Macula densa cells control glomerular immune cell homing

Abstract

Circulating and kidney resident immune cells preferentially home in and around the glomerulus compared to other vascular beds in both normal and inflammatory states, suggesting the presence of unique antimicrobial mechanisms in the glomerular microcirculation that protect the kidney filter. However, the underlying cell and molecular mechanisms are largely unknown. Macula densa (MD) cells are localized at the glomerular vascular entrance as a unique juxtaglomerular cell type and are known to control glomerular hemodynamics, and more recently, glomerular tissue remodeling. This study addressed the hypothesis that MD cells control glomerular immune cell homing by the release of paracrine‐acting pro‐inflammatory factors including opsonins, cytokines, and lymphokines. Bulk and single cell RNA sequencing and transcriptomic analysis of MD vs. control cells isolated from MD‐GFP mouse kidneys identified the high MD‐enrichment of several pathways and genes in the inflammatory response and cellular infiltration by leukocytes (Lcn2, Fga, Fgg, Casp4, Ptgs2, Ptges, Anxa1, Spns2, Spp1, Clu, Ccn1, Cxcl14, Mif). Mice with MD‐specific gain‐of‐function of mTOR (MD‐mTORgof) were developed by intercrossing nNOS/Cre and TSC2/fl mice, and feature globally increased MD cell protein synthesis. Immunoblotting of kidney cortex homogenates confirmed the significant increase in the expression of MD‐specific Ccn1, Cxcl14, Ptgs2, and Ptges in MD‐mTORgof vs. control mice. Intravital multiphoton imaging of the kidney cortex and endogenous circulating and kidney resident immune cell populations (labeled with anti‐CD44‐Alexa680 and F4/80‐Alexa488 antibodies) observed the significantly increased glomerular number, transit time, and migration of circulating CD44+ immune cells and tissue macrophages in MD‐mTORgof vs. control mice. NZM.2328 lupus mice featured significantly increased MD‐centric glomerular density and migration of CD8+ T cells. These results suggest the new role of MD cells and several MD‐derived paracrine‐acting molecular factors as important control mechanisms of glomerular inflammation in health and disease conditions. These newly identified MD mechanisms may be targeted in future anti‐inflammatory therapeutic strategies.