Bcl-2-associated athanogen-6 (BAG6) is a nucleocytoplasmic shuttling protein involved in protein quality control. We previously demonstrated that BAG6 is essential for autophagy by regulating the intracellular localization of the acetyltransferase EP300, and thus, modifying accessibility to its substrates (TP53 in the nucleus and autophagy-related proteins in the cytoplasm). Here, we investigated BAG6 localization and function in the cytoplasm. First, we demonstrated that BAG6 is localized in the mitochondria. Specifically, BAG6 is expressed in the mitochondrial matrix under basal conditions, and translocates to the outer mitochondrial membrane after mitochondrial depolarization with carbonyl cyanide m-chlorophenyl hydrazine, a mitochondrial uncoupler that induces mitophagy. In SW480 cells, the deletion of BAG6 expression abrogates its ability to induce mitophagy and PINK1 accumulation. On the reverse, its ectopic expression in LoVo colon cancer cells, which do not express endogenous BAG6, reduces the size of the mitochondria, induces mitophagy, leads to the activation of the PINK1/PARKIN pathway and to the phospho-ubiquitination of mitochondrial proteins. Finally, BAG6 contains two LIR (LC3-interacting Region) domains specifically found in receptors for selective autophagy and responsible for the interaction with LC3 and for autophagosome selectivity. Site-directed 2 of 14 | RAGIMBEAU Et Al.
Lyl1 encodes a hematopoietic- and endothelial-specific bHLH transcription factor. Lyl1-deficient mice are viable, but they display mild hematopoietic and vascular defects. Specifically, LYL1 is required for the maturation and stabilization of blood vessel endothelial adherens junctions. Here, we report that young adult Lyl1−/− mice exhibit transient overweight associated with general expansion of adipose tissue, without signs of metabolic disorder and unrelated to food intake. The increased fat tissue development in Lyl1−/− mice resulted from earlier differentiation of adipose stem cells (ASCs) into adipocytes through noncell autonomous mechanisms. Specifically, we found that in Lyl1−/− mice, the adipose tissue vascular structures are immature, as indicated by their high permeability, reduced coverage by pericytes, lower recruitment of VE-cadherin and ZO1 at cell junctions, and more prone to angiogenesis. Together, our data show that in Lyl1−/− mice, the impaired vascular compartment of the adipose niche promotes ASC differentiation, leading to early adipocyte expansion and premature ASC depletion. Our study highlights the major structural role of the adipose tissue vascular niche in coordinating stem cell self-renewal and differentiation into adipocytes.
Lymphoblastic leukemia-derived sequence 1 (Lyl1) encodes a hematopoietic-and endothelial-specific transcriptional factor. Lyl1-deficient mice are viable, but they display mild hematopoietic and vascular defects. Here, we report that young Lyl1 -/mice exhibit transient obesity associated with general expansion of adipose tissues and unrelated to food intake.The increased fat tissue development in Lyl1 -/mice resulted from an earlier adipocyte differentiation of adipose stem cells (ASCs) through non-cell autonomous mechanisms.Specifically, we found that in Lyl1 -/mice, the vascular structures of adipose tissues are unstable, more prone to angiogenesis and, consequently, cannot maintain adipose progenitors in the niche vessel wall. Together, our data show that in Lyl1 -/mice, the impaired vascular compartment of the adipose niche promotes uncontrolled ASC activation and differentiation, leading to early adipocyte expansion and premature depletion of ASCs. Our study highlights the major structural role of the adipose tissue vascular niche in coordinating stem cell self-renewal and differentiation into adipocytes.
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