Plasma apolipoprotein C1 concentration is associated with plasma triglyceride concentration but not with visceral fat and liver fat content in people with type 1 diabetes

ApoC1 promotes glioma metastasis by enhancing epithelial-mesenchymal transition and activating the STAT3 pathway

OBJECTIVE

One of the apolipoprotein's members, apolipoprotein C1 (ApoC1), is critical in the metabolism of both very-low-density lipoprotein (VLDL) and high-density lipoprotein (HDL) cholesterols. Multiple studies have recently revealed that ApoC1 may be a viable therapeutic target in solid malignancies. However, the motor protein ApoC1's specific role and mechanism in glioblastoma remain unknown.

METHODS

In this study, the Cancer Genome Atlas (TCGA) database was used to look at the level of ApoC1 in glioma tissues and normal tissues, as well as how it related to the prognosis of glioma. Glioma cell lines (U87 and U251) were subjected to a wide range of experiments to determine the involvement of ApoC1 in cell proliferation, migration, and invasion.

RESULTS

Cell proliferation, migration, and invasion decreased in glioma cell lines when ApoC1 was silenced. Furthermore, ApoC1 increased glioma cell metastasis through the epithelial-mesenchymal transition (EMT), while ApoC1 deletion reduced this impact. Additionally, APOC1 influenced the evolution of glioma by affecting the STAT3 pathway. In addition, APOC1 knockdown reduced the activation of the phosphorylated-total signal transducer and activator of transcription (STAT3) in the glioma cells. ApoC1-induced glioma cell metastatic ability was prevented by niclosamide (a STAT3 inhibitor).

CONCLUSIONS

These results uncover that ApoC1 may serve as a biomarker or therapeutic target for future fundamental study or clinical treatment of glioma.

Role of apolipoprotein C1 in lipoprotein metabolism, atherosclerosis and diabetes: a systematic review

Apolipoprotein C1 (apoC1) is a small size apolipoprotein whose exact role is not totally clarified but which seems to modulate significantly the metabolism of lipoproteins. ApoC1 is involved in the metabolism of triglyceride-rich lipoproteins by inhibiting the binding of very low density lipoproteins (VLDL) to VLDL-receptor (VLDL-R), to low density lipoprotein receptor (LDL-R) and to LDL receptor related protein (LRP), by reducing the activity of lipoprotein lipase (LPL) and by stimulating VLDL production, all these effects leading to increase plasma triglycerides. ApoC1 takes also part in the metabolism of high density lipoproteins (HDL) by inhibiting Cholesterol Ester Transfer Protein (CETP). The functionality of apoC1 on CETP activity is impaired in diabetes that might account, at least in part, for the increased plasma CETP activity observed in patients with diabetes. Its different effects on lipoprotein metabolism with a possible role in the modulation of inflammation makes the net impact of apoC1 on cardiometabolic risk difficult to figure out and apoC1 might be considered as pro-atherogenic or anti-atherogenic depending on the overall metabolic context. Making the link between total plasma apoC1 levels and the risk of cardio-metabolic diseases is difficult due to the high exchangeability of this small protein whose biological effects might depend essentially on its association with VLDL or HDL. The role of apoC1 in humans is not entirely elucidated and further studies are needed to determine its precise role in lipid metabolism and its possible pleiotropic effects on inflammation and vascular wall biology. In this review, we will present data on apoC1 structure and distribution among lipoproteins, on the effects of apoC1 on VLDL metabolism and HDL metabolism and we will discuss the possible links between apoC1, atherosclerosis and diabetes.

Apolipoprotein C1: Its Pleiotropic Effects in Lipid Metabolism and Beyond

Apolipoprotein C1 (apoC1), the smallest of all apolipoproteins, participates in lipid transport and metabolism. In humans, APOC1 gene is in linkage disequilibrium with APOE gene on chromosome 19, a proximity that spurred its investigation. Apolipoprotein C1 associates with triglyceride-rich lipoproteins and HDL and exchanges between lipoprotein classes. These interactions occur via amphipathic helix motifs, as demonstrated by biophysical studies on the wild-type polypeptide and representative mutants. Apolipoprotein C1 acts on lipoprotein receptors by inhibiting binding mediated by apolipoprotein E, and modulating the activities of several enzymes. Thus, apoC1 downregulates lipoprotein lipase, hepatic lipase, phospholipase A2, cholesterylester transfer protein, and activates lecithin-cholesterol acyl transferase. By controlling the plasma levels of lipids, apoC1 relates directly to cardiovascular physiology, but its activity extends beyond, to inflammation and immunity, sepsis, diabetes, cancer, viral infectivity, and-not last-to cognition. Such correlations were established based on studies using transgenic mice, associated in the recent years with GWAS, transcriptomic and proteomic analyses. The presence of a duplicate gene, pseudogene APOC1P, stimulated evolutionary studies and more recently, the regulatory properties of the corresponding non-coding RNA are steadily emerging. Nonetheless, this prototypical apolipoprotein is still underexplored and deserves further research for understanding its physiology and exploiting its therapeutic potential.