Evidence for the involvement of lipid rafts localized at the ER-mitochondria associated membranes in autophagosome formation

Abstract

Mitochondria-associated membranes (MAMs) are subdomains of the endoplasmic reticulum (ER) that interact with mitochondria. This membrane scrambling between ER and mitochondria appears to play a critical role in the earliest steps of autophagy. Recently, lipid microdomains, i.e. lipid rafts, have been identified as further actors of the autophagic process. In the present work, a series of biochemical and molecular analyses has been carried out in human fibroblasts with the specific aim of characterizing lipid rafts in MAMs and to decipher their possible implication in the autophagosome formation. In fact, the presence of lipid microdomains in MAMs has been detected and, in these structures, a molecular interaction of the ganglioside GD3, a paradigmatic "brick" of lipid rafts, with core-initiator proteins of autophagy, such as AMBRA1 and WIPI1, was revealed. This association seems thus to take place in the early phases of autophagic process in which MAMs have been hypothesized to play a key role. The functional activity of GD3 was suggested by the experiments carried out by knocking down ST8SIA1 gene expression, i.e., the synthase that leads to the ganglioside formation. This experimental condition results in fact in the impairment of the ER-mitochondria crosstalk and the subsequent hindering of autophagosome nucleation. We thus hypothesize that MAM raft-like microdomains could be pivotal in the initial organelle scrambling activity that finally leads to the formation of autophagosome.

Disease‐modifying effects of ganglioside GM1 in Huntington's disease models

“…The underlying mechanism remains to be investigated. GM1 might activate autophagy, as was shown in other disease models (Hwang et al , ; Garofalo et al , ; Dai et al , ), thus potentially facilitating autophagic degradation of mutant HTT. Future experiments will test this hypothesis.…”

A high-density human mitochondrial proximity interaction network

“…S5D) are three members of the SMCR8-C9orf72-WDR41 complex, which has been implicated in autophagosome maturation (Yang et al, 2016), selective autophagy (Sellier et al, 2016), and both positive and negative regulation of autophagy (Jung et al, 2017;Ugolino et al, 2016). The transfer of calcium from the ER to mitochondria, which occurs at contact sites, regulates autophagosome formation (Gomez-Suaga et al, 2017;Mallilankaraman et al, 2012;Vicencio et al, 2009;Wong et al, 2013), and autophagosomes form at sites of apposition between ER and mitochondria (Garofalo et al, 2016;Hailey et al, 2010;Hamasaki et al, 2013), all consistent with the presence of the SMCR8-C9orf72-WDR41 complex at mitochondria-ER contact sites.…”

The regulatory roles of glycosphingolipid‐enriched lipid rafts in immune systems

“…Formation of autophagosomes at the endoplasmic reticulum–mitochondria contact site [mitochondria‐associated membranes (MAM)] in mammalian cells has been suggested . Recently, GD3 was shown to form lipid raft‐like domains in MAM and to interact with core‐initiator proteins of autophagy. These observations suggest that lipid raft‐like domains in MAM are important in the organelle scrambling activity that leads to autophagosome biogenesis.…”