammation via proteolytic processing of IL-6 and its receptor. IL-6 trans-signaling induces proliferation through either MAPK/ERK or PI3K/AKT pathway or in crosstalk with AKT/ERK. We previously showed that meprin β modulates cellular survival (BCL-2) through IL-6/JAK/STAT signaling pathway in IR-induced kidney injury. However, it's not known how meprin β modulation of the IL-6 signaling pathway impacts the cellular proliferation in IR-induced acute kidney injury. The goal of the current study was to determine how meprin β modulation of the IL-6 signaling pathway impacts downstream cellular proliferation in IR-induced kidney injury. We used the unilateral IR as a model of renal inflammation in wild-type (WT) and meprin β knockout (βKO) mice, with the contralateral kidneys serving as controls. The mice were sacrificed at 96 h post-IR, and kidney tissue processed for evaluation by RT-PCR and immunohistochemistry. Statistical analysis utilized two-way ANOVA. RT-PCR data showed a significant increase in mRNA levels for IL-6 and proliferating cell nuclear antigen (PCNA) in WT and βKO mice at 96 h-post IR when compared to WT control kidneys. However, the baseline mRNA levels for PCNA were significantly higher in βKO when compared to WT kidneys. Immunohistochemical data showed significant increases in IL-6, PCNA, p-AKT and p-ERK in select tubules in both genotypes at 96 h post-IR when compared to control kidneys for each genotype. Data from immunofluorescence counterstaining of kidney tissues revealed that at 96 hours post-IR, IL-6, PCNA, p-AKT, and p-ERK were primarily expressed in meprin β-expressing proximal tubules (PTs), where meprins are abundantly present. However, high levels of IL-6 were also present in the lumen of PTs and DTs from WT and βKO kidneys at 96 h post-IR, suggesting increased release/shedding into filtrate and subsequently into urine. In conclusion, this study highlights the role of meprin β activity in regulating cellular proliferation through PCNA regulation, driven by the IL-6-mediated AKT/ERK signaling pathway during the recovery phase following IR-induced kidney injury.