The link between hypoxia and cholesterol synthesis in circadian time

The importance of circadian alignment for human health remains a neglected area of research, despite increasing evidence that disruption of the internal clock associates with metabolism related syndromes, with significant co-morbidities to other pathologies. The proposed project will make an important contribution to filling this gap. We will address some of the current unmet needs in determining the role of circadian clock components in co-occuring Obstructive Sleep Apnea (OSA), characterized by hypoxia and disturbed sleep periods, and cholesterol-related dyslipidemia. To the best of our knowledge, we are the first to investigate whether hypoxia resulting from OSA affects the disruption of the circadian rhythm of endogenous cholesterol synthesis and thereby promotes dyslipidemia and related metabolic abnormalities. We aim to identify RNA molecules and cholesterol-related metabolites as diurnal biomarkers that link hypoxic conditions of OSA with dyslipidemia. OSA has a high prevalence in the general population, affecting up to 50% of males and about 25% of females. Our project is thus timely, addressing a real contemporary health issue. It proposes innovative, time-of-the-day dependent solutions to expose biochemical components that are sensitive to hypoxia in OSA, and may expose patients that are most at risk for cholesterol-related metabolic complications. We will exploit the multi-disciplinary expertise of our team, and external collaborators, and apply state-of-the-art experimentation, clinical work and computational analysis, to 1) to determine the diurnal (circadian) variation in expression of selected core clock genes and cholesterol-linked genes, proteins and metabolites, in blood samples from hypoxic patients with different grades of OSA; 2) identify how hypoxia (and hypoxia inducible factors, HIFs) affect diurnal cholesterol synthesis and cholesterol-related dyslipidemia, and 3) stratify OSA patients based on the severity of the disease using RNA molecules and cholesterol-related metabolites that respond to hypoxia at a particular circadian time. We will test the hypotheses that i) the diurnal (circadian) oscillation of RNA molecules and cholesterol-related metabolites that respond to hypoxia will be most altered in patients with severe OSA; ii) hypoxia affects the circadian oscillation of sterols which are metabolized by the oxygen-dependent monooxygenase CYP51A1, and iii) we can identify the time point with best separation of mild and severe OSA patient groups based on the transcriptomes and cholesterol-related metabolomes. We will apply our original cell models, that allow monitoring of the circadian rhythm in living cells, to unravel the effects of hypoxia and HIFs on the cells’ daily rhythms and to determine the downstream targets, focused on cholesterol. We will apply our previous expertise in cholesterol synthesis to investigate the circadian aspects of OSA and cholesterol-related dyslipidemia. We have underway a circadian study design, involving patients with OSA who have different grades of the disease with unknown metabolic consequences. To the best of our knowledge we are the first to investigate if the circadian (time-of-the-day-dependent) blood biomolecules in patients with OSA can also be applied to assess parameters and mechanisms of cholesterol-related dyslipidemia. The project will deliver novel basic knowledge, such as novel diurnal transcripts and metabolites of the blood linked to hypoxia in humans, novel clock and cholesterol–related genes that link hypoxia and dyslipidemia, and identify how hypoxia and HIFsmodulate the circadian rhythm in living cells. The project also has a significant translational value. It will deliver a small set of diurnal transcripts and cholesterol-related metabolites as biomarkers and the time of the day where the best stratification of OSA patient groups can be achieved.