Novel macula densa mechanisms of salt-sensitive hypertension
Authors: Shroff Urvi Nikhil , Gyarmati Georgina , Deepak Sachin , Izuhara Audrey , Peti-Peterdi Janos 
Published: May 2023

Salt-sensitive hypertension (SSH) is a highly prevalent disease condition, affecting millions of people each year. Elevated blood pressure (BP) characteristic of SSH results in the development of albuminuria, tissue fibrosis, inflammation, and eventually decline in kidney function. In particular, immune cell infiltration plays a central role in the progression of SSH; however, the mechanism driving the infiltration is poorly understood. Macula densa (MD) cells, the tubular component of the juxtaglomerular apparatus, are chief salt sensors located in the distal nephron, and play a critical role in the salt-dependent regulation of renal hemodynamics, glomerular filtration rate, and renin release. Interestingly, recent observations from our laboratory have highlighted the important role of MD protein synthesis activity and its paracrine effect on glomerular function. The current study focuses on understanding the regulatory role of MD cells in driving immune cell infiltration in the context of SSH via the release of paracrine acting chemokines and cytokines. We found that MD cells have the highest protein synthesis activity in the kidney cortex, including the chemotactic factors and cytokines CxCl14, CCN1, and CCN3. Bulk and single-cell RNA sequencing data of MD cells corroborated high expression of both pro- ( CxCl14, Ptges, etc.) and anti-inflammatory ( Ccn1, Mif, etc.) genes. Using the newly established immortalized MD cell line mMDGeo and immunoblotting, high salt (HS) treatment (200 mM NaCl vs 150 mM in control) resulted in significantly lower expression of anti-inflammatory peptide CCN1. In order to alter MD protein synthesis activity, we developed MD-specific, inducible genetic gain/loss-of-function (gof/lof) mTOR signaling mouse models (MD-mTOR gof/lof ). Control wildtype (WT) and MD-mTOR gof/lof mice were placed on a 2-week HS diet with BP measurements at baseline and after HS diet. Treatment with HS diet for two weeks resulted in significant elevation in systolic BP in MD-mTOR lof mice (133 mm Hg vs 107 mm Hg in WT control) with no significant change in MD-mTOR gof mice. Multiphoton imaging was employed to track fluorescently labeled endogenous immune cell populations in vivo, including T cells (PE-CD44) and macrophages (Alexa488-CD11b), via 10 minute xyzt scans of multiple glomeruli. MD-mTOR lof mice displayed significantly higher number of glomerular CD11b+ macrophages (6.1 vs 2.4 cells/glom in WT control) and CD44+ T cells (21.8 vs 11.5 cells/glom in WT control) after HS treatment, with MD-mTOR gof mice showing the opposite effect. Taken together, these results suggest a new regulatory role of MD-derived cytokines and chemokines in glomerular immune cell infiltration in the context of SSH. These newly uncovered mechanisms can be potentially targeted in the future to develop anti-inflammatory therapeutic strategies for kidney disease. NIDDK, AHA This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.