Mitogenic factors promoting intestinal smooth muscle cell proliferation

Area of Science:

• Gastroenterology
• Cell Biology
• Molecular Biology

Background:

• Intestinal smooth muscle cells (CSMC) in the colon are normally quiescent.
• Trinitrobenzene sulfonic acid (TNBS)-induced colitis in rats causes CSMC proliferation, increased cell number, and altered phenotype.
• The specific factors driving CSMC proliferation during colitis remain unclear.

Purpose of the Study:

• To investigate the factors that stimulate proliferation of rat colonic CSMC.
• To determine the role of platelet-derived growth factor receptor-beta (PDGF-Rβ) in CSMC proliferation during inflammation.

Main Methods:

• Primary cultures of rat colonic CSMC were treated with various growth factors (PDGF-AA, PDGF-BB, FGF, EGF, IGF-1).
• Cell proliferation was assessed by [3H]thymidine incorporation and bromodeoxyuridine uptake.
• PDGF-Rβ expression, phosphorylation, and downstream signaling pathways (Akt, ERK) were analyzed using qPCR, Western blot, and immunocytochemistry.
• CSMC were isolated from control and TNBS-colitis rats to assess PDGF-Rβ expression and signaling in vivo.

Main Results:

• PDGF-BB and IGF-1 significantly increased CSMC proliferation, with PDGF-BB being more potent.
• CSMC initially lacked PDGF-Rβ expression but gained it in vitro, responding to PDGF-BB but not IGF-1.
• PDGF-BB induced PDGF-Rβ phosphorylation and activated Akt and ERK pathways, crucial for proliferation.
• In vivo, PDGF-Rβ expression and phosphorylation were rapidly induced in CSMC during TNBS-colitis, correlating with maximal proliferation.

Conclusions:

• The onset of PDGF-Rβ expression is a critical factor for CSMC proliferation in vitro and in vivo.
• Inflammation during colitis may disrupt inhibitory mechanisms, leading to CSMC hyperplasia.
• PDGF-BB signaling through PDGF-Rβ is a key driver of CSMC growth in inflammatory conditions like colitis.