Oxysterols Modulate Protein–Sterol Interactions to Impair CXCR4 Signaling in Aging Cells

Abstract

Organismal aging is accompanied by the accumulation of senescent cells in the body, which drives tissue dysfunction. Senescent cells have a distinctive profile, including proliferation arrest, resistance to apoptosis, altered gene expression, and high inflammation. Despite global signaling and metabolic dysregulation during senescence, the underlying reasons for changes in signaling remain unclear. GPCRs are pivotal in cellular signaling, dynamically mediating the complex interplay between cells and their surrounding environment to maintain cellular homeostasis. The chemokine receptor CXCR4 plays a crucial role in modulating immune responses and inflammation. It has been shown that the expression of CXCR4 increases in cells undergoing senescence, which enhances inflammation postactivation. Here, we examine CXCR4 signaling in deeply senescent cells (aged cells), where cholesterol and its oxidized derivatives, oxysterols, affect receptor function. We report elevated oxysterol levels in senescent cells, which altered classical CXCL12-mediated CXCR4 signaling. Tail-oxidized sterols disrupted signaling more than ring-oxidized counterparts. Molecular dynamics simulations revealed that 27-hydroxycholesterol displaces cholesterol and binds strongly to alter the conformation of critical signaling residues, modifying the sterol–CXCR4 interaction landscape. Our study provides a molecular view of the observed mitigated GPCR signaling in the presence of oxysterols, which switched G-protein signaling from Gα_i/o to Gα_s class. Overall, we present an altered paradigm of GPCR signaling, where cholesterol oxidation alters the signaling outcome in aged cells.