The role of Annexin-A1 in the pathophysiology of diabetes.

Abstract

Diabetes is a complex disease characterised by hyperglycaemia, which often leads to microvascular complications including diabetic nephropathy and cardiomyopathy. In this thesis, I have investigated the role of Annexin-A1 (ANXA1), an endogenous anti-inflammatory peptide, in two experimental murine models of diabetes caused by streptozotocin (STZ) or high-fat high-sugar diet (HFD), which mimic type-1 (T1DM) and type-2 diabetes (T2DM) respectively. I have also investigated the levels of ANXA1 in patients with either T1DM or T2DM. Patients with T1DM have increased plasma ANXA1 levels. In a murine models of type 1 diabetes loss of endogenous ANXA1 aggravates both cardiac and renal dysfunction in mice. Specifically, I have shown that key mediators of the MAPK pathway (p38, JNK and ERK1/2) are constitutively activated in ANXA1-/- mice, and activation of these pathways is exacerbated in diabetic ANXA1-/- mice. Administration of human recombinant (hr) ANXA1 did not alter the diabetic phenotype in diabetic WT mice, but attenuated the cardiac and renal dysfunction caused by STZ. Interestingly, late administration of ANXA1 (after significant cardiac and renal dysfunction had already developed) halted the progression of both cardiac and renal dysfunction. Patients with T2DM have increased plasma ANXA1 levels. HFD-fed ANXA1-/- mice have a more severe diabetic phenotype compared to HFD-fed WT mice. Therapeutic administration of hrANXA1 prevented the development of a diabetic phenotype. Specifically, I have shown that the insulin signalling pathway is further perturbed in diabetic mice resulting in severe insulin resistance, and that these signalling abnormalities were prevented by therapeutic administration of hrANXA1. In addition, loss of endogenous ANXA1 aggravates both cardiac and renal dysfunction in mice with experimental T2DM. The GTPase RhoA is constituently activated in ANXA1-/- mice leading downstream activation of MYPT1. Feeding a HFD also activated the small GTPase RhoA, leading to increased MYPT1 activity, which could be attenuated with treatment with hrANXA1. Mice subjected to HFD for 12 weeks had a more ‘leaky’ blood brain barrier (BBB), which is further exacerbated in ANXA1-/- mice fed a HFD. Compared to mice fed a chow diet, mice fed a HFD had an augmented CD4+ T-cell profile; with a clear decline in CD4+FoxP3+ (anti-inflammatory) and increase in CD4+RORgt+ (pro-inflammatory) cells. Administration of hrANXA1 to mice fed on HFD restored BBB integrity and CD4+ T-cells profile similar to mice fed on normal chow diet. Mice fed a HFD also had more activated CD4+ T-cells, which adhered more readily and transmigrated through a brain endothelial mono-layer ex vivo. In contrast, administration of hrANXA1 to mice fed on HFD reduced re-activity of CD4+ T-cells, reducing the number of adherent CD4+ T-cells to the brain endothelial mono-layer.