An In Vivo Investigation into the Actions of the Hypothalamic Neuropeptide, QRFP

Abstract

Pyroglutamylated RFamide peptide (QRFP) is a peptide expressed at highest levels in the mediobasal hypothalamus, with lower levels of expression found in several tissues in the periphery. QRFP acts through a G-protein coupled receptor (Gpr103) of which, uniquely in rodents, there are two isoforms. Administration of exogenous QRFP induces feeding in satiated rodents, along with acute increases in locomotor activity and energy expenditure. Furthermore, a number of effects have been observed on tissues in vitro. It is currently unclear which of these actions may translate into a physiological function of QRFP. This thesis, therefore, aimed to elucidate the physiologically relevant functions of QRFP, through the use of new transgenic mouse lines, with studies being guided by results from the administration of exogenous QRFP.By central injection of QRFP, we confirmed a number of in vivo responses: increased food intake, increased locomotor activity, increased energy expenditure and alterations in the handling of glucose. Our observations guided further study of these endpoints in our FlEx-Qrfp mouse (a Qrfp knock-out line), and two further lines lacking either of the Gpr103 receptor isoforms. Data from these receptor knock-out lines suggest some redundancy in the system, although expression of both receptors appears to be required for full QRFP-induced responses.Following our observations that exogenous QRFP induced locomotor activity, irrespective of time of administration, we have begun to investigate the potential role of QRFP in the sleep/wake cycle. FlEx-Qrfp knock-out mice are hypoactive, particularly during the dark phase of the light cycle, providing evidence for an important role for QRFP here, similar to that observed with another hypothalamic neuropeptide, orexin. Subsequently we have conducted neuronal mapping studies, using a Qrfp-cre model. QRFP neurons are located in the mediobasal hypothalamus, surrounding the ventromedial hypothalamic nucleus. The more lateral distributed cells intermingle with orexin-containing neurons. We show that QRFP neurons project to regions associated with the control of arousal, such as the locus coeruleus, dorsal raphé nucleus, tuberomammillary nucleus and ventral tegmental area. Retrograde tracing was used to confirm the locus coeruleus connection.Our FlEx-Qrfp knock-out mouse had no obvious metabolic phenotype when maintained on chow diet, but gained less weight when fed a high-energy diet. This was reflected by a lower fat mass in the adipose tissue of knock-out mice, coupled with lower fat storage in the liver. This body-weight phenotype was not caused by decreased feeding, or increased locomotor activity, thermogenesis or energy expenditure. FlEx-Qrfp knock-out mice showed an increased expression of lipolytic genes in white adipose tissue and liver. We have also shown that central administration of QRFP alters glucose handling, causing a blunting of the initial peak in glucose excursion following oral glucose loading. We propose that these two actions may be linked and we hypothesise that QRFP neurons may normally inhibit sympathetic output from the brain, thereby reducing sympathetic drive to tissues such as the pancreas and adipose tissue.

Date of Award	1 Aug 2017
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Simon Luckman (Supervisor) & Reinmar Hager (Supervisor)