Lipoprotein lipase (LPL) is a hydrolytic enzyme which releases fatty acids and monoacylglyerol from nutrient-dependent triglyceride-rich lipoproteins [chylomicrons and very low density lipoproteins (VLDL)] and regulates the partitioning of these lipid fuels to tissues. This process has been studied most extensively in adipose tissue and muscle. However, LPL is also made in other sites including the nervous system, where the lipase is found in the brain, spinal cord and peripheral nerve. In the peripheral nerve, in vitro experiments have suggested, but not yet proven, that function of LPL is to enhance the uptake of chylomicron and VLDL triglyceride fatty acids to Schwann cells for myelin phospholipid synthesis. The studies outlined in this proposal will further this understanding by: 1) determining the sites of LPL expression within the peripheral nerve and defining the role of LPL in myelin synthesis nd peripheral nerve regeneration; 2) assessing the expression and regulation of peripheral nerve LPL in animal models of diabetic peripheral neuropathy; and 3) evaluating the efficacy of retro- and adenovirally mediated human LPL (hLPL) gene delivery to augment myelination following peripheral nerve injury, and reverse and/or retard the neuropathy of diabetes mellitus. A combination of experiments in rodents and cultured Schwann cells will be utilized. To more specifically determine the role of the LPL in peripheral nerve in rodents (Specific Aim #1), the cells of origin and response of LPL to crush injury will be examined in normal rats and mice, and in transgenic mice without LPL in the peripheral nerve.
In Specific Aim #2, several models of diabetic mellitus with already characterize peripheral neuropathy will determine if LPL expression in the peripheral nerve injury is impaired +/- crush injury. Finally, in Specific Aim #3, an important series of experiments will determine the efficacy of the delivery of LPL to augment myelination in regenerating nerves and in rodents with diabetic peripheral neuropathy. Two viral gene delivery systems will be evaluated for their ability to deliver hLPL to rat sciatic nerve: retrovirus-mediated gene delivery, which targets dividing cells, and adenovirus-mediated gene delivery, which introduces genes into non-dividing cells. The method that better facilitates sciatic nerve recovery from crush injury will then be administered to rodent models of diabetic neuropathy in an attempt to improve peripheral nerve myelination. Overall, these studies should provide a comprehensive understanding of the role of LPL in the peripheral nerve. Moreover, we are hopeful that new insights into the treatment of peripheral neuropathies will also ensue.
