Dissociation of the insulin receptor and caveolin-1 complex by ganglioside GM3 in the state of insulin resistance

TLDR

Membrane microdomains (lipid rafts) are critical for compartmentalizing insulin signaling. The study aims to elucidate how insulin receptor (IR), caveolin‑1 (Cav1), and ganglioside GM3 interact in adipocytes and to propose that GM3‑mediated dissociation of the IR‑Cav1 complex underlies insulin resistance. Immunoprecipitation, cross‑linking, total internal reflection fluorescence microscopy, and fluorescence recovery after photobleaching were used to examine IR, Cav1, and GM3 interactions and IR mobility. GM3 accumulation in insulin‑resistant adipocytes causes dissociation of the IR‑Cav1 complex, increases IR mobility, and requires a lysine residue above the IR β‑subunit transmembrane domain for IR‑GM3 binding, providing a mechanistic basis for insulin resistance.

Abstract

Membrane microdomains (lipid rafts) are now recognized as critical for proper compartmentalization of insulin signaling. We previously demonstrated that, in adipocytes in a state of TNFalpha-induced insulin resistance, the inhibition of insulin metabolic signaling and the elimination of insulin receptors (IR) from the caveolae microdomains were associated with an accumulation of the ganglioside GM3. To gain insight into molecular mechanisms behind interactions of IR, caveolin-1 (Cav1), and GM3 in adipocytes, we have performed immunoprecipitations, cross-linking studies of IR and GM3, and live cell studies using total internal reflection fluorescence microscopy and fluorescence recovery after photobleaching techniques. We found that (i) IR form complexes with Cav1 and GM3 independently; (ii) in GM3-enriched membranes the mobility of IR is increased by dissociation of the IR-Cav1 interaction; and (iii) the lysine residue localized just above the transmembrane domain of the IR beta-subunit is essential for the interaction of IR with GM3. Because insulin metabolic signal transduction in adipocytes is known to be critically dependent on caveolae, we propose a pathological feature of insulin resistance in adipocytes caused by dissociation of the IR-Cav1 complex by the interactions of IR with GM3 in microdomains.