Senescence Associated Secretory Phenotype Regulation in Lung Aging and Malignancy Progression
Cellular senescence is a unique cell fate characterized by stable cell cycle arrest and the extensive production and secretion of various cytokines, chemokines, proteases, and growth factors, a phenomenon known as the senescence-associated secretory phenotype (SASP). Although secreted factors are known to have important biological effects on both senescent and non-senescent cells in the contexts of normal aging and disease, the precise molecular mechanisms responsible for generating a SASP in response to senescent stimuli have remained largely obscure. To identify the major initiator, we used an unbiased profiling strategy and discovered a multi-ligand scavenger receptor CD36 is rapidly upregulated in multiple cell types in response to replicative, oncogenic and chemical senescent stimuli. Moreover, ectopic CD36 expression in dividing mammalian cells is sufficient to initiate the production of a large subset of known components of the SASP via activation of the canonical Src-NFκB pathway, resulting in the subsequent onset of a full senescent state. The CD36-mediated secretome is further shown to be ligand-dependent, as fibroblast cultures lacking the CD36 ligand amyloid beta (Aβ) are unresponsive to CD36 upregulation but can be driven to senesce by the addition of exogenous ligand. Finally, loss-of-function experiments revealed a strict requirement for CD36 in secretory molecule production during conventional senescence reprogramming. These results uncover the Aβ-CD36-NFκB signaling axis as an important regulator of the senescent cell fate via induction of the SASP.
To further explore the possible implication of Aβ-CD36-NFκB-SASP signaling, we found that the CD36 expression is significantly down-regulated in the context of lung malignant tissues, specifically in cancer cells. Subsequent explorations revealed CD36 as a strong tumor suppressor by secreting pro-inflammatory cytokines and recruiting cytotoxic T. For the CD36 ligand - Aβ, we observed a major accumulation in the tumor region which might serve as the tumor-suppressing signaling initiation cue once CD36 is introduced. The findings indicate a possible tumor suppressive signaling lead by Aβ-CD36.
Taken together, we discovered a novel signaling of Aβ-CD36-NFκB in regulating SASP during the process of lung aging and the progression of lung malignancy.
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