Inflammatory cytokines promote growth of intestinal smooth muscle cells by induced expression of PDGF‐Rβ

Abstract

Thickening of the inflamed intestinal wall involves growth of smooth muscle cells (SMC), which contributes to stricture formation. Earlier, the growth factor platelet-derived growth factor (PDGF)-BB was identified as a key mitogen for SMC from the rat colon (CSMC), and CSMC growth in colitis was associated with both appearance of its receptor, PDGF-Rβ and modulation of phenotype. Here, we examined the role of inflammatory cytokines in inducing and modulating the growth response to PDGF-BB. CSMC were enzymatically isolated from Sprague–Dawley rats, and the effect of tumour necrosis factor (TNF)-α, interleukin (IL)-1β, transforming growth factor (TGF), IL-17A and IL-2 on CSMC growth and responsiveness to PDGF-BB were assessed using proliferation assays, PCR and western blotting. Conditioned medium (CM) was obtained at 48 hrs of trinitrobenzene sulphonic acid-induced colitis. Neither CM alone nor cytokines caused proliferation of early-passage CSMC. However, CM from inflamed, but not control colon significantly promoted the effect of PDGF-BB. IL-1β, TNF-α and IL-17A, but not other cytokines, increased the effect of PDGF-BB because of up-regulation of mRNA and protein for PDGF-Rβ without change in receptor phosphorylation. PDGF-BB was identified in adult rat serum (RS) and RS-induced CSMC proliferation was inhibited by imatinib, suggesting that blood-derived PDGF-BB is a local mitogen in vivo. In freshly isolated CSMC, CM from the inflamed colon as well as IL-1β and TNF-α induced the early expression of PDGF-Rβ, while imatinib blocked subsequent RS-induced cell proliferation. Thus, pro-inflammatory cytokines both initiate and maintain a growth response in CSMC via PDGF-Rβ and serum-derived PDGF-BB, and control of PDGF-Rβ expression may be beneficial in chronic intestinal inflammation.

Intestinal smooth muscle phenotype determines enteric neuronal survival via GDNF expression

“…To test this and to ensure relevance in vivo, smooth muscle cells were isolated from the circular smooth muscle layer of the adult rat colon (CSMC) as described earlier (Nair et al, 2014), and examined for GDNF expression. Typically, the freshly isolated CSMC rounded up and adhered to the culture substrate within hours of plating, with progressive attachment and spreading by 4 days and development of near-confluent cultures by 8 days in vitro (Fig.…”

“…Adult circular smooth muscle culture: The isolation and enzymatic dissociation of circular smooth muscle from the rat colon was based on a previously published protocol (Nair et al, 2014). For this, the mid-descending colon of adult male rats was isolated and the intestinal mucosa, serosa and longitudinal intestinal smooth muscle layer were separated from the circular smooth muscle layer with fine forceps.…”

“…The major factor influencing the onset of proliferation by ISMC is acquisition of sensitivity to the known smooth muscle mitogen PDGF-BB, via the onset of expression of its receptor, PDGF-Rb (Stanzel et al, 2010;Nair et al, 2014). This receptor is normally not expressed in these cells, but appears among control cells shortly after enzymatic isolation and tissue culture, as well as by 24 h after intracolonic TNBS administration in the rat.…”

Global Hypoxia-Ischemia Induced Inflammation and Structural Changes in the Preterm Ovine Gut Which Were Not Ameliorated by Mesenchymal Stem Cell Treatment

“…The inflammation-induced thickening of the circular and longitudinal muscle layers could be explained by several mechanisms, including hypertrophy and/or secretion of inflammatory cytokines, which are considered to have mitogenic effects on muscle cells (46,50,62). In line with these reports, muscle thickening after HI in our animal model was accompanied by increased cell numbers and cell proliferation within the muscle layers of the fetal intestine and elevated mRNA levels of IL-1b and IL-17, two proinflammatory cytokines that are known to promote intestinal muscle growth (50). Therefore, we speculate that the inflammatory cytokines IL-1b and IL-17 may contribute to the muscle hyperplasia detected 7 d after UCO.…”

“…Importantly, the significant increase of CD3 + cells in the circular muscle of the HI + MSC group was maintained, even in the absence of the highest value within this HI + MSC group ( Figure 3D). We further characterize the intestinal inflammatory response by measuring mRNA levels of interleukin (IL)-1b and IL-17, two proinflammatory cytokines with mitogenic capacities that are upregulated following HI (12,50). Fetal HI, with or without MSC treatment, increased the intestinal mRNA levels of IL-1b compared with control ( Figure 4A).…”