Abstract
Proximal tubular epithelial cells (PTEC) are central players in inflammatory kidney diseases. However, the complex signalling mechanism/s via which polarized PTEC mediate disease progression are poorly understood. Small extracellular vesicles (sEV), including exosomes, are recognized as fundamental components of cellular communication and signalling courtesy of their molecular cargo (lipids, microRNA, proteins). In this study, we examined the molecular content and function of sEV secreted from the apical versus basolateral surfaces of polarized human primary PTEC under inflammatory diseased conditions. PTEC were cultured under normal and inflammatory conditions on Transwell inserts to enable separate collection and isolation of apical/basolateral sEV. Significantly increased numbers of apical and basolateral sEV were secreted under inflammatory conditions compared with equivalent normal conditions. Multi‐omics analysis revealed distinct molecular profiles (lipids, microRNA, proteins) between inflammatory and normal conditions for both apical and basolateral sEV. Biological pathway analyses of significantly differentially expressed molecules associated apical inflammatory sEV with processes of cell survival and immunological disease, while basolateral inflammatory sEV were linked to pathways of immune cell trafficking and cell‐to‐cell signalling. In line with this mechanistic concept, functional assays demonstrated significantly increased production of chemokines (monocyte chemoattractant protein‐1, interleukin‐8) and immuno‐regulatory cytokine interleukin‐10 by peripheral blood mononuclear cells activated with basolateral sEV derived from inflammatory PTEC. We propose that the distinct molecular composition of sEV released from the apical versus basolateral membranes of human inflammatory PTEC may reflect specialized functional roles, with basolateral‐derived sEV pivotal in modulating tubulointerstitial inflammatory responses observed in many immune‐mediated kidney diseases. These findings provide a rationale to further evaluate these sEV‐mediated inflammatory pathways as targets for biomarker and therapeutic development.
Highlights
Kidney disease is a growing public health burden, affecting ∼10% of populations in industrialized countries (Gansevoort et al, 2013)
Human Proximal tubular epithelial cells (PTEC) were cultured to confluency on 0.4 μm Transwell inserts to generate an impermeable cell monolayer, enabling the characterisation of Small extracellular vesicles (sEV) produced from the apical plasma membrane into the upper compartment and basolateral plasma membrane into the lower compartment
The PTEC monolayer remained impermeable under both experimental conditions at this time-point, with the percent permeability measured at 0.75 ± 0.05% under normal conditions and 0.22 ± 0.05 under inflammatory conditions (Table 1)
Summary
Kidney disease is a growing public health burden, affecting ∼10% of populations in industrialized countries (Gansevoort et al, 2013). Irrespective of its origins, inflammation within the tubulointerstitial compartment, the interstitial tissue adjoining the renal tubules, is considered a central determinant in most forms of kidney injury (Andrade-Oliveira et al, 2019). In the initial injury phase, it has a protective function and is essential for tissue remodelling/repair (Rabb et al, 2016). If left unresolved, tubulointerstitial inflammation can drive a vicious cycle of uncontrolled tissue damage and functional decline, as observed in chronic kidney diseases (Cobo et al, 2018). Understanding the complex network of cell-to-cell communications between kidney tubular cells and inflammatory immune cells (e.g., monocytes, dendritic cells, T cells) is essential for developing clinical interventions to prevent this pathogenic transition to a chronic inflammatory state
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