CEREBROVASCULAR COMPLICATIONS OF SARS-CoV-2 IN TYPE-2 DIABETES

Abstract

Diabetics are more vulnerable to SARS-CoV-2 cerebrovascular complications, including brain fog, cognitive impairment, and strokes. This study aims to identify the molecular mechanisms of SARS-CoV-2-induced cerebrovascular dysfunction in diabetics. We hypothesize that SARS-CoV-2 exacerbates diabetes-induced cerebral oxidative stress and inflammation via activation of the destructive arm of the renin-angiotensin system (RAAS) and toll-like receptor (TLR) signaling.

Methods: SARS-CoV-2 spike protein interacts with human ACE2 receptors but not murine Ace2. Therefore, type-two diabetes was induced in humanized ACE2 (hACE2) transgenic knock-in mice using low-dose streptozotocin followed by eight weeks of a high-fat diet. Recombinant SARS-CoV-2 spike protein was injected intravenously in control and diabetic mice. Cognitive functions were tested using Y-maze and Barnes maze. Cerebral blood flow was measured using laser speckle imaging. RAAS system and TLR signaling were assessed using RT-PCR and western blot analysis. The cerebrovascular architecture was measured using immunohistochemistry. Human brain microvascular endothelial cells were treated with hyperglycemia (25 mM glucose) to mimic diabetic conditions.

Results: Spike protein exacerbated diabetes-induced cerebrovascular oxidative stress and inflammation as detected by increased (NOX1, NOX5) and (Il-6, Il-1β, and TNF-α) gene expression, respectively. Spike protein enhanced the destructive RAAS arm (angiotensin ll and AT1R) at the expense of the RAAS protective arm (ACE2 and AT2R) gene expression (P<0.05). In parallel, spike-protein exacerbated TLR signaling in diabetes as indicated by the increase in TLR-8 receptor and its ligands (HMGB1 and S100) and downstream adaptor proteins (MyD88, TRAF6, and NF-κB) expression (P<0.05). Spike-protein increased cerebrovascular rarefaction and decreased blood flow and cognitive functions in diabetes compared to control (P<0.05).

Conclusion: SAR-CoV-2 spike protein intensified RAAS and TLR signaling in diabetes, increasing cerebrovascular damage and cognitive dysfunction. Targeting RAAS and TLR singling are possible therapeutic strategies to protect against SAR-COV-2-induced cerebrovascular dysfunction in diabetes.