Innate Immunity Receptor TLR9 Drives Erythrocyte Cholesterol and Ferroprotin Accumulation in a Glutaminase-Independent Manner. Implications for Metabolic Associated Fatty Liver Disease.

Abstract

Background: During metabolic associated fatty liver disease (MAFLD), lipotoxicity induces toll-like receptor 9 (TLR9) upregulation and mitochondrial DNA-induced TLR9 activation in the liver, driving metabolic hepatic inflammation. We wondered whether there is augmented erythrocyte TLR9 in MAFLD and we explored the effect of erythrocyte TLR9 activation on cholesterol and sphingomyelin content, glutaminase activity and TLR9, ferroportin and monocyte chemoattractant protein 1 (MCP-1) levels.

Methods: Twenty-four patients (15 men and nine women) with MAFLD and nine healthy controls (four men and five women) were enrolled. Erythrocytes were isolated from EDTA-containing blood. Protein levels were measured in erythrocyte lysates (Triton X-100 0.1% v/v), erythrocyte membranes (isolated by hypotonic lysis) with enzyme-linked immunosorbent assays, whereas lipids and enzyme activities were measured in erythrocyte hemoglobin-free membranes by a semi-quantitative thin layer chromatography and assay kits, respectively.

Results: The total but not surface levels of TLR9 were increased (p=0.002) in erythrocytes of MAFLD patients. Erythrocyte TLR9 activation drove cholesterol and ferroportin-1 accumulation, but not glutaminase-1 upregulation. Toll-like receptor 9 activation did not induce a significant change on the levels of TLR9 and MCP-1.

Conclusions: Erythrocyte TLR9 is upregulated in MAFLD patients and drives cholesterol and ferroportin-1 accumulation in a glutaminase-independent manner. Augmented erythrocyte TLR9 could participate in metabolic inflammation during MAFLD.