Active autophagy but not lipophagy in macrophages with defective lipolysis.
Bottom Line: Macrophages from A0H0 mice showed 73% reduced neutral TG hydrolase activity, resulting in TG-rich LD accumulation.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.
Affiliation: Institute of Molecular Biology & Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21, 8010 Graz, Austria.Show MeSH
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Mentions: To investigate the rate of LD accumulation in A0H0 macrophages, we analyzed intracellular TG and cholesterol concentrations. We observed ~3-fold increased TG concentrations in A0 and A0H0 macrophages compared to Wt and H0 macrophages (Fig. 2A). TG content in H0 and Wt macrophages was comparable, indicating that the absence of HSL failed to affect intracellular TG stores in A0H0 macrophages (Fig. 2A). In accordance with our previous findings in H0  and A0 macrophages , TC concentrations were unchanged in A0H0 compared to Wt macrophages (Fig. 2B). To determine the LD content, we analyzed the cells after Nile red staining by fluorescence microscopy. Macrophages from A0 and A0H0 mice had substantially more LDs compared with macrophages from Wt and H0 mice (Fig. 2C, D). HSL deficiency did not lead to noticeable alterations in the amount of LDs, neither in A0H0 compared with A0 nor in H0 compared with Wt macrophages.
Affiliation: Institute of Molecular Biology & Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21, 8010 Graz, Austria.