Interleukin-34 Stimulates Gut Fibroblasts to Produce Collagen Synthesis

Abstract

Background and Aim The mechanisms underlying the formation of intestinal fibrostrictures [FS] in Crohn’s disease [CD] are not fully understood, but activation of fibroblasts and excessive collagen deposition are supposed to contribute to the development of FS. Here we investigated whether interleukin-34 [IL-34], a cytokine that is over-produced in CD, regulates collagen production by gut fibroblasts Methods IL-34 and its receptor macrophage colony-stimulating factor receptor 1 [M-CSFR-1] were evaluated in inflammatory [I], FS CD, and control [CTR] ileal mucosal samples by real-time polymerase chain reaction [RT-PCR], western blotting, and immunohistochemistry. IL-34 and M-CSFR-1 expression was evaluated in normal and FS CD fibroblasts. Control fibroblasts were stimulated with IL-34 in the presence or absence of a MAP kinase p38 inhibitor, and FS CD fibroblasts were cultured with a specific IL-34 antisense oligonucleotide, and collagen production was evaluated by RT-PCR, western blotting, and Sircol assay. The effect of IL-34 on the wound healing capacity of fibroblasts was evaluated by scratch test. Results We showed enhanced M-CSFR-1 and IL-34 RNA and protein expression in FS CD mucosal samples as compared with ICD and CTR samples. Immunohistochemical analysis showed that stromal cells were positive for M-CSFR-1 and IL-34. Enhanced M-CSFR-1 and IL-34 RNA and protein expression was seen in FS CD fibroblasts as compared with CTR. Stimulation of control fibroblasts with IL-34 enhanced COL1A1 and COL3A1 expression and secretion of collagen through a p38 MAP kinase-dependent mechanism, and wound healing. IL-34 knockdown in FS CD fibroblasts was associated with reduced collagen production and wound repair. Conclusions Data indicate a prominent role of IL-34 in the control of intestinal fibrogenesis.

The twin cytokines interleukin-34 and CSF-1: masterful conductors of macrophage homeostasis

“…This increase in IL-34 induced macrophage differentiation and the expression of pro-inflammatory factors TNF-α and IL-6 119 . Franzè et al 122 recently demonstrated that IL-34, through specific activation of the p38 MAP pathway, induced the secretion of collagen and contributed to wound healing in CD patients.…”

Mechanism of fibrosis and stricture formation in Crohn's disease

“…44 Beyond the classical cytokines, ileal mucosa has upregulation of IL-34 and its receptor M-CSFR-1. 45 TGF-β, one of the main pro-fibrotic factors that also has immunoregulatory properties, shows upregulation in the mucosa, 38 submucosa and muscle 42,43 ( Figure 4B). Based on histopathological studies, TGF-β shows widespread staining in stricture sections (in all wall layers), and TGF-β co-localizes with aggregates of mononuclear or lymphoid cells.…”

“…IL‐17 may have a role in stricture development, and a recent review summarized the potential for Th17/IL‐17 involvement in intestinal fibrosis 44 . Beyond the classical cytokines, ileal mucosa has upregulation of IL‐34 and its receptor M‐CSFR‐1 45 …”

“…Knocking down IL-34 in fibroblasts isolated | 11 of 23 ALFREDSSON AND WICK from these specimens reduced collagen production. 45 Thus, several cytokines in the stricture microenvironment influence fibroblast behaviour including collagen production.…”

Intestinal stricture in Crohn's disease: A 2020 update

“…There is abundant indirect evidence that profibrotic cytokines, including interleukin (IL), TGF‐β1, platelet‐derived growth factor (PDGF) generated by immune or non‐immune cells, play a vital role in the process of intestinal fibrosis 5 . In 2020, Franzè et al 20 have demonstrated that IL‐34 can enhance the production of collagen in fibroblasts through p38 mitogen‐activated protein kinase (MAPK)‐dependent pathway. In addition to cytokines, factors involved in cellular oxidative stress, such as hyperactive nicotinamide adenine dinucleotide phosphate, also known as oxidase 4 (NOX4), has been found to have an impact on fibrosis of the intestine as well 21 .…”