Senescent vascular smooth muscle cells drive inflammation through an interleukin-1α-dependent senescence-associated secretory phenotype

Abstract

Objective-Vascular smooth muscle cells (VSMCs) that become senescent are both present within atherosclerotic plaques and thought to be important to the disease process. However, senescent VSMCs are generally considered to only contribute through inaction, with failure to proliferate resulting in VSMC-and collagen-poor unstable fibrous caps. Whether senescent VSMCs can actively contribute to atherogenic processes, such as inflammation, is unknown. Approach and Results-We find that senescent human VSMCs develop a proinflammatory state known as a senescenceassociated secretory phenotype. Senescent human VSMCs release high levels of multiple cytokines and chemokines driven by secreted interleukin-1α acting in an autocrine manner. Consequently, the VSMC senescence-associated secretory phenotype promotes chemotaxis of mononuclear cells in vitro and in vivo. In addition, senescent VSMCs release active matrix metalloproteinase-9, secrete less collagen, upregulate multiple inflammasome components, and prime adjacent endothelial cells and VSMCs to a proadhesive and proinflammatory state. Importantly, maintaining the senescence-associated secretory phenotype places a large metabolic burden on senescent VSMCs, such that they can be selectively killed by inhibiting glucose utilization. Conclusions-Senescent VSMCs may actively contribute toward the chronic inflammation associated with atherosclerosis through the interleukin-1α-driven senescence-associated secretory phenotype and the priming of adjacent cells to a proatherosclerotic state. These data also suggest that inhibition of this potentially important source of chronic inflammation in atherosclerosis requires blockade of interleukin-1α and not interleukin-1β.

IL‐1α cleavage by inflammatory caspases of the noncanonical inflammasome controls the senescence‐associated secretory phenotype

“…Here, we report increased CASP5 or Casp11 expression in senescent cells and a loss of cell surface and released IL‐1α without caspase‐5, leading to inhibition of the SASP. Interestingly, the SASP is not dependent on IL‐1β (Gardner et al, ; Orjalo et al, ), implying cleaved IL‐1α release occurs separately from IL‐1β (e.g., without caspase‐1/NLRP3/ASC), in contrast to other studies (Acosta et al, ). Indeed, IL‐1β release after icLPS requires caspase‐1 and caspase‐11, while IL‐1α only requires caspase‐11 (Figure g–j).…”

“…Although IL‐1α induces sterile inflammation upon release from damaged cells, it also drives the SASP, but in this context IL‐1α release or surface presentation occurs without cell death (Figure g and Gardner et al, ). This excludes the usual notion that IL‐1α is passively released (Kayagaki et al, ).…”

“…Knockdown in primary macrophages was performed with 10 pmol of nontargeting or CASP5 ‐targeting siGENOME siRNA pool (Dharmacon), while knockdown in IMR‐90 and WI‐38 cells was performed with 10 pmol of pooled or individual CASP5‐ or cGAS‐ targeting siGENOME siRNAs, using Lipofectamine RNAiMAX (Invitrogen) as per the manufacturer's instructions. Cell viability was assessed by LDH release (Pierce), or crystal violet staining as previously described (Gardner et al, ).…”

“…Thus, although cell cycle arrest during senescence limits cancer and the SASP instructs clearance of preneoplastic cells (Kang et al, ), this is balanced against establishment of a chronic inflammatory microenvironment that can damage tissue, drive disease and promote tumorigenesis if senescent cells persist (Grivennikov, Greten, & Karin, ). IL‐1α acts in an autocrine/paracrine fashion to drive the SASP (Gardner, Humphry, Bennett, & Clarke, ; Orjalo, Bhaumik, Gengler, Scott, & Campisi, ), with upstream expression controlled in part by ATM/ATR liberation of GATA4 from p62‐directed autophagy (Kang et al, ) and/or an mTORC1‐dependent pathway (Laberge et al, ). However, how IL‐1α is cleaved, activated or released during senescence to enable it to drive the SASP is unknown.…”

Diverse cellular architecture of atherosclerotic plaque derives from clonal expansion of a few medial SMCs

“…Unfortunately, mouse models of atherosclerosis are not well suited to address this question because cap SMCs do not undergo senescence in mice, possibly because of their extremely long telomeres (20). A trend toward increased patch size was seen with atherosclerosis progression, but the differences were nonsignificant (1-way ANOVA, log-transformed, P = 0.09).…”