IMPAIRED ACE2 GLYCOSYLATION AND PROTEASE ACTIVITY LOWERS SUSCEPTIBILITY TO SARS-COV-2 INFECTION IN GITELMAN/BARTTER SYNDROMES

Abstract

Objective: ACE2, part of the counterregulatory arm of the ennin-angiotensin system, serves both as protective toward oxidative stress and cardiovascular enninling and as key entry for SARS-CoV-2. ACE2 has two isoforms, non-glycosylated and glycosylated, being this latter accountable for the binding with SARS-CoV-2. After the binding, viruses use proteases as cathepsin-L (Cat-L) to entry the cells. Both ACE2 glycosylation and Cat-L activity are pH-dependent. Gitelman and Bartter syndromes (GS/BS), rare genetic tubulopathies, are characterized by electrolytic alterations, activation of the ennin-angiotensin system, yet normo-hypotension, increased levels of ACE2 and metabolic alkalosis with likely increased intracellular pH. We reported that during the first wave of COVID-19 in early 2020 none of our cohort of 128 GS/BS patients from the major hotspots in Northern Italy had been infected or suffered any major COVID-19 symptoms and in a second survey on the same cohort in 2021 we reported only 8 positives, 4 asymptomatic and 4 with very light symptoms This study aims to investigate potential mechanisms as ACE2 glycosylation and Cat-L activity related to patients’ metabolic alkalosis and viral entry/infection. Design and method: Mononuclear cells ACE2 glycosylation (Western blot) and blood Cat-L activity (ELISA) from 20 GS/BS patients have been compared to those from 15 heathy subjects. Results: Non-glycosylated ACE2 was higher in GS/BS (0.82 ± 0.19 d.u. vs 0.67 ± 0.13 p = 0.01); glycosylated ACE2 was not different (0.85 ± 0.28 in GS/BS vs 0.73 ± 0.23 p = 0.19). Cat-L activity was lower in GS/BS (3.90 ± 1.13 r.f.u. vs 5.31 ± 0.8 p < 0.001) and inversely correlated with blood bicarbonate (HCO3-), while a negative correlation between glycosylated ACE2 and HCO3- approaches statistical significance (p = 0.08). Conclusions: GS/BS's metabolic alkalosis, likely by increasing intracellular pH, influences the glycosylation of ACE2 and the activity of Cat-L, providing a mechanistic explanation for the near complete absence of COVID-19 or its symptoms reported in our cohort. These findings provide a rationale for pursuing the identification and/or synthesis of new drugs that specifically target ACE2 glycosylation and/or proteases involved in SARS-CoV-2 infection.