Figure 3. Age and disease dependent cholesterol loading into mouse lung.

(A–B) Cholesterol measured per mg of lung tissue (A) and per μg of total proteins in the lung (B) in 8-week-old (wo), 28wo mice. An aged diabetic mouse, generated by diet induced obesity (DIO), loaded ~45% more cholesterol into its lung tissue per μg of total proteins. Expressed as mean ± s.e.m., *P<0.05, **P<0.01, one-way ANOVA. (C) Association of ACE2 with GM1 clusters determined by dSTORM pair correlation in mouse lung tissue. (D) Cholesterol is taken up into the lung tissue of mice fed a high fat diet. (E) Representative dSTORM images from (C). Cholesterol (yellow shading) was loaded into the lung of mice (left) and fixed and removed and the tissue directly imaged. Scale bar, 500 nm. (F) Proposed model for SARS-CoV-2 infection of lung tissue of obese patients. In young, cholesterol is low, there are few entry points, and ACE2 is ill positioned with PIP₂ domains (not shown) away from GM1 clusters (dark grey, entry points). With age, average cholesterol levels in the tissue increases. In obese/diabetic patients, tissue cholesterol levels are the highest and ACE2 receptor is positioned in GM1 clusters for optimal viral entry (PIP₂ domains not shown).