BTBD9, a novel regulator of manganese-induced neurotoxicity

Project Summary: Manganese (Mn) is an essential metal, but excess exposure is associated with increased risk for Parkinson's disease (PD). Restless legs syndrome (RLS) is a common neurological disorder seen in ~10% of the US population. The pathobiology of RLS has been linked to deficits in dopaminergic (DAergic) function and Fe deficiency. Interestingly, increased prevalence of PD is noted in RLS, and vice versa. BTBD9 is one of the genetic risk factors for RLS. Fe-deficiency is associated with increased brain deposition of Mn, and Mn shares numerous homeostatic and transport pathways with Fe, suggesting that concentrations of another metal, such as Mn, may opportunistically increase upon Fe deficiency. Given the established link between Fe and Mn biology, we propose to evaluate whether BTBD9 may regulate Mn-induced cytotoxicity and DAergic neurodegeneration. Furthermore, in vivo evidence has linked insulin/insulin-like growth factor (IGF) signaling with both Mn biology and RLS. Mn-deficiency caused glucose intolerance and reduced insulin production, while Mn toxicity caused reduced ATP and insulin/IGF receptor expression. Meanwhile, patients with diabetes have significantly increased risk to develop RLS than non-diabetic groups. These observations support links between (1) Mn neurotoxicity, (2) DA neurobiology/ parkinsonism, (3) RLS, and (4) IGF signaling. However, we lack a mechanistic basis for the direct targets of Mn neurotoxicity in IGF signaling networks and the role DA neurobiology plays in these mechanisms. Here, we propose a direct protein target (BTBD9) regulating IGF signaling to protect against oxidative stress and mitochondrial dysfunction induced by Mn exposure, thus protecting DAergic function. We will use the Caenorhabditis elegans (C. elegans) model as it shares a highly conserved neurogenetic architecture and IGF signaling components with mammalians. Our preliminary data established the requisite technology and conceptual basis for this proposal. Our hypothesis will be tested in the following Specific Aims:!Specific Aim 1. Investigate the protective mechanism of BTBD9/HPO-9 against Mn-induced toxicity and its role in IGF signaling in C. elegans. We will verify whether HPO-9 moderates oxidative stress, mitochondrial mass, membrane potential, ATP production and how it regulates the IGF signaling upon Mn exposure. Specific Aim 2. Determine if HPO-9 modulates Mn-induced DAergic neurotoxicity via IGF signaling in C. elegans. We will assess DAergic neurodegeneration, DA-dependent behavior and DA concentrations in worms upon Mn exposure. Results from this study will have a broad clinical and translational impact. Our scientific approach will (1) reveal if systemic and/or neuronal alterations in Mn may contribute to the impaired DAergic function seen in RLS (2) establish a functional link between Mn biology, DAergic functionality and IGF signaling 3) provide a new target protein for therapeutic interventions to ameliorate oxidative stress and mitochondrial dysfunction, a process inherent to multiple neurodegenerative disorders. !