A NEW ROLE OF COMPLEXIN2 DURING GLUT4 TRANSPORT IN MYOBLAST L6 CELLS

ZANNI RUIZ EMILIA.; MAYORGA LUIS S; KLIP AMIRA; PAVAROTTI MARTÍN A

Mendoza

Jornada; XXXVI Reunión científica anual de la Sociedad Biología de Cuyo; 2018

Sociedad de Biología de Cuyo

The GLUT4 transport is the rate-limiting process for glucose uptake and utilization in adipose and muscle tissues. The GLUT4 is the insulin-regulated glucose transporter expressed mainly in striated muscle and adipose tissues. It is well known that insulin mediates the glucose uptake by an increase of GLUT4 traffic from intracellular storage (GSVs/IRVs) to the plasma membrane, a process known as “GLUT4 translocation” or “GLUT4 exocytosis”, which is, in addition, the deficient-process in type2 diabetes. Intracellular membrane fusions are carried out by canonical SNAREs proteins, which are constitutively active and require a large set of regulatory proteins. In this regard, the calcium sensor synaptotagmin and complexin play a key role in calcium-regulated exocytosis in the neurons, neuroendocrine cells, and spermatozoa. Specifically, the t-SNAREs, sintaxin-4 and SNAP23, and the v-SNARE Vamp2 are the main SNAREs in GLUT4-exocytosis. It’s well established that this process requires calcium and calcium sensors (ESYT1 and Doc2B), however, there are non-evidences about the presence and participation of complexin during this process in muscle cells. Regarding the action mechanism of complexin, it seems is able of carrying out its functions once the SNAREs complex is partially assembled. In this way, complexin binds, stabilizes, and prevents the SNARE-complex from continuing its assembly until the membrane fusion. The transient calcium increase allows the synaptotagmin activation, which displaces the complexin from SNARE preassembled complex, allowing the final assembly and therefore the membranes fusion. Therefore, our aim was to study the presence of complexins in muscle cells and its participation in GLUT4-exocytosis. Using different approaches like western blot, immunofluorescence and qPCR we were able to show the presence of complexins in L6-muscle cells and skeletal muscle tissue, being complexin2 the most abundant isoform. Subsequently, we performed a GLUT4 translocation assay in complexin2-knockdown and complexin2-overexpressed L6 cells. The results show that the KD and overexpressed complexin2 decrease the GLUT4 translocation in L6 cells. Keywords: GLUT4 translocation, membrane fusion, SNAREs, muscle.