Dottorato in MORFOGENESI E INGEGNERIA TISSUTALE

Titolo della tesi: The interplay between metabolic alterations and circadian clock

Organism physiological functions are controlled by an intricate set of peripheral molecular signals, synchronised by the central clock machinery located in the suprachiasmatic nucleus (SCN) of hypothalamus. It is well described that circadian rhythmicity is fundamental for metabolic homeostasis; indeed, the arcuate nucleus (ARC) of hypothalamus, which is the primary regulator of organism energy balance, is strictly connected with SCN, to adjust metabolic functions in response to circadian variations. Moreover, peripheral tissues are controlled by peripheral clock genes according to central-to-peripheral hierarchy; tissue clock genes participate to the modulation of metabolism genes expression, and are in turn regulated by metabolites levels. The general aim of the PhD project was to deeply investigate the interplay between metabolism and circadian clock in three physio-pathological contexts, namely Amyotrophic Lateral Sclerosis (ALS), obesity, and aging. Interestingly, these three conditions share metabolic and hypothalamic dysfunctions, along with other common pathological hallmarks. Indeed, in the development of ALS, obesity and aging a primary role is played by defects in metabolism, in the biogenesis of mitochondria, and by the impairment of autophagic processes, which in all produce high levels of oxidative stress. The activation of immune system represents another common feature of ALS, obesity, and aging; in particular, aberrant immune response has been defined as one of the causes of ALS pathogenesis; moreover, high levels of oxidative stress associated to obesity and aging result in an increased production of pro-inflammatory cytokines, that finally activate a chronic low-grade inflammation. ALS, obesity, and aging are characterised by alterations in the physiology of different tissues and organs including skeletal muscle, which is severely compromised in these conditions. Indeed, tissue metabolism has been found altered in presence of ALS, obesity, and aging; furthermore, in the analysed pathological conditions skeletal muscle is severely affected by atrophy. Therefore, the aim of this project was to better characterise and compare the pathological alterations in ALS, obesity, and aged mouse models, particularly in terms of metabolic disfunctions and their interplay with central and peripheral clock. Moreover, in previous studies of our laboratory the role of the Insulin-like Growth Factor 1 (IGF-1) has been investigated, demonstrating that muscle restricted over-expression of IGF-1 can attenuate ALS disease progression and counteract atrophy in aged muscles; here we investigated the role of IGF-1 in the modulation of metabolism in relation to circadian clock, in the three pathological conditions. We observed that ALS, obesity and aging are characterised by systemic and muscular metabolic dysfunctions, together with alterations of core clock genes expression, in both skeletal muscle and hypothalamic central clock. Interestingly, IGF-1 over-expression exerts a positive role on muscle-nerve interplay and on skeletal muscle homeostasis, partially rescuing circadian rhythm alterations; moreover, we demonstrated that muscle restricted over-expression of IGF-1 retrogradely influence hypothalamic nuclei responsible for circadian and metabolic homeostasis. Overall, these data demonstrate the crucial role of skeletal muscle on the regulation of systemic metabolism and circadian rhythmicity.