Nrp-1 Mediated Plasmatic Ago2 Binding miR-21a-3p Internalization: A Novel Mechanism for miR-21a-3p Accumulation in Renal Tubular Epithelial Cells during Sepsis

The mechanism underlying sepsis-associated acute kidney injury (SAKI), which is an independent risk factor for sepsis-associated death, is unclear. A previous study indicates that during sepsis miR-21a-3p accumulates in renal tubular epithelial cells (TECs) as the mediator of inflammation and mediates TEC malfunction by manipulating its metabolism. However, the specific mechanism responsible for the accumulation of miR-21a-3p in TECs during sepsis is unrevealed. In this study, a cecal ligation and puncture- (CLP-) induced sepsis rat model and rat TEC line were used to elucidate the mechanism. Firstly, miR-21a-3p and Ago2 levels were found out to increase in both plasma and TECs during sepsis, and the increase of intracellular Ago2 and miR-21a-3p could be mitigated when Ago2 was either inactivated or downregulated in septic plasma. Moreover, membrane Nrp-1 expression of TECs was increased significantly during sepsis and Nrp-1 knockdown also mitigated the rise of both the intracellular Ago2 and miR-21a-3p levels in TECs incubated with septic plasma. Furthermore, it was revealed that Ago2 can be internalized by TECs mediated with Nrp-1 and this process had no effect on the intracellular content of miR-21a-3p. Both Ago2 and miR-21a-3p could bind to TECs derived Nrp-1 directly. Finally, it was determined that miR-21a-3p was internalized by TECs via Nrp-1 and Ago2 facilitated this process. Taken together, it can be concluded from our results that Ago2 binding miR-21a-3p from septic plasma can be actively internalized by TECs via Nrp-1 mediated cell internalization, and this mechanism is crucial for the rise of intracellular miR-21a-3p content of TECs during sepsis. These findings will improve our understanding of the mechanisms underlying SAKI and aid in developing novel therapeutic strategies.