CC16-TNF-α negative feedback loop formed between Clara cells and normal airway epithelial cells protects against diesel exhaust particles exposure-induced inflammation

Abstract

CC16 is almost exclusively expressed in non-ciliated epithelial Clara cells, and widely used as a Clara cell marker. Diesel exhaust particles (DEPs), the fine particulate matters produced by diesel engines, cause or exacerbate airway-related diseases. Our previous study documented that DEP inhibits the CC16 expression in the immortalized mouse Clara cell line through methylation of C/EBPα promoter. However, the molecular mechanism by which DEP regulates CC16 secretion is unclear. Here, we isolated CC16 containing Clara cells (CC16 + ) from human distal lung, and found that DEP inhibited CC16 secretion from CC16 + cells via methylation of C/EBPα and inhibition of Munc18b transcription. CC16 + cell conditioned media containing different concentrations of CC16 was prepared and used for culture of airway epithelial cells BEAS-2B with no expression of CC16. A positive correlation was observed between CC16 level and DEP-induced autophagy activity, and a negative correlation between CC16 level and DEP-induced pro-inflammatory cytokine TNF-α, IL-6, and IL-8 level, suggesting that CC16 might mitigate DEP-induced inflammation via promoting autophagy in BEAS-2B cells. This result was further confirmed by adding recombinant CC16 to BEAS-2B cells exposed to DEP. Moreover, CC16 level was significantly increased when CC16 + cells were cultured in BEAS-2B cell conditioned medium containing TNF-α or the normal medium supplemented with recombinant TNF-α, suggesting that TNF-α induced CC16 production and secretion from CC16 + cells. Collectively, these data point that CC16 and TNF-α form a negative feedback loop, and this negative feedback loop between Clara cells and normal airway epithelial cells protects against DEP exposure-induced inflammation.

Club Cells—A Guardian against Occupational Hazards

“…On one side, TNF induced CCSP secretion in club cells [74]. This effect was also noticed after exposure of club cells to diesel exhaust, as a useful restoration of CCSP secretion after the DEP-generated methylation of C/EBPα promoter of SCGB1A1 [75].…”

Role of club cell 16‐kDa secretory protein in asthmatic airways

“…The current study showed that CC16 could reduce the release of non‐type 2 inflammatory cytokines (IL‐8 and MMP‐9) from AECs in response to HDM. Previous studies reported that CC16 could reduce tumour necrosis factor [TNF]‐α, IL‐1β, IL‐8 and MMP‐9 in response to LPS and diesel exhaust particles through inhibiting the expression of NF‐κB pathway 33–35 . Meanwhile, the overproduction of oxidative stress from AECs upon environmental stimuli/irritant exposure‐induced non‐type 2 inflammation through the production of IL‐8, IL‐1β and TNF‐α 7,36,37 .…”

Inactivation of the TGF-β1/ALK5 axis enhances club cell function and alleviates lung tissue damage to ameliorate COPD progression through the MEK/ERK signaling pathway

“…Club cell secretory protein (CCSP), also known as club cell protein 16 (CC16) or CC10, is a 15.8 kDa protein primarily released in the terminal bronchioles, where club cells are located (Almuntashiri et al 2020). CC16 plays a signi cant protective role in reducing oxidative stress and in ammation in the respiratory tract, while also serving as a peripheral lung marker to assess the integrity and permeability of lung epithelial cells (Hu et al 2021). More speci cally, CC16 has the potential to be a therapeutic target for COPD (Martinu et al 2023).…”