The role of nuclear non-coding RNA Giot1 in salt and water intake throughout the life-course.
Over the past decade, it has become clear that mammalian genomes encode thousands of long non-coding RNAs (lncRNAs). Many long lncRNAs act in the nucleus to regulate gene expression, but their physiological functions remain to be determined. We aim to decipher the mechanisms whereby brain nuclear lncRNA Giot1 controls salt palatability and consumption. The precise regulation water balance is essential for survival and good health and wellbeing, and when threatened, osmotic stability is aggressively defended. However, these mechanisms go wrong in old age, and diminished thirst and salt-appetite can result in disorders of fluid balance that are a frequent cause of morbidity and mortality in the elderly. Integrated neuroendocrine and behavioural mechanisms function to control the excretion and consumption of water and salt in order to maintain the optimal bodily composition required for good health. Given a choice, rats would rather consume 0.9% w/v NaCl over water (appetite), but would rather consume water over 2% w/v NaCl (aversion). However, aversion is overcome if 2% w/v NaCl is the only fluid source (salt loading for up to 7 days, SL); the salty solution is avidly consumed. At the same time, integrative hypothalamic structures (the paraventricular nucleus, PVN, and the supraoptic nucleus, SON) activate the secretion of the antidiuretic neuropeptide hormone arginine vasopressin (VP) from magnocellular neuron (MCN) axon terminals in the posterior pituitary (PP), which acts on the kidney to provoke water conservation. We have identified a nuclear lncRNA called Giot1 that is robustly up-regulated in the PVN and SON by SL. We have shown that: *Giot1 activates salt drinking in SL animals. *Giot1 regulates the expression of the gene encoding the endogenous opioid peptide dynorphin (Dyn). *Blockade of Dyn kappa-opioid receptors (KORs) at the level of the amygdala (Amyg) can inhibit salt intake during SL. *Expression of Giot1 increases in the PVN and SON with old age in rats. We suggest that VP MCNs paradigmatic for the novel concept that neuroendocrine neurons can be involved in the simultaneous dual regulation of homeostasis and allostasis. In response to life-threatening physiological cues, these neurones respond by regulating both PP hormone secretion (homeostatic) and neuronal neurotransmitter secretion (allostatic regulation of preference). In the context of their role in allostasis, we hypothesise that lncRNA Giot1 regulates the expression of neurotransmitters that enable salt ingestion, through projections to limbic areas under different physiological conditions. We further hypothesise that these mechanisms alter in old age. To robustly challenge these hypotheses, we are now characterising the Giot1 RNA at the molecular level, and are investigate the physiological and behavioural roles of Giot1. Our aims are to: *determine which structures in the nucleus contain Giot1 RNA. *ask whether the Giot1 RNA is trapped in the nucleus, or whether it shuttles between nucleus and cytoplasm. *elucidate the Giot1 lncRNA interactome, and determine how it regulates gene expression. *map the projections of Giot1-expressing MCNs. *investigate the involvement of Giot1, Dyn and KOR in salt palatability. *ask whether Giot1 has a role in salt hunger. *determine the physiological and behavioural roles of specific MCN-limbic connections. *ask about the role of Giot1 in disturbances of salt homeostasis in old age.