Search

The hypothalamus regulates feeding and glucose homeostasis through the balanced action of different neuropeptides, which are cleaved and activated by the proprotein convertases PC1/3 and PC2. However, the recent association of polymorphisms in the proprotein convertase FURIN with type 2 diabetes, metabolic syndrome, and obesity, prompted us to investigate the role of FURIN in hypothalamic neurons controlling glucose and feeding. POMC-Cre+/− mice were bred with Furin fl/fl mice to generate conditional knockout mice with Furin- deletion in neurons expressing proopiomelanocortin (POMC Fur KO), and Furin fl/fl mice were used as controls. POMC Fur KO and controls were periodically monitored on both normal chow diet and high fat diet (HFD) for body weight and glucose tolerance by established in-vivo procedures. Food intake was measured in HFD-fed Fur KO and controls. Hypothalamic Pomc mRNA was measured by RT-qPCR. ELISAs quantified POMC protein and resulting peptides in the hypothalamic extracts of POMC Fur KO mice and controls. The in-vitro processing of POMC was studied by biochemical techniques in HEK293T and CHO cell lines lacking FURIN. In control mice, Furin mRNA levels were significantly upregulated on HFD feeding, suggesting an increased demand for FURIN activity in obesogenic conditions. Under these conditions, the POMC Fur KO mice were hyperphagic and had increased body weight compared to Furin fl/fl mice. Moreover, protein levels of POMC were elevated and ACTH concentrations markedly reduced. Also, the ratio of α-MSH/POMC was decreased in POMC Fur KO mice compared to controls. This indicates that POMC processing was significantly reduced in the hypothalami of POMC Fur KO mice, highlighting for the first time the involvement of FURIN in the cleavage of POMC. Importantly, we found that in vitro , the first stage in processing where POMC is cleaved into proACTH was achieved by FURIN but not by PC1/3 or the other proprotein convertases in cell lines lacking a regulated secretory pathway. These results suggest that FURIN processes POMC into proACTH before sorting into the regulated secretory pathway, challenging the dogma that PC1/3 and PC2 are the only convertases responsible for POMC cleavage. Furthermore, its deletion affects feeding behaviors under obesogenic conditions. • Hypothalamic Furin mRNA levels were significantly upregulated on high-fat feeding. • High-fat diet fed mice lacking Furin in POMC neurons were hyperphagic and had increased body weight. • POMC processing to proACTH was significantly reduced in the hypothalami of mice lacking Furin in POMC neurons. • FURIN is a POMC-processing enzyme. [ABSTRACT FROM AUTHOR]

Abstract: Background: Proprotein convertase subtilisin/kexin (PCSK) enzymes cleave proproteins into mature end products. Previously, MBTPS1 and PCSK9 have been shown to regulate cholesterol metabolism and LDL receptor recycling, whereas FURIN and PCSK5 have been suggested to inactivate lipases and regulate inflammation in atherosclerosis. Here, we systematically analyzed the expression of PCSKs and their targets in advanced atherosclerotic plaques. Methods and results: Microarray and quantitative real-time PCR experiments showed that FURIN (42.86 median fold, p =2.1e−8), but no other PCSK, is universally overexpressed in the plaques of different vascular regions. The mRNA expression screen of PCSK target proteins in plaques identified many known factors, but it also identified the significant upregulation of the previously overlooked furin-processed B cell activating cytokines APRIL (TNFSF13, 2.52 median fold, p =3.0e−5) and BAFF (TNFSF13B, 2.97 median fold, p =7.6e−6). The dysregulation of FURIN did not associate with its htSNPs or the previously reported regulatory SNP (−229, rs4932178) in the promoter. Immunohistochemistry experiments showed the upregulation of FURIN in the plaque lymphocytes and macrophages where it was co-expressed with BAFF/TNFSF13B and APRIL/TNFSF13. Conclusions: Our data unequivocally show that FURIN is the primary PCSK that is dysregulated in the immune cells of advanced human atherosclerotic plaques, which implies a role for this enzyme in plaque pathology. Therefore, drugs that inhibit FURIN in arteries may modulate the course of this disease. [Copyright &y& Elsevier]