Kidney resident macrophages have distinct subsets and multifunctional roles

Abstract

Background: The kidney contains distinct glomerular and tubulointerstitial compartments with diverse cell types and extracellular matrix components. The role of immune cells in glomerular environment is crucial for dampening inflammation and maintaining homeostasis. Macrophages are innate immune cells that are influenced by their tissue microenvironment. However, the multifunctional role of kidney macrophages remains unclear.

Methods: Flow and imaging cytometry were used to determine the relative expression of CD81 and CX₃CR1 (C-X3-C motif chemokine receptor 1) in kidney macrophages. Monocyte replenishment was assessed in Cx3cr1^CreER X R26-yfp-reporter and shielded chimeric mice. Bulk RNA-sequencing and mass spectrometry-based proteomics were performed on isolated kidney macrophages from wild type and Col4a5^-/- (Alport) mice. RNAscope was used to visualize transcripts and macrophage purity in bulk RNA assessed by CIBERSORTx analyses.

Results: In wild type mice we identified three distinct kidney macrophage subsets using CD81 and CX₃CR1 and these subsets showed dependence on monocyte replenishment. In addition to their immune function, bulk RNA-sequencing of macrophages showed enrichment of biological processes associated with extracellular matrix. Proteomics identified collagen IV and laminins in kidney macrophages from wild type mice whilst other extracellular matrix proteins including cathepsins, ANXA2 and LAMP2 were enriched in Col4a5^-/- (Alport) mice. A subset of kidney macrophages co-expressed matrix and macrophage transcripts.

Conclusions: We identified CD81 and CX₃CR1 positive kidney macrophage subsets with distinct dependence for monocyte replenishment. Multiomic analysis demonstrated that these cells have diverse functions that underscore the importance of macrophages in kidney health and disease.

Keywords: Basement membrane; Cytometry; Extracellular matrix; Kidney; Macrophages; Proteomics; RNA-sequencing.