Peripheral nerve ischemia: apolipoprotein E deficiency results in impaired functional recovery and reduction of associated intraneural angiogenic response.

Apolipoprotein E-knockout (apoE KO) mice have peripheral sensory nerve defects, reduced and delayed response to noxious thermal stimuli, abnormal morphology of unmyelinated fibers, and impaired blood-nerve and blood-brain barriers. In this study, we show that, compared to wild-type mice, peripheral nerves of apoE KO mice have impaired ability to respond to ischemia, as demonstrated by measurement of motor and sensory conduction velocity. In addition, mice lacking apoE exhibit a deficit of reinnervation of ischemic epidermis, evaluated by immunofluorescent staining for the pan-neuronal marker PGP 9.5. Also regional nerve blood flow, measured by laser Doppler, and intraneural angiogenesis after ischemia are significantly compromised in apoE-deficient mice. Finally, upregulation of the angiogenic cytokine vascular endothelial growth factor (VEGF), which physiologically occurs after ischemia in the peripheral nerve of wild-type mice, is severely impaired in apoE KO mice. Among the several neural defects that have already been described in mice lacking apoE, this is the first demonstration that functional recovery to ischemia is impaired in the peripheral nerves of these animals. This deficit is mirrored by the inability of upregulating VEGF and mounting an appropriate intraneural angiogenic response following injury. These findings provide new evidence of possible interdependent relationships between VEGF, angiogenesis, and nerve function and regeneration and may provide new important information on the role of apoE in the nervous system.