Mapping Lipid Signatures Among Glomerular Cell Types: Spatiomolecular Insights into Normal and Diseased Tissue Microenvironments

Abstract

The kidney is made of approximately one million nephrons, which execute vital functions such as blood filtration, electrolyte balance, and urine production. Each nephron begins with a glomerulus, which is a spherical structure that is essential for filtering blood through the coordination of four specialized cell types (podocytes, mesangial cells, epithelial cells, and fenestrated endothelial cells). Kidney diseases, such as diabetic kidney disease (DKD) and chronic kidney disease (CKD), can cause alterations in the glomerular cells by inducing podocyte loss, thickening of the glomerular basement membrane, and mesangial cell expansion. Furthering our understanding of molecular distributions among healthy glomerular cell types and the spatiomolecular changes that occur as a result of diseases that can lead to CKD and DKD, such as hypertension and type 2 diabetes (T2D), is crucial for elucidating mechanisms underlying chronic kidney diseases. Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) is a powerful technology to map molecular distributions in tissue sections at high spatial resolution. This study presents a workflow combining MALDI IMS with multiplexed immunofluorescence (MxIF) to investigate lipid heterogeneity among cell types in glomeruli from normal, hypertensive, and T2D patients. By utilizing interpretable supervised machine learning, we uncovered distinct lipid biomarker candidates associated with individual glomerular cell types. For example, sphingomyelin (SM) (34:1;O2) was found to be positively correlated to podocytes in negative and positive ionization modes. These results were demonstrated to be robust across multiple patients and with the use of two distinct MxIF techniques using different antibodies for glomeruli. Cellular-level lipidomic changes were uncovered when comparing patients with hypertension or T2D to controls, indicating disease-induced cellular and mitochondrial membrane alterations. This integrated workflow enables a comprehensive examination of molecular profiles, which can advance our understanding of how conditions, such as hypertension and T2D, alter renal cell function and contribute to CKD and DKD progression.