In Vitro Smooth Muscle Hypercontractility Induced by Cd4+ T Cells is Transient

Abstract

Smooth muscle (SM) hypercontractility is a characteristic of several pathologies, including asthma. Inflammatory cells and/or the cytokines they release may alter contractile protein expression, thereby also altering the SM mechanics. We characterized the maximal unloaded shortening velocity (Vmax), stress (force/cross sectional area), and contractile protein expression of Brown Norway rat airway SM co-cultured with activated CD4+ T cells for 24h and 48h. After 24h incubation, Vmax (mean±SEM) was significantly increased (0.15±0.01 l/s vs. 0.29±0.02 l/s; control vs. T cells, p = 0.0012). However, this alteration in Vmax was transient and disappeared after 48h of co-incubation (0.21±0.01 vs. 0.25±0.01 l/s, p = 0.099). No significant differences in stress were observed at 24h or 48h. Western blot analysis showed a significant increase in the levels of MLCK (0.20±0.03 vs. 0.41± 0.09; control vs. T cells; p<0.05, p=0.018) and the (+)insert SM myosin isoform (0.55±0.04 vs. 0.81±0.05; p = 0.0023) after 24h incubation with the CD4+ T cells. These alterations were also transient; all values returned to baseline after 48h exposure to the CD4+ T cells. Thus, the increase in Vmax was correlated with the increase in MLCK and (+)insert isoform expression. Conversely, there were no differences in levels of total SM myosin heavy chain or α-smooth muscle actin, suggesting there was no increase in muscle mass. These results show that indeed inflammatory cells and/or their mediators can alter SM contractile protein expression and SM function, but that these effects may be transient. This transient behavior may be important to consider when studying SM function in disease.Supported by: CIHR, NIH-RO1HL103405.