Macrophage ITGAM Aggravates Diabetic Kidney Disease Through Modulating Lipolysis and Immune-Inflammatory Responses Introduction

Diabetic kidney disease (DKD) is one of the most common microvascular complications of diabetes and the leading cause of end-stage renal disease. Chronic low-grade inflammation is considered one of the key factors driving the progression of DKD. Immune dysregulation within the diabetic microenvironment, particularly alterations in macrophage metabolism and function, constitutes a principal driver of the inflammatory response. ITGAM (Integrin Alpha M), a member of the integrin family, is predominantly expressed on macrophages and modulates their polarization. However, the mechanism through which ITGAM modulates macrophage lipid metabolism and promotes DKD progression remains elusive. Therefore, systematically deciphering the mechanisms of immunometabolism in macrophages is of great significance.

Renal samples were collected from patients with biopsy-confirmed diabetic nephropathy, while control samples were obtained from non-tumor kidney tissues during nephrectomy. Immunohistochemistry and fluorescence assays were performed to detect ITGAM expression levels and cellular localization. Peripheral blood mononuclear cells (PBMCs) were obtained from diabetic patients to examine ITGAM expression levels in relation to the degree of proteinuria. We subsequently established diabetic mouse models using both macrophage-specific Itgam knockout and overexpression mice, and evaluated the efficacy of an anti-ITGAM neutralizing antibody in db/db mice. Tissue injury and inflammatory cell infiltration were assessed, along with macrophage polarization and renal lipid droplet distribution. Single-cell RNA sequencing was integrated to precisely identify macrophage subtypes and analyze intercellular communication. In vitro, primary macrophages were used to investigate the effect of ITGAM on lipid droplet distribution and lipolysis. Co-immunoprecipitation coupled with mass spectrometry was employed to identify ubiquitination modifications of ATGL protein, while fluorescent fatty acids were used to visualize lipolysis and mitochondrial localization.

We found that ITGAM was highly expressed in macrophages within the DKD, both in patients and mouse models. Urinary proteomic analysis of diabetic patients revealed significantly increased urinary ITGAM excretion in DKD patients, and the urinary ITGAM-to-creatinine ratio rose with worsening proteinuria. Both macrophage-specific Itgam knockout mice and administration of an ITGAM-neutralizing antibody alleviated renal macrophage lipid metabolic disturbances and mitochondrial dysfunction. Conversely, Itgam overexpression models exhibited increased proteinuria and lipotoxicity. Mechanistic investigations demonstrated that ITGAM promotes peroxin 2-mediated ubiquitination and degradation of ATGL. ITGAM deficiency or inhibition restored fatty acid mobilization by preventing ATGL ubiquitination, thereby attenuating lipid droplet accumulation and inflammation following DKD. These findings indicate that ITGAM is critical for maintaining macrophage lipid homeostasis.

Our study pinpoints ITGAM as a pivotal regulator of macrophage lipid homeostasis in DKD from an immunometabolic perspective, paving the way for a viable immunotherapy strategy.