Introduction Insulin resistant disorders, such as diabetes, are associated with impaired angiogenesis. Using mice haploinsufficient for the insulin receptor (IRKO), versus wild-type (WT) littermate controls, it is possible to define the impact of systemic resistance on vascular biology, independent of hyperglycaemia.
Methods Developmental retinal angiogenesis was defined in P5 mice. Pathological angiogenesis was studied in adult mice after induction of hind-limb ischaemia; limb perfusion was assessed 21 days later using laser Doppler and gastrocnemius muscle capillary density defined histologically. VEGF-induced angiogenesis was assessed in vitro using an aortic sprouting assay and a Matrigel lung endothelial cell tubulogenesis assay. Data are expressed as mean[SEM]; p < 0.05 is denoted by *.
Results IRKO exhibited reduced vascular branching complexity (1048  versus 1199  branches/mm2*), tip cell formation (18.3 [0.2] versus 21.1 [0.3] tip cells/mm), and NG2+ pericyte coverage (51.6 [0.9] versus 59.8 [1.4]% of endothelial cell area*) in the developing retina. Adult IRKO also demonstrated impaired recovery of limb perfusion (0.62 [0.07] versus 0.82 [0.06] ischaemic/non-ischaemic flux ratio*), associated with reduced capillary density (42.1 [4.3] versus 57.9 [3.3] capillaries/microscopic field*). qRT-PCR revealed a 3.2-fold greater* expression of VEGF-A in the ischaemic muscle of IRKO. Endothelial sprouts from the aortae of IRKO were less abundant (21.8 [2.4] versus 29.9 [2.2] sprouts*), and were shorter (847  versus 1037  µm*). IRKO endothelial cells produced fewer tubules in response to VEGF-A (14.3 [2.4] versus 27.5 [2.9] tubules/microscopic field*).
Conclusion Insulin resistance, without dysglycaemia, is associated with abnormal developmental and pathological angiogenesis, and impaired functional response to the pro-angiogenic growth factor VEGF-A. Further studies are required to define the mechanism.
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