Role of IL-4, IL-13, and STAT6 in inflammation-induced hypercontractility of murine smooth muscle cells
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T helper 2 (Th2) cytokines interleukin (IL)-4 and IL-13, which activate signal transducer and activator of transcription 6 (STAT6) are expressed in the muscularis externa during nematode infection and are candidate mediators of the associated hypercontractility. To determine the locus of action of these cytokines, we examined the IL-4- and IL-13-induced hypercontractility of the isolated muscle cells from STAT6 +/+ and STAT6 -/- mice. We compared the results with cells isolated from Trichinella spiralis-infected STAT6 +/+ and STAT6 -/- mice. Carbamylcholine chloride (Carbachol) induced the contraction of jejunal muscle cells in a concentration-dependent manner maximal contraction (R(max) 26.7 +/- 1.9%). Cells from T. spiralis-infected STAT6 -/- mice showed the hypertrophy (cell lengths 41.4 +/- 0.8 to 89.0 +/- 8.7 microm) and hypercontractility (R(max) 37.5 +/- 1.3%) induced by infection. IL-4Ralpha mRNA was detected in dispersed smooth muscle cells. Incubation of longitudinal muscle-myenteric plexus (LMMP) with IL-4 and IL-13 enhanced Carbachol-induced muscle contraction (R(max) 35.5 +/- 1.9 and 32.4 +/- 2.9%, respectively). Incubation of LMMP from STAT6 -/- mice with IL-4 did not enhance the contraction. The hypercontractility in T. spiralis-infected mice was attenuated in STAT6 -/- mice (P < 0.02). These results indicate both IL-4 and IL-13 induce hypercontractility of muscle cells via the STAT6 pathway, and this is the basis for hypercontractility observed in T. spiralis-infected mice.
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