Cellular senescence and EMT crosstalk in bleomycin‐induced pathogenesis of pulmonary fibrosis—an in vitro analysis

Abstract

With poor prognosis and aberrant lung remodeling, pulmonary fibrosis exhibits worldwide prevalence accompanied by an increase in burden in terms of hospitalization and death. Apart from genetic and non‐genetic factors, fibrosis occurs as a side effect of bleomycin antineoplastic activity. Elucidating the cellular and molecular mechanism could help in the development of effective anti‐fibrotic treatment strategies. In the present study, we investigated the underlying mechanism behind bleomycin‐induced fibrosis using human alveolar epithelial cells (A549 cells). On the basis of the experimental observation, it was demonstrated that with transforming growth factor‐β (TGF‐β) as a central mediator of fibrosis progression, a cross‐talk between epithelial–mesenchymal transition (EMT) and senescence upon bleomycin treatment occurs. This results in the advancement of this serious fibrotic condition. Fibrosis was initiated through integrin activation and imbalance in the redox state (NOX expression) of the cell. It progressed along the TGF‐β‐mediated non‐canonical pathway (via ERK phosphorylation) followed by the upregulation of α‐smooth muscle actin and collagen synthesis. Additionally, in this process, the loss of the epithelial marker E‐cadherin was observed. Furthermore, the expressions of senescence markers, such as p21 and p53, were upregulated upon bleomycin treatment, thereby intensifying the fibrotic condition. Accordingly, the molecular pathway mediating the bleomycin‐induced fibrosis was explored in the current study.

Endothelin-1 induces cellular senescence and fibrosis in cultured myoblasts. A potential mechanism of aging-related sarcopenia

“…This result suggests that FN can be mediating the effect of ET-1 on myoblast senescence through integrin activation, by an unknown mechanism which needs more studies. According with us, some authors suggested that the integrin signaling can contribute not only to senescence but also fibrosis effects, for instance, cellular senescence caused by deficiency of retinoic acid inducible gene-I (Rig-I) through amplifying integrin ß3/p38 MAPK signaling [42]; and bleomycin-induced fibrosis initiated through integrin activation and imbalance in the redox state of the cell [43].…”

“…Likewise, when ILK was silenced in C2C12, FN did not increase p16 expression, suggesting that ILK activation might be implied in the senescence induced by FN. Briefly, the mechanism could involve the integrin/ILK activation through extracellular FN which could activate some downstream signaling pathway such as p38/ErK/MAPK or even PI3K-AKT-GSKβ [42][43][44][45], causing senescence. However, further studies to evaluate the underlying mechanism behind FN-induced senescence are needed.…”

Senescence of alveolar epithelial cells impacts initiation and chronic phases of murine fibrosing interstitial lung disease

“…Previous studies reported the senescence of fibroblasts, AEC, and/or endothelial cells in human IPF (22-28) as well as in murine BLM-ILD (29)(30)(31)(32)(33). However, which senescent cells exhibit the SASP-mediated production of inflammatory mediators and contribute to the development of lung fibrosis has not been clarified.…”

“…Previous studies have shown that in human IPF, DNA damage and expressions of SA-βgal, p16 INK4A , p53, or p21 WAF1/CIP1 have been observed in lung fibroblasts and/or epithelial cells ( 22 – 28 ). Similar to human IPF, senescence markers or SASP have been detected in AEC and/or fibroblasts in bleomycin-induced ILD (BLM-ILD) ( 29 – 33 ). Since BLM elicits DNA damage in cell lines and primary cells, including epithelial cells and fibroblasts ( 34 ), its intratracheal instillation is considered to induce DNA damage and resultant senescence in the lung cells of BLM-ILD.…”

Regeneration or Repair? The Role of Alveolar Epithelial Cells in the Pathogenesis of Idiopathic Pulmonary Fibrosis (IPF)

“…Recently, Moimas et al reported that ATII cells purified from IPF patients exhibit high levels of the p21 and p16 senescence markers, as well as the ZEB-1 and ZEB-2 EMT markers, demonstrating that these two events cross react with each other [25]. Another work published by Muthuramalingam [34] revealed that the A549 human cell line treated with bleomycin in vitro expressed high levels of senescence and EMT markers, favoring a pro-fibrotic microenvironment that could lead to secretion of TGF-β, identified as the central mediator that links EMT and senescence [34]. Moreover, Faheem et al showed that in carcinogenesis, senescent cells secrete high levels of senescence-associated secretory phenotype (SASP) factors and TGF-β, promoting the activation of the EMT process and, later, leading to the myofibroblastic differentiation and production of ECM components [35].…”