Ablation of interleukin-4 receptor alpha in macrophages ameliorates fibrotic NASH phenotype in murine nonalcoholic steatohepatitis

The role of immune cell populations in NASH-related inflammation and fibrosis remains controversial. However, targeting of specific receptors that switch immune cell phenotypes is attractive. We aimed to study the role IL-4 receptor alpha (IL-4Rα) which represents a central switch to generate Th2 T cells and M2 macrophages upon stimulation with interleukin (IL)-4 and IL-13 in a representative mouse model of NASH.

Methods and Results:

8-week-old male Balb/C wild type mice and Balb/C mice with general or macrophage specific deletion of IL-4Rα (Balb/C IL-4R^-/^- and LysM^creIL-4Rα^-/^lox mice) were fed a choline-deficient, l-amino acid-defined (CDAA) and choline supplemented diet (CSAA) diet for an additional 12 weeks. There was significant decrease in the liver weights of both the KO strains compare to the wild type mice in CDAA fed mice. H&E stained sections revealed a significant reduction of the NAS score (adapted for mice) and extent of fibrosis in Balb/C IL-4Rα^-/^- B and Balb/C LysM^creIL-4Rα^-/^lox mice compared to the wild type controls. Hydroxyproline assay revealed significant reduction of fibrosis in CDAA fed IL-4Rα KOs mice compare to the CDAA fed wild type control. In wild type mice, steatosis was > 66% and macrovesicular, whereas steatosis in the IL-4Rα knockout mice was reduced and more concentrated in zone 3 with more microvesicular fat. Fibrosis score was 2. X in the wildtype vs. < 1 in both knockout strains. Moreover, Sirius Red morphometry and alpha SMA immunohistochemistry staining revealed significant reduction of fibrosis in the Balb/C IL-4Rα^-/^- and Balb/C LysM^creIL-4Rα^-/^lox mice compare to wild type mice fed CDAA diet. Specifically, CD68⁺ macrophages, ki67⁺ cells were significantly decreased in both L-4Rα KOs compared to the wildtype mice. This was paralleled by significantly suppressed hepatic transcript levels for Col1a1, Tgfb and Tnfa. Population of CD11b⁺F4/80^-Ly6G^-Ly6c^high were significantly reduced in KOs fed CDAA compare to WT mice fed CDAA diet.

Conclusion:

1. ablation of the IL-4Rα alpha on macrophages as well as in general, comparably suppressed steatosis, inflammation and fibrosis in the CDAA model of NASH; 2. IL-4Rα targeted therapies, including inhibition of IL-4 and IL-13 is a potential therapy of fibrotic NASH.