Airway smooth muscle contractility is increased following coculture with fibrocytes

Abstract

Airway smooth muscle (ASM) in asthma is hypercontractile. Fibrocytes are elevated in peripheral blood and ASM in asthma and ASM has the potential to mediate fibrocyte recruitment. We hypothesised that fibrocytes contribute to ASM hypercontractility in asthma.

Contraction was assessed using the collagen gel contraction assay. Fibrocytes were labelled with the fluorescent marker CFSE enabling the number of fibrocytes per 1.25x10⁵ ASM cells to be calculated. Area under the curve of gel size as a percentage of well area over a 180 min period (AUC₁₈₀) was calculated.

A significant increase was seen in contraction (i.e. reduction in AUC₁₈₀) of collagen gels impregnated with ASM cells (1.25x10⁵) cocultured with fibrocytes for 3-4 days versus ASM alone. This was inhibited when fibrocyte-ASM adhesion was prevented using a transwell. ASM contraction was not affected by fibrocyte-ASM coculture conditioned media nor by fibrocytes when added with ASM to collagen gels with no prior coculture – 0 days (ratios ranging from 1 fibrocyte: 4-32 ASM cells), see table 1. The increase in contraction seen following coculture (AUC₁₈₀ ASM-coculture) correlated with the number of fibrocytes present per 1.25x10⁵ ASM (r=0.68, p=0.002).

Fibrocyte-ASM coculture promotes ASM hypercontractility, which is partly cell-cell adhesion-dependent.