Pro-Calcific Environment Impairs Ischaemia-Driven Angiogenesis.

Peripheral arterial disease (PAD) is characterised by accelerated arterial calcification and impairment in angiogenesis. Studies implicate vascular calcification as a contributor to PAD, but the mechanisms remain unclear. We aimed to determine the effect of calcification on ischaemia-driven angiogenesis. Human coronary artery endothelial cells (ECs) were treated with calcification medium (CM: CaCl2 2.7 mM, Na2PO4 2.0 mM) for 24 h and exposed to normoxia (5% CO2) or hypoxia (1.2% O2; 5% CO2 balanced with N2). In normoxia, CM significantly inhibited tubule formation and migration and upregulated calcification markers of ALP, BMP2, and Runx2. CM elevated levels of calcification-protective gene OPG, demonstrating a compensatory mechanism by ECs. CM failed to induce pro-angiogenic regulators VEGFA and HIF-1α in hypoxia and further suppressed the phosphorylation of endothelial nitric oxide synthase (eNOS) that is essential for vascular function. In vivo, osteoprotegerin-deficient mice (OPG-/-), a calcification model, were subjected to hind-limb ischaemia (HLI) surgery. OPG-/- mice displayed elevated serum alkaline phosphatase (ALP) activity compared to wild-type controls. OPG-/- mice experienced striking reductions in blood-flow reperfusion in both 8-week-old and 6-month-old mice post-HLI. This coincided with significant impairment in tissue ischaemia and reduced limb function as assessed by clinical scoring (Tarlov). This study demonstrated for the first time that a pro-calcific environment is detrimental to ischaemia-driven angiogenesis. The degree of calcification in patients with PAD can often be a limiting factor with the use of standard therapies. These highly novel findings require further studies for full elucidation of the mechanisms involved and have implications for the development of therapies to suppress calcification in PAD.

Circadian disruption by short light exposure and a high energy diet impairs glucose tolerance and increases cardiac fibrosis in Psammomys obesus.

Type 2 diabetes mellitus (T2DM) increases cardiac inflammation which promotes the development of cardiac fibrosis. We sought to determine the impact of circadian disruption on the induction of hyperglycaemia, inflammation and cardiac fibrosis. METHODS: Psammomys obesus (P. obesus) were exposed to neutral (12 h light:12 h dark) or short (5 h light:19 h dark) photoperiods and fed a low energy (LE) or high energy (HE) diet for 8 or 20 weeks. To determine daily rhythmicity, P. obesus were euthanised at 2, 8, 14, and 20 h after 'lights on'. RESULTS: P. obesus exposed to a short photoperiod for 8 and 20 weeks had impaired glucose tolerance following oral glucose tolerance testing, compared to a neutral photoperiod exposure. This occurred with both LE and HE diets but was more pronounced with the HE diet. Short photoperiod exposure also increased myocardial perivascular fibrosis after 20 weeks on LE (51%, P < 0.05) and HE (44%, P < 0.05) diets, when compared to groups with neutral photoperiod exposure. Short photoperiod exposure caused elevations in mRNA levels of hypertrophy gene Nppa (atrial natriuretic peptide) and hypertrophy transcription factors Gata4 and Mef2c in myocardial tissue after 8 weeks. CONCLUSION: Exposure to a short photoperiod causes impaired glucose tolerance in P. obesus that is exacerbated with HE diet and is accompanied by an induction in myocardial perivascular fibrosis.