Tunneling Nanotube (TNT) Mediated Intercellular Crosstalk and Autophagy in Hypoxia-Induced Mesenchymal Stem Cells

Intercellular communication is a critical process and multicellular organisms rely on communication networks to coordinate and maintain physiological functions. Tunneling nanotubes (TNTs) defined as a novel cell to cell communication mechanism and characterized by F-actin. TNTs allow the rapid exchange of cellular cargos including organelles, vesicles, molecules etc. Hypoxia plays an essential role in stem cell functions and also a known stimulus of autophagy. Autophagy and Wnt/β-catenin signalling pathways have important roles during essential cellular processes like tissue homeostasis. This study was aimed to investigate the effect of hypoxia on autophagy, Wnt/β-catenin signalling and the formation of TNTs in bone marrow mesenchymal stem cells (BM-MSCs). Western blotting was applied for HIF-1α protein expression. Immunolabeling was applied to investigate LC3B, p62 and β-catenin protein expressions. Immunofluorescence staining was assessed to evaluate TNT formations and HIF-1α protein. HIF-1α protein expression was significantly increased in CoCl2 induced hypoxic BM-MSCs compared to the normoxia. As a result of the immunofluorescence staining, HIF-1α was positively stained in the cell nuclei of hypoxic BM-MSCs. Number and lengths of TNT formations was increased in hypoxic BM-MSCs compared to the normoxia. Also, we showed that hypoxia upregulates LC3B and downregulates p62 expression. In conclusion, our study indicates that TNT-mediated intercellular communication increases under the hypoxia in BM-MSCs and hypoxic microenvironment may be a significant factor for stem cell functions. Our findings may also draw attention to a possible TNT-mediated crosstalk for autophagy and Wnt/β-catenin signalling mechanism between distant cells.