Effects of vascular leakage on the phenotype and function of airway smooth muscle cells in asthma

Abstract

Vascular leakage is a prominent feature of asthma. During this process many biologically active plasma proteins escape from the blood vessels into the surrounding airway tissues and induce alterations in the tissues and their cells. The effects of serum on the phenotype and function of dog airway smooth muscle (ASM) cells have been examined in detail (Ma, Wang et al. 1998; Halayko, Camoretti-Mercado et al. 1999). The findings of these studies demonstrate clearly that the presence or absence of serum for prolonged periods induces alterations in the phenotype and function of dog ASM cells in culture. Specifically, in the presence of serum, freshly isolated dog ASM cells modulate from a contractile to a proliferative/synthetic phenotype (Halayko, Salari et al. 1996). In contrast, when confluent ASM cells are serum deprived for a long time in culture, hyper-contractile ASM cells start to appear (Ma, Cheng et al. 2002). This process of phenotypic modulation has been hypothesised to occur in asthma particularly during periods of microvascular leakage (MVL) (Hirst 1996). The aim of this thesis was to examine the effects of serum and its prolonged withdrawal on the phenotype (chapter 2) and function (chapter 3) of human ASM cells with particular emphasis on cells from asthmatic donors. The phenotype of ASM cells was assessed by size, complexity and their expression of the adhesion molecule CD44, a proposed marker for proliferation, and proteins associated with contraction: muscarinic receptor sub-type 3 (M3R), sm-actin, hcalponin and smooth muscle myosin heavy chain (sm-MHC) using flow cytometry. In asthmatic ASM cells these phenotypic markers were the same before and after serum starvation. However, in non-asthmatic ASM cells after prolonged serum starvation, only significant decreases in the expression of CD44 and sm-actin and a significant increaseunderstanding o f the effects of serum on the phenotype and function of asthmatic and non-asthmatic ASM cells, and thus the possible effects of MVL on ASM in asthma.