GDF-15 Deficiency Reduces Autophagic Activity in Human Macrophages In Vitro and Decreases p62-Accumulation in Atherosclerotic Lesions in Mice.

(1) Background: Growth differentiation factor-15 (GDF-15) is associated with cardiovascular diseases and autophagy in human macrophages (MΦ). Thus, we are interested in investigating autophagic mechanisms with special respect to the role of GDF-15. (2) Methods: Recombinant (r)GDF-15 and siRNA GDF-15 were used to investigate the effects of GDF-15 on autophagic and lysosomal activity, as well as autophagosome formation by transmission electron microscopy (TEM) in MΦ. To ascertain the effects of GDF-15-/- on the progression of atherosclerotic lesions, we used GDF-15-/-/ApoE-/- and ApoE-/- mice under a cholesterol-enriched diet (CED). Body weight, body mass index (BMI), blood lipid levels and lumen stenosis in the brachiocephalic trunk (BT) were analyzed. Identification of different cell types and localization of autophagy-relevant proteins in atherosclerotic plaques were performed by immunofluorescence. (3) Results: siGDF-15 reduced and, conversely, rGDF-15 increased the autophagic activity in MΦ, whereas lysosomal activity was unaffected. Autophagic degradation after starvation and rGDF-15 treatment was observed by TEM. GDF-15-/-/ApoE-/- mice, after CED, showed reduced lumen stenosis in the BT, while body weight, BMI and triglycerides were increased compared with ApoE-/- mice. GDF-15-/- decreased p62-accumulation in atherosclerotic lesions, especially in endothelial cells (ECs). (4) Conclusion: GDF-15 seems to be an important factor in the regulation of autophagy, especially in ECs of atherosclerotic lesions, indicating its crucial pathophysiological function during atherosclerosis development.

Data on autophagy markers in human macrophages exposed to oxLDL and growth differentiation factor-15.

Growth differentiation factor-15 (GDF-15) is a member of the TGF-ß superfamily, identical to MΦ-inhibitory cytokine-1 (MIC-1). GDF-15 is associated with e.g. cardiovascular disease, inflammation and development of atherosclerosis and is highly expressed in macrophages (MΦ) of atherosclerotic lesions. Moreover, there exists an indication for the involvement of oxidized-low density lipoprotein (oxLDL) uptake and autophagic processes by MΦ regarding arteriosclerotic progression. Thus, we were interested to investigate a potential regulatory effect of GDF-15 on autophagy signaling pathway in human MΦ during foam cell formation. Here, we present western blot data of ATG5, ATG12/ATG5-complex and p62 regarding the GDF-15 concentration. For further interpretation of the data presented in this article, please see the research article "Growth differentiation factor-15 regulates oxLDL-induced lipid homeostasis and autophagy in human macrophages" [1].

Growth differentiation factor-15 regulates oxLDL-induced lipid homeostasis and autophagy in human macrophages.

BACKGROUND AND AIMS: Growth differentiation factor-15 (GDF-15)/macrophage inhibitory cytokine-1 (MIC-1/GDF15) is associated with cardiovascular disease, inflammation and development of atherosclerosis and is highly expressed in macrophages (MΦ) of atherosclerotic lesions. Thus, we were interested in investigating the influence of GDF-15 in lipid homeostasis and autophagy in human MΦ during foam cell formation. METHODS AND RESULTS: Oxidized-low density lipoprotein (50 µg/ml oxLDL), recombinant (r)GDF-15, transiently silenced GDF-15 (siGDF-15 MΦ), as well as with negative siRNA transfected (nsiGDF-15 MΦ) PMA-differentiated human THP-1 MΦ, were used to investigate the effects of GDF-15 on autophagic processes and lipid accumulation. Oil Red O staining revealed that rGDF-15 alone, but also in combination with oxLDL, significantly increased the lipid accumulation in THP-1 MΦ; a reverse effect was detected in siGDF-15 MΦ. Western-blot analyses and confocal laser scanning microscopy showed an increase of Atg5, Atg12/Atg5 protein complex and p62 protein in THP-1 MΦ co-incubated with rGDF-15 and oxLDL, as well as an increase of p62 accumulation compared to rGDF-15-treated MΦ. Vice versa, siGDF-15 MΦ showed a reduced p62 accumulation compared to nsiGDF-15 MΦ. The present study indicates that GDF-15, especially in combination with oxLDL, regulates the expression of autophagy-relevant proteins (p62, Atg5 and Atg12/Atg5 protein complex) and p62 accumulation in human MΦ. CONCLUSIONS: GDF-15, in combination with oxLDL, impairs autophagic processes with consequences for lipid homeostasis in human MΦ, indicating its novel important pathophysiological role in atherosclerotic plaque development and progression.

Comparative toxicity of nanoparticulate CuO and ZnO to soil bacterial communities.

The increasing industrial application of metal oxide Engineered Nano-Particles (ENPs) is likely to increase their environmental release to soils. While the potential of metal oxide ENPs as environmental toxicants has been shown, lack of suitable control treatments have compromised the power of many previous assessments. We evaluated the ecotoxicity of ENP (nano) forms of Zn and Cu oxides in two different soils by measuring their ability to inhibit bacterial growth. We could show a direct acute toxicity of nano-CuO acting on soil bacteria while the macroparticulate (bulk) form of CuO was not toxic. In comparison, CuSO(4) was more toxic than either oxide form. Unlike Cu, all forms of Zn were toxic to soil bacteria, and the bulk-ZnO was more toxic than the nano-ZnO. The ZnSO(4) addition was not consistently more toxic than the oxide forms. Consistently, we found a tight link between the dissolved concentration of metal in solution and the inhibition of bacterial growth. The inconsistent toxicological response between soils could be explained by different resulting concentrations of metals in soil solution. Our findings suggested that the principal mechanism of toxicity was dissolution of metal oxides and sulphates into a metal ion form known to be highly toxic to bacteria, and not a direct effect of nano-sized particles acting on bacteria. We propose that integrated efforts toward directly assessing bioavailable metal concentrations are more valuable than spending resources to reassess ecotoxicology of ENPs separately from general metal toxicity.