X-linked hypophosphatemia (XLH/HYP)-with renal phosphate wasting, hypophosphatemia, osteomalacia, and tooth abscesses-is caused by mutations in the zinc-metallopeptidase PHEX gene (phosphate-regulating gene with homologies to endopeptidase on the X chromosome). PHEX is highly expressed by mineralized tissue cells. Inactivating mutations in PHEX lead to distal renal effects (implying accumulation of a secreted, circulating phosphaturic factor) and accumulation in bone and teeth of mineralization-inhibiting, acidic serine-and aspartate-rich motif (ASARM)-containing peptides, which are proteolytically derived from the mineral-binding matrix proteins of the SIBLING family (small, integrin-binding ligand N-linked glycoproteins). Although the latter observation suggests a local, direct matrix effect for PHEX, its physiologically relevant substrate protein(s) have not been identified. Here, we investigated two SIBLING proteins containing the ASARM motif-osteopontin (OPN) and bone sialoprotein (BSP)-as potential substrates for PHEX. Using cleavage assays, gel electrophoresis, and mass spectrometry, we report that OPN is a full-length protein substrate for PHEX. Degradation of OPN was essentially complete, including hydrolysis of the ASARM motif, resulting in only very small residual fragments. Western blotting of Hyp (the murine homolog of human XLH) mouse bone extracts having no PHEX activity clearly showed accumulation of an $35 kDa OPN fragment that was not present in wild-type mouse bone. Immunohistochemistry and immunogold labeling (electron microscopy) for OPN in Hyp bone likewise showed an accumulation of OPN and/or its fragments compared with normal wild-type bone. Incubation of Hyp mouse bone extracts with PHEX resulted in the complete degradation of these fragments. In conclusion, these results identify full-length OPN and its fragments as novel, physiologically relevant substrates for PHEX, suggesting that accumulation of mineralization-inhibiting OPN fragments may contribute to the mineralization defect seen in the osteomalacic bone characteristic of XLH/HYP. ß

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Objective and design: Several proteases have drawn attention as potential targets to control the SARS-CoV-2 infection (COVID-19), thus circulating enzymatic activity and RAS regulation in severe hospitalized patients still remain to be determined. Material or subjects: 164 patients with COVID-19-like symptoms were grouped according to the severity of symptoms (COVID-19 negative, mild, moderate and severe). Methods: Patients were subjected to biochemical analyzes and to enzymatic activities of ACE2, ACE, DPPIV, PREP and CAT L, evaluated in serum samples. One-way ANOVA and multivariate logistic regression analysis were used. Statistical significance was accepted at p<0.05. Results: We show a correlation among comorbidities, elevated C-reactive protein (CRP) levels and disease severity. Additionally, concomitant high levels of D-dimer and CRP could be as prognostic for severe conditions. Assays of enzymatic activities revealed that, according to disease severity, both ACE2 and CAT L were statistically increased, while ACE, DPPIV and PREP activities were significantly reduced. Notably, analysis of ACE2/ACE ratio suggest a possible imbalance of Ang II/Ang1-7 ratio in severe patients. Conclusion: Our findings reveal the correlation between protease activity and the severity of COVID-19, in addition to highlighting the imbalance of ACE2/ACE ratio, predicting RAS dysregulation, closely related with a poor outcome of disease.