Painful Versus Insensate Diabetic Neuropathy

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Project Summary Patients with prediabetes and diabetes are at an elevated risk for diabetic peripheral neuropathy (DPN). DPN primarily affects the distal limbs and is associated with pain, loss of sensation, gait abnormalities and reduced quality of life. This renewal will focus on a dietary intervention using a ketogenic diet (KD) to prevent and reverse symptoms of DPN. Consumption of a KD results in elevated ketone bodies, with beta- hydroxybutyrate (bOHB) and acetoacetate as key mediators. Generated by the liver, ketone bodies can be used directly by non-hepatic cells, such as neurons, as an alternative fuel source to glucose or in a signaling capacity. Axon degeneration in DPN, particularly small fibers, leads to reduced epidermal innervation for which there are currently no clinical treatments. The metabolic and energetic status of sensory axons contributes to axon loss, and the addition of ketone bodies as a fuel source could be an important modulator of cellular energy and metabolic function. Pain is a major contributor to decreased quality of life in patients with DPN, which is compromised by a lack of effective clinical treatments. Our overall hypothesis is that ketone bodies improve features of DPN through actions directly on sensory neurons. We will test our hypothesis using dietary interventions in mouse models of prediabetes and diabetes, as well as incorporate a Cre-lox mouse model lacking the ability to utilize ketone bodies in sensory neurons (advCre-SCOT-/- mice) to determine whether direct effects of ketones on peripheral sensory neurons drive these beneficial effects. Aim 1 will test whether ketone bodies act directly on sensory neurons to stimulate axon growth in DPN. Experiments will include both in vitro and in vivo assessment of axon growth as a result of a KD, and explore cellular signaling pathways involved in axon guidance, energy signaling pathways, and mitochondrial function. Aim 2 will test whether ketone bodies reduce pain (mechanical allodynia) in DPN by scavenging MGO. Experiments will incorporate ex vivo electrophysiology to identify response and firing properties of identified sensory neurons in settings of MGO and a KD. Additional experiments will test whether a KD has similar anti-nociceptive action in a chemotherapy- induced neuropathy model where changes in metabolism do not play a role. Results from these studies will fill an important gap in DPN research by providing new information about how a KD can improve neuronal metabolism and stimulate axon growth. These results will identify interventions that could be developed for pain control in DPN, including new mechanisms related to MGO toxicity.