Sphingolipid and Fatty Acid Biology in Prediabetes and Neuropathy

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ABSTRACT Prediabetes – a condition that precedes type 2 diabetes – affects more than 80 million Americans. Peripheral neuropathy is a diabetic complication that results in a loss of sensation in the limbs due to peripheral nerve damage, and it can develop in both type 2 diabetic as well as prediabetic patients. Despite the prevalence and severity of peripheral neuropathy, there are currently no disease-modifying options. Novel therapeutic targets are therefore of critical importance for future treatments. Dyslipidemia is characterized by increased levels of saturated fatty acids in the plasma, resulting in altered levels of sphingolipids. Ceramides are one type of sphingolipid that are lipotoxic to neurons. Accumulation of saturated fatty acids leads to mitochondrial dysfunction, and cellular apoptosis and may play a central role in the development of peripheral neuropathy. However, monounsaturated fatty acids protect neurons from ceramide-mediated toxicity in vitro, likely via the formation of intracellular lipid droplets. Reversal of ceramide accumulation using monounsaturated fatty acid supplementation may therefore be an effective strategy for normalizing ceramide profiles and preventing peripheral neuropathy. We hypothesize that peripheral neuropathy in prediabetes is the result of toxic ceramide accumulation in neurons in vivo. We further hypothesize that supplementing prediabetic mice with monounsaturated fatty acids will enhance lipid droplet synthesis in neurons to prevent ceramide accumulation and subsequent neurotoxicity. We will test these hypotheses by: 1) determining the ceramide profile of prediabetic mice with neuropathy in both plasma and peripheral nerves, 2) evaluating the efficacy of monounsaturated fatty acid supplementation on ceramide accumulation in prediabetic mice during neuropathy, and 3) determining the mechanisms by which ceramides damage the peripheral nervous system as well as determining the mechanisms by which monounsaturated fatty acid ameliorate this damage. Together, these studies will demonstrate that dyslipidemia plays a central role in the development of peripheral neuropathy and provide an immediate therapeutic target for future treatments.