Mechanosensory Channel Localization in Ultrasonography Targets Organs Involved in AKI Protection

Background: Ultrasound treatment of mouse kidneys or spleen protects mice from acute kidney injury (AKI) in renal ischemia-reperfusion injury (IRI) and lipopolysaccharide (LPS)-induced injury models. Using mutant mice with cell-type specific deletion of mechanosensory channels (MSC) in AKI models, we sought to determine whether Piezo1, Piezo2, and TrpV4 were key molecules that conferred ultrasound protection. To fully understand the mechanism of renal AKI protection by ultrasound, we studied the cellular distribution of these 3 MSCs in kidney and spleen. Methods: C57BL/6J mice undergoing AKI by IRI or LPS were treated with ultrasound and compared with appropriate controls. Serum creatinine, kidney histology, and mRNA expression of inflammatory genes were monitored at the end of experiments. Confocal microscopy of MSCs with cell-type specific markers were used for tissue distribution studies. Results: In the spleen, Piezo1 was expressed by macrophages in the red pulp and in the periarterial T cell zone. Piezo2 on the other hand was expressed by neuronal cells positive for tyrosine hydroxylase and neurofilament heavy chain. Some Piezo2+ nerve endings were found to be juxtaposed against the macrophage membrane. TrpV4 was expressed by F4/80+ macrophages and CD31+ endothelial cells. In the kidney, besides the expression of MSCs on cell types common between kidney and spleen, abundant MSCs were expressed on tubular epithelial cells. Piezo1 was expressed in descending thin limbs marked by Bst1, thick ascending limbs marked by THP, and connecting tubules and collecting ducts identified by Epcam and Claudin 7. In addition to its expression in distal tubules, TrpV4 was expressed by proximal tubules. Because ultrasound protection of LPS-induced AKI may be mediated by the activation of Nrf2 by Piezo1, the localization of Nrf2 in kidney was examined. The primary Nrf2 expressing kidney segment was the Bst1+ thin descending limb. These studies showed that kidney tubules may provide AKI protection by responding to ultrasound treatment through MSCs. Conclusion: The AKI protection of ultrasound may involve the complex interaction of MSC responses of multiple cell types including hematopoietic cells, neuronal cells, endothelial cells, and kidney tubular epithelial cells in spleen and kidney. Funding: NIDDK Support - NIDDK Support, NIDDK Support