Figure 7
From: Hibernating brown bears are protected against atherogenic dyslipidemia
Futile cycles and re-esterification of lipids in hibernating brown bears during winter. Lipids are released from the white adipose tissue (‘WAT’) and mobilized through the bloodstream for oxidation at peripheral tissues. The increased enzymatic activity of the cholesteryl ester transfer protein (‘CETP’) in the plasma allows hibernating bears to recycle cholesterol via exchanges of cholesteryl-esters (‘CE’) and triacylglycerols (‘TAG’) between lipoproteins. ‘CE’ is transferred from high-density lipoproteins (‘HDL’) to very low- (‘VLDL’), low- (‘LDL’), and intermediate-density lipoproteins (‘IDL’), which fuel peripheral tissues, e.g., skeletal muscle (‘Muscle’). Further, a reduced rate of cholesterol synthesis at peripheral tissues, along with a lower activity level of the lipoprotein-bound lecithin-cholesterol acyltransferase (‘LCAT’), lead to maintain constant cholesterol contents in HDL, while increasing HDL size and reducing numbers of HDL particles 2a (‘HDL2a’), 3a (‘HDL3a’), and 3c (‘HDL3c’), at the exception of HDL subunits 2b (‘HDL2b’) known to be cardioprotective that increases. Also, the pro-inflammatory and pro-oxidative properties of the blood is reduced in winter hibernating brown bears as indicated by lowered plasma levels of the oxysterol, 7-Ketocholesterol (‘7KC’), and the isoprostane, 11ß-Prostaglandin F2α (‘11ßPG’), both indexes for atherosclerosis and cardiovascular risks. Because of the unique fast of hibernating bears, excretion of excess cholesterol through bile acid is not possible, leading to increased level of total (‘CHT’) and free cholesterol (‘CHF’), CE, TAG and phospholipids (‘PL’) in plasma, but not of muscle CHT level which decreases. Along with these higher lipid fluxes, blood antiradical resistance (‘AR’) is increased, dampening and/or reducing oxidative damages linked to lipid auto-oxidation, e.g., MDA-protein adducts (‘MDA’) or protein-carbonyls (‘PC’), in plasma and peripheral tissues, including skeletal muscles. Arrows indicate the directions of the changes. Colors of the arrows represent different components concerned by the changes: red for the lipid categories, blue for enzymatic activities and lipoproteins, and green for the players involved in inflammatory and pro-oxidative processes. Created with https://biorender.com.
