Role of nonmuscle myosin IIA in sex-dependent failed repair mechanisms in acute kidney injury

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ABSTRACT The cellular mechanisms that drive the progression of acute kidney injury (AKI) to chronic kidney disease (CKD) are not well understood. AKI is the abrupt decrease of kidney function from a variety of causes that elicits structural and functional damage. The prevalence of AKI is increasing rapidly in the United States and presents a healthcare burden worldwide. To date, there are no effective therapies for the mitigation of the proinflammatory and fibrotic phenotypes resulting from injury. Interestingly, it has been recently supported with epidemiological data that female sex is a protective factor in the AKI progression to CKD. Leveraging the comparison of sex specific mechanisms in ischemic injury has incredible potential for the identification of novel, effective therapeutic targets. Therefore, I will be employing single nuclei RNA and ATAC-Sequencing, as well as spatial transcriptomics to generate a multimodal atlas of the injury time course in females undergoing bilateral ischemia reperfusion injury (Bi-IRI). Recently, a novel cell state has been identified in male mice following Bi-IRI using single nuclei RNA sequencing. Known as failed repair proximal tubule cells (FR-PTC), these cells represent a dead end in the recovery pathway and could be lending a role to increases in proliferation, fibrosis, and inflammation that worsen kidney tissue after injury. These FR-PTCs exhibit a profile of differentially expressed genes that are unique from healthy and repairing cell states. One of these genetic markers, which is also a genome wide association study (GWAS) gene associated with CKD, was Myh9. Myh9 expression is upregulated specifically in injured and failed repair cell clusters, and is found in low levels in healthy and repairing proximal tubule cells. This gene encodes for nonmuscle myosin IIA (NMIIA), which plays an important role in cell shape, adhesion, migration, and cytokinesis. It interacts directly with actin, creating a stable cytoskeletal network. Drastic changes in Myh9 expression may translate into changes in NMIIA abundance that could alter the regulation of downstream signaling, contributing to phenotypes characteristic of AKI. Therefore, I hypothesize that sexually dimorphic expression of Myh9 in the kidney and sex-specific mechanisms of NMIIA activation contribute to the renoprotection of female sex. Preliminary data suggests that female C57BL/6J mice at baseline have higher expression of Myh9 than males, potentially indicating that females have developed mechanisms for decreasing activity of NMIIA through downregulation of ischemia responsive kinases. This proposal will investigate these expression changes in males and females along the injury time course following Bi-IRI using single nuclei sequencing and spatial transcriptomics. Additionally, the relationship between ischemia and NMIIA function will be investigated using gold standard biochemical techniques in in vivo and in vitro cell models. Ultimately, this proposal will generate a transcriptomic atlas of sex differences in AKI and illuminate the role of NMIIA in the disease progression of AKI to CKD, potentially identifying a new sex-specific therapeutic target.