Human Bronchial Fibroblasts (HBF)

BRPM_2.5 induces human bronchial fibroblasts differentiation into myofibroblasts and increases the expression of TRPC1.

Household air pollution (HAP) from biomass burning is a significant global health issue, contributing to severe respiratory diseases like COPD. PM_2.5, a primary pollutant from HAP, is linked to airway remodeling in COPD but its role in inducing fibrogenic myofibroblast transformation (FMT) remains unclear. Recent studies have found that transient receptor potential classical (TRPC) is involved in mediating cytoskeleton rearrangement of FMT. Therefore, Li et al. investigated whether PM_2.5-induced FMT is regulated by TRPC1 function or protein expression and explored the role of the PI3K/AKT signaling pathway in this process, providing insights into fibrosis pathogenesis and potential COPD therapy.

The sensitivity of HBF to BRPM_2.5 was assessed using the CCK8 assay, showing no effect on cell viability at concentrations below 30 ug/mL and exposure under 72 hours. However, BRPM_2.5 increased a-SMA and COL I expression in a time-dependent manner and caused morphological changes similar to TGF-β1, leading to the differentiation of HBF into contractile myofibroblasts and significant collagen contraction (Fig. 1). These findings suggest BRPM_2.5 induces FMT. Then, they examined BRPM_2.5's impact on TRPC expression. GPCR analysis showed TRPC1 mRNA levels were higher in HBF than TRPC3, TRPC4, TRPC5, TRPC6, and TRPCZ. HBF exposed to BRPM_2.5 increased TRPC1 and TRPC3 mRNA expression but not TRPC4 and TRPC6 (Fig. 2a). They thus focused on TRPC1's role in BRPM_2.5-induced FMT. BRPM_2.5 treatment elevated TRPC1 mRNA after 12, 24, and 48 hours (Fig. 2b). Western Blot confirmed TRPC1 protein levels rose significantly after 24, 48, and 72 hours of BRPM_2.5 exposure (Fig. 2c). Cellular immunofluorescence showed increased TRPC1 protein in HBF after 24 hours of BRPM_2.5 stimulation, localized in both the cytoplasm and nucleus (Fig. 2d). These results suggest TRPC1 is involved in BRPM_2.5's effects on FMT.

Fig. 2. The effect of BRPM_2.5 on fibroblasts (Li, S., Qu, L., et al., 2024).

Fig. 2. The effect of BRPM_2.5 on TRPC expression in fibroblast-myofibroblast transition (Li, S., Qu, L., et al., 2024).

IL6 and IL8 Secretion from HBF Treated with Eosinophil-Derived Supernatants Is Dependent on the IL1 Receptor

Eosinophils contribute to allergic inflammation in asthma in part via elaboration of a complex milieu of soluble mediators. Human bronchial fibroblasts (HBF) respond to stimulation by these mediators by acquiring a pro-inflammatory profile including induction of interleukin 6 (IL6) and IL8. Bernau et al. aimed to identifie key eosinophil-derived factors that mediate IL6 and IL8 induction in human bronchial fibroblasts (HBF).

The prior transcriptomic analysis indicated that IL1 signaling might mediate fibroblast responses to eosinophil-derived mediators. To test this, they used IL1RA, an IL1R inhibitor. Treatment with eosinophil supernatants significantly increased IL8 and IL6 secretion by airway fibroblasts, confirmed by ELISA (Fig. 3A and B). Pre-treating HBF with IL1RA reduced IL8 and IL6 protein release, suggesting dependency on IL1 signaling (Fig. 3A and B). They then examined the effect of IL1RA inhibition on HBF-induced CXCL8 and IL6 transcription by eosinophil-derived products. They found that IL1RA reduced the transcription of CXCL8 and IL6 in response to eosinophil-derived products (Fig. 3C and D), indicating the essential role of IL1R in gene upregulation.

Fig. 3. Interleukin 6 (IL6) and IL8 expression and secretion by human bronchial fibroblasts stimulated with eosinophil-derived soluble mediators requires signaling via the IL1 receptor (Bernau, K., Leet, J. P., et al., 2021).