Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Göritzer, M.
Role of CGI-58 in macrophages and
Autophagy in lipase-deficient macrophages
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Graz Medical University; 2015. pp.
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- Autor*innen der Med Uni Graz:
- Göritzer Madeleine
- Betreuer*innen:
- Kratky Dagmar
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- Abstract:
- Cellular triglyceride (TG) stores are efficiently hydrolyzed by adipose triglyceride lipase (ATGL). Its co-activator comparative gene identification-58 (CGI-58) strongly increases ATGL-mediated TG catabolism in cell culture experiments. In humans, mutations of CGI-58 cause Chanarin-Dorfman-Syndrome resulting in ichthyosis and TG accumulation in essentially all tissues. Since CGI-58 knockout (-/-) mice die soon after birth due to a severe skin barrier defect we generated myeloid-specific CGI-58 (macCGI-58)-/- mice to elucidate the consequences of CGI-58 deficiency in murine macrophages. These mice are viable with no apparent changes in skin phenotype. CGI-58-/- macrophages accumulate intracellular TG-rich lipid droplets (LDs) and have decreased phagocytic capacity, comparable to ATGL-/- macrophages. In contrast to ATGL-/- macrophages, however, CGI-58-/- macrophages have intact mitochondria and show no indications of mitochondrial apoptosis and endplasmic reticulum (ER) stress. Another notable difference is the fact that CGI-58-/- macrophages adopted an M1-like phenotype in vitro. Finally, we investigated atherosclerosis susceptibility in macCGI-58/ApoE-double knockout (DKO) animals. In response to high fat/high cholesterol diet feeding, DKO animals showed comparable plaque formation in aortic root sections as observed in ApoE-/- mice. In agreement, antisense oligonucleotide-mediated knockdown of CGI-58 in low-density lipoprotein receptor-/- mice did not alter atherosclerosis burden in the aortic root. These results suggest that (despite comparable TG accumulation by ATGL and CGI-58 deficiency) macrophage function and atherosclerosis susceptibility differ fundamentally in these two animal models with disturbed TG homeostasis. During autophagy, autophagosomes fuse with lysosomes to degrade damaged organelles and misfolded proteins. Breakdown products are released into the cytosol and contribute to energy and metabolic building block supply, especially during starvation. Lipophagy has been defined as the autophagy-mediated degradation of LDs by lysosomal acid lipase. Most organs and cells, including macrophages, lacking ATGL accumulate TGs, resulting in reduced intracellular free fatty acid concentrations. Macrophages deficient in hormone-sensitive lipase (H0) do not accumulate TG albeit reduced in vitro TG hydrolase activity. We hypothesized that autophagy is activated in lipase-deficient macrophages to counteract their energy deficit. We therefore generated mice with loss of both ATGL and HSL (A0H0). Macrophages from A0H0 mice showed 73% reduced neutral TG hydrolase activity, resulting in TG-rich LD accumulation. Increased expression of cathepsin B, accumulation of LC3-II, reduced expression of p62, and increased DQ-BSA dequenching suggest intact autophagy and functional lysosomes in A0H0 macrophages. Markedly decreased acid TG hydrolase activity and lipid flux independent of bafilomycin A1 treatment, however, argue against effective lysosomal degradation of LDs in A0H0 macrophages. We conclude that autophagy of proteins and cell organelles but not of LDs is active as a compensatory mechanism to circumvent and balance the reduced availability of energy substrates in A0H0 macrophages.