Abstract- Project 3: The role of AgRP/Augα-ALK pathway in FGF21’s brain action on aging During the past 5 years, we have shown that systemic adaptation to calorie restriction is hinging on appropriate hypothalamic circuit activity and integrity. We specifically observed that these parameters impacted by FGF21 are critically regulated by hypothalamic AgRP neurons, which themselves are under the control of FGF21. FGF21 induces activation of these hypothalamic neurons, which results in altered functional connectivity of hypothalamic circuits in support of behavior and autonomic regulation. In line with the involvement with FGF21’s action, our preliminary studies demonstrated that impaired AgRP circuit integrity shortens mean lifespan of male mice when fed ad-libitum. Strikingly, however, shorter lifespan of AgRP-impaired animals showed significantly lower disease burden, including dramatic lower incidence of neoplastic events in these animals. In pursuit of this paradoxical outcome, we have investigated mechanisms that are innate to AgRP neurons with relevance to cancer development. In collaboration between the labs of the PIs (Tamas Horvath and Joseph Schlessinger), we unmasked a previously unsuspected cancer-related cellular signaling modality between AgRP neurons and cells in the paraventricular nucleus in control of systemic energy and glucose metabolism. We found that AgRP neurons metabolic state-dependently express Augmentor α (Augα), a recently discovered ligand of the receptor tyrosine kinase, ALK. ALK is expressed in the hypothalamic paraventricular nucleus, and, we found these cells to be innervated by AgRP fibers originating in the arcuate nucleus. Knock down of Augα resulted in thinness, which replicated the phenotype of ALK knockout animals. Our preliminary single cell RNAseq studies also identified that the AgRP/Augα-ALK pathways is parallel but not overlapping in the PVN with that of AgRP-MC4R pathway. Thus, we identified a novel signaling modality downstream of FGF21, which employs AgRP neurons and a pathway (Augα-ALK) shown to be co-opted in etiology of multiple cancers. These observations gave impetus to the central hypothesis of this project, which is that the Augα-ALK pathways originating in the hypothalamic AgRP neurons impacts systemic action of FGF21, and, that this pathway is involved in AgRP circuit integrity-dependent propagation of cancer development and lifespan. The following Specific Aims will test these hypotheses: Specific Aim 1 will determine whether Augα obstructs calorie restriction and FGF21-induced behavioral- and peripheral tissue adaptations mediated by AgRP neurons. Specific Aim 2 will assess the role of AgRP/Augα-ALK signaling pathway in in the effect of calorie restriction and FGF21 on hippocampal and cortical circuit integrity. Specific Aim 3 will interrogate the role of AgRP/Augα-ALK signaling pathway in lifespan in ad libitum fed, calorie restricted and/or FGF21 treated mice. The execution of these studie...