## 3 Discussion
concluded that the upregulation of miR-143, miR-215, and miR-224 in the serum of the hepatitis C virus-associated HCC patients compared with control samples could be applied not only as a diagnostic marker of the disease but also as an indicator of the grade of the tumor and the stage of fibrosis, although all three miRNAs were downregulated in liver tumor tissue compared with their control. Conversely, the development of liver fibrosis in autoimmune hepatitis was lessened by miRNA-143-3p through the regulation of TAK1 phosphorylation according to another study [39; 45]. Investigations, both _in vivo_ and _in vitro_, have suggested that miR-409-3p, along with other miRNAs, plays a crucial role in regulating the progression of human NAFLD and is a non-invasive diagnosticbiomarker of its severity and progression [46; 47]. In addition, miR-409-3p controls the angiogenesis of brown tissue and insulin resistance by regulating endothelial cell-brown adipose tissue crosstalk via a MAP4K3-ZEB1-PLGF signaling axis [48]. The expression of miR-409-3p is reduced in the tissue and cell lines of liver cancer and is negatively correlated with tumor stage, tumor size, and the survival time of patients [38]. Our luciferase reporter assay validated and confirmed that _PCSK7_ mRNA is a direct target of miR-125a-5p, miR-143-3p, and miR-409-3p. Since PC7 is implicated in liver diseases and hepatic cancer, our results suggest that these miRNAs could modulate _PCSK7_ expression in different liver diseases, likely being protective against the development of NAFLD/NAFLD [16], where PC7 seems to play a non-enzymatic role [13; 17], possibly as a chaperone for some lipoproteins such as apolipoprotein B ([PERSON] et al., _in preparation_). However, further investigations are needed to specify which miRNAs significantly regulate the expression of _PCSK7_ in different liver pathologies and/or cancers. Cirrhosis develops in <10% of individuals homozygous for the C282Y variant in the homeostatic iron regulator (HFE) gene, where a gain-of-function variant of _PCSK7_ (rs236918) [8; 49] is associated with an increased risk of cirrhosis in this patient population [18]. The various mechanism regulating PC7 are not yet defined, except that its Ser-phosphorylation can reduce its non-enzymatically induced degradation of apoA-V in the ER [13]. We previously showed that PC7 regulates iron metabolism in the liver by an enzymatic mechanism implicating the shedding hTfR1, resulting in the secretion of a circulating sTfR1 that correlates with iron deficiency [8; 49]. Our present Western blot analysis demonstrated that _PCSK7_ inhibition by miR-125a-5p reduced the shedding of hTfR1, suggesting that miR-125a-5p could reduce the enzymatic function of PC7 and inhibit the shedding of hTfR1 and could find applications in the treatment of hereditary hemochromatosis. Overall, we validated our hypothesis that the gene expression of _PCSK7_ can be downregulated by miRNAs, three of which were identified in this study. In the future, the expression of mimics of such miRNAs or others would represent a novel approach to decrease the activity of PC7 and reduce the processing of its downstream substrates, e.g., TfR1, or partners, such as apoA-V and apoB, with pharmacological applications in the treatment of fatty liver disease and dyslipidemia.