IL-1 beta and IL-6 induce hyperplasia and hypertrophy of cultured guinea pig airway smooth muscle cells

Abstract

Guinea pig airway smooth muscle (ASM) cells were maintained in a primary tissue culture (passages 1-3). Cells were exposed to human recombinant interleukin-1 beta (IL-1 beta; 20-100 pg/ml) or interleukin-6 (IL-6; 1-4 ng/ml) in the presence of indomethacin (1 microgram/ml) for up to 5 days. Proliferation of ASM cells was assessed with two techniques, direct counting of cells with a hemacytometer and [3H]thymidine incorporation corrected for total protein content. Hypertrophy of ASM cells was assessed by [3H]leucine incorporation (evaluation of protein synthesis), determination of total DNA content, DNA content per cell, and protein content per cell. We observed that the exposure of ASM cells to human recombinant IL-1 beta or IL-6, in all studied concentrations, significantly increased the number of cells as well as [3H]thymidine incorporation into ASM cells. We also found that exposure of ASM to these two cytokines increased [3H]leucine incorporation into the ASM cells and increased protein content and DNA content per single cell. These changes were also concentration dependent. We conclude that the two proinflammatory cytokines, IL-1 beta and IL-6, which are present in asthmatic lungs, increased the proliferation of ASM cells (hyperplasia) as well as their overall size and size of their nuclei, as measured by biochemical markers. These findings are compatible with the presence of ASM hypertrophy.

Airway pathology in asthma: Fig. 1.—

“…The increase in smooth muscle mass may be due to several factors, including proliferation of smooth muscle induced by inflammatory mediators [26], cytokines [27] and growth factors [28,29]. It has been suggested that an intrinsic abnormality of smooth muscle may underlie asthma severity, but data are lacking to support this hypothesis.…”

Phenotypic diversity and molecular mechanisms of airway smooth muscle proliferation in asthma

“…Broadly, the substances now implicated in mitogenesis of airway smooth muscle, in addition to the action of serum itself (discussed in [49]), include pro-inflammatory mediators (histamine [46], 5-hydroxytryptamine (5-HT) [50], phenylephrine [51], tachykinins [52], endothelin (ET)-1 [53±56] and leukotriene D 4 [57]), several inflammatory cell-and plasma-derived enzymes (a-thrombin [58], tryptase [59], b-hexosaminidase and b-glucuronidase [60]), polypeptide growth factors (platelet-derived growth factor (PDGF) [61], epidermal growth factor (EGF) [62], fibroblast growth factor-2 (FGF-2) [63] and insulin-like growth factors (IGFs) [64]) and thromboxanes [65]. Pro-inflammatory cytokines (interleukin-1b [66], interleukin-6 [67], and tumour necrosis factor-a [68]) also induce a proliferative response in airway smooth muscle, which is revealed only under conditions of cyclo-oxygenase inhibition [69], in which the production and action of inhibitory prostanoids such as prostaglandin E 2 is limited. Other trophic factors such as altered mechanical stress [70] and reactive oxygen species [71] have also been identified.…”

Nucleotides induce IL-6 release from human airway epithelia via P2Y2and p38 MAPK-dependent pathways

“…Interleukin-6 (IL-6) is a pleiotropic cytokine that is generally considered proinflammatory. It exerts numerous functions, including the induction of pulmonary neutrophil infiltration, airway mucus secretion, lung fibrosis, and hyperplasia and hypertrophy of airway smooth muscle cells (16,19,28,42). Increased production of IL-6 has been observed in the airways of patients with asthma, COPD, ARDS, and VILI (5,11,40,44,54).…”