Angiopoietin-like 3 (ANGPTL3) is a hepatokine acting as a negative regulator of lipoprotein lipase (LPL). Vupanorsen, an ANGPTL3 directed antisense oligonucleotide, showed an unexpected increase in liver fat content in humans. Here, we investigated the molecular mechanism linking ANGPTL3 silencing to hepatocyte fat accumulation. Human hepatocarcinoma Huh7 cells were treated with small interfering RNA (siRNA) directed to ANGPTL3, human recombinant ANGPTL3 (recANGPTL3), or their combination. Using Western blot, Oil Red-O, biochemical assays, and ELISA, we analyzed the expression of genes and proteins involved in lipid metabolism. Oil Red-O staining demonstrated that lipid content increased after 48 h of ANGPTL3 silencing (5.89 ± 0.33 fold), incubation with recANGPTL3 (4.08 ± 0.35 fold), or their combination (8.56 ± 0.18 fold), compared to untreated cells. This effect was also confirmed in Huh7-LX2 spheroids. A total of 48 h of ANGPTL3 silencing induced the expression of genes involved in the de novo lipogenesis, such as fatty acid synthase, stearoyl-CoA desaturase, ATP citrate lyase, and Acetyl-Coenzyme A Carboxylase 1 together with the proprotein convertase subtilisin/kexin 9 (PCSK9). Time-course experiments revealed that 6 h post transfection with ANGPTL3-siRNA, the cholesterol esterification by Acyl-coenzyme A cholesterol acyltransferase (ACAT) was reduced, as well as total cholesterol content, while an opposite effect was observed at 48 h. Under the same experimental conditions, no differences in secreted apoB and PCSK9 were observed. Since PCSK9 was altered by the treatment, we tested a possible co-regulation between the two genes. The effect of ANGPTL3-siRNA on the expression of genes involved in the de novo lipogenesis was not counteracted by gene silencing of PCSK9. In conclusion, our in vitro study suggests that ANGPTL3 silencing determines lipid accumulation in Huh7 cells by inducing the de novo lipogenesis independently from PCSK9.

The Niemann-Pick type 1 and 2 proteins (NPC1 and NPC2) coordinate cholesterol egress from late endosomes-lysosomes (LE/LY). Proper folding, trafficking, and localization of both NPC proteins are essential for normal LE/LY cholesterol handling. Accordingly, mutations in NPC genes cause Niemann–Pick type C (NPC) disease, a progressive neurodegenerative lysosomal cholesterol storage disorder. The routes by which NPC1 reaches the LE/LY compartment in mammalian cells are not fully elucidated. Therefore, to interrogate NPC1 trafficking, we developed genome-engineered HeLa cells expressing endogenous NPC1 ^mNeon . We demonstrate that endogenous NPC1 localizes to the LE/LY compartment and by using protein proximity-based approaches that NPC1 resides in the same membranes as Vacuolar Protein Sorting-associated protein 41 (VPS41), one of the two unique subunits of the homotypic fusion and vacuole protein sorting complex. Loss of VPS41 increases NPC1 and Lysosomal Associated Membrane Protein 1 (LAMP1) abundance. Paradoxically, this results in marked accumulation of lysosomal cholesterol and induction of sterol regulatory element-binding protein signaling. Mechanistically, using immuno-fluorescence and electron microscopy imaging in combination with a VPS41-dependent ectopic recruitment assay, we demonstrate that this is due to a shift in the localization of NPC1 and LAMP1 from LE/LY to biosynthetic vesicles called LAMP carriers. These vesicles have been recently described to transport lysosomal-destined cargo directly from the trans- Golgi (TGN) network to LE/LY. In conclusion, we identify NPC1 as a cargo for VPS41-dependent LAMP carriers that are instrumental for the delivery of NPC1 to LE/LY and maintaining cellular cholesterol homeostasis.

Background and aim: ANGPTL3 is a hepatokine acting as a negative regulator of lipoprotein lipase (LPL) through its N-terminal domain. Besides this activity, the C-terminal domain of ANGPTL3 interacts with integrin αVβ3. Since integrins are involved in inflammation and in the initiation of atherosclerotic plaque, the aim of our study was to evaluate the potential direct pro-inflammatory action of ANGPTL3 through the interaction of the fibrinogen-like domain and integrin αVβ3. Methods: We utilized cultured THP-1 human-derived macrophages and evaluated their pro-inflammatory phenotype in response to treatment with human recombinant ANGPTL3 (hANGPTL3). By Western blot, RT-qPCR, biochemical analysis, and ELISA assays, we determined the expression of genes and proteins involved in lipid metabolism and inflammatory response as well as intracellular cholesterol and triglyceride levels. In addition, we evaluated the effect of hANGPTL3 on the cellular cholesterol efflux process. Results: Incubation of THP-1-derived macrophages with 100 ng/mL of hANGPTL3 increased the mRNA expression of the pro-inflammatory cytokines IL-1β, IL-6, and TNFα (respectively, 1.87 ± 0.08-fold, 1.35 ± 0.11-fold, and 2.49 ± 0.43-fold vs. control). The secretion of TNFα, determined by an ELISA assay, was also induced by hANGPTL3 (1.98 ± 0.4-fold vs. control). The pro-inflammatory effect of hANGPTL3 was partially counteracted by co-treatment with the integrin αVβ3 inhibitor RGD peptide, reducing the mRNA levels of IL-1β (3.35 ± 0.35-fold vs. 2.54 ± 0.25-fold for hANGPTL3 vs. hANGPTL3 + RGD, respectively). Moreover, hANGPTL3 reduced cholesterol efflux to apoA-I, with a parallel increase in the intracellular triglyceride and cholesterol contents by 31.2 ± 2.8% and 20.0 ± 4.1%, respectively, compared to the control. Conclusions: ANGPTL3 is an important liver-derived regulator of plasma lipoprotein metabolism, and overall, our results add a new important pro-inflammatory activity of this circulating protein. This new function of ANGPTL3 could also be related to triglyceride and cholesterol accumulation into macrophages.

Background: Angiopoietin-like 3 (ANGPTL3) and proprotein convertase subtilisin/kexin type 9 (PCSK9) are key regulators of lipid homeostasis. We have previously shown that gene silencing of ANGPTL3 significantly induces PCSK9 expression in the human hepatoma cell line Huh7. Here, we investigated the biological significance of this regulation in the cultured human hepatoma cell line Huh7. Methods: We performed an RNA-seq analysis in Huh7 cells transfected with siRNA-ANGPTL3, siRNA-PCSK9, and double siRNA-ANGPTL3/PCSK9. Selected findings were assessed by RT-qPCR, Western blotting, and ELISA. Results: Among 13,945 detected transcripts, 192 genes were differentially expressed after ANGPTL3 silencing, 88 after PCSK9 silencing, and 219 after combined ANGPTL3/PCSK9 silencing, compared with scramble-siRNA controls. When ANGPTL3 gene expression was silenced, we observed a compensatory induction in PCSK9 mRNA and protein expression. Bioinformatic analysis revealed that gene silencing of ANGPTL3 or both ANGPTL3/PCSK9 suppresses serpin family A member 1 (SERPINA1), which encodes α1-antitrypsin, and lectin mannose-binding 1 (LMAN1). These data were confirmed by Western blot and RT-PCR analysis. In addition, ANGPTL3-siRNA, alone or combined with PCSK9-siRNA, significantly increased FV and FVIII mRNA expression and secretion in conditioned medium. Conclusions: Our data identified SERPINA1 and LMAN1 as genes downregulated in response to ANGPTL3 silencing in Huh7 hepatoma cells, which was also associated with increased expression of FV and FVIII. Our study suggests a potential link between ANGPTL3 silencing and coagulation-related processes, extending the biological relevance of ANGPTL3 beyond lipid metabolism.