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Research Projects
Dr Chen Chen MD, PhD
Head of Endocrine Cell Biology Group
Senior Research Fellow (NH&MRC)
Honorary Senior Lecturer in Physiology, Monash University
Phone 9594 4371
E-mail: chen.chen@princehenrys.org
Dr Damien Keating PhD
The TM Ramsay Fellow
Phone 9594 4380
E-mail: damien.keating@princehenrys.org
The Endocrine Cell Biology focuses on the regulation of endocrine cells, which secret hormones important in controlling growth, development, metabolic balance, body mass composition, ageing process, and the plasma glucose levels. Several endogenous and synthetic regulatory peptides have been tested for their regulatory roles in pituitary and pancreatic hormones. The long-term goal of these researches is to find a way to therapeutically correct growth hormone (GH) and insulin deficiency. In addition, possible paracrine or autocrine effect of a newly discovered hormone, Ghrelin, in the regulation of uterine endometrium tissue remodelling process, is under the investigation in collaboration with Uterine Biology group. We also collaborate with Breast Cancer group to investigate the effect of oestrogen (E2) on the development of growth hormone cells in pituitary glands. A number of research projects are available.
Projects available:
1. Physiological roles of newly identified hormone, ghrelin, on pituitary somatotropes
Supervisor: Dr Chen Chen & Dr Ming Yan
GH secretion is mainly regulated by GH-releasing hormone (GHRH) and somatostatin (SRIF) from hypothalamus. Newly identified hormone, ghrelin, also stimulates GH secretion through a specific receptor (GHS-R). Physiological or pathological roles of ghrelin or synthetic analog, GHRP, are not clear. We found that long-term action of GHRP on pituitary GH secreting cells (somatotropes) enhanced GHRH-induced GH secretion. Such an action of GHRP may reflect physiological action of ghrelin and is vitally important for clinical use of the synthetic GHRP to treat GH deficiency. The mechanism for this priming effect of GHRP and ghrelin is not clear and our current focus is on the regulation of GH, GHRH receptor (GHRH-R) and GHS-R, SRIF-R, and Pit-1 expression levels in pituitary somatotropes using quantitative molecular biology methods. Protein levels of hormone and receptors will also be studied.
2. Membrane ion channels and signalling systems in the regulation of hormone secretion
Supervisor: Dr Chen Chen & Dr Damien Keating
Hormone secretion depends on the intracellular free Ca2+ concentration ([Ca2+]i), which is regulated by releasing or inhibitory regulators of endocrine cells. The change in [Ca2+]i is achieved by altering the activities of membrane ion channels, intracellular signalling systems, as well as the release of Ca2+ from intracellular Ca2+ storage sites. Those events are investigated in this laboratory by measuring single living cell [Ca2+]i using fluorometrical and laser confocal microscopic methods, ion channel activity by patch clamp methods, and exocytosis by membrane capacitance and fluorescent microscopic measurements. The signalling systems in the cell are studied by intracellular dialysis and antisense transfection methods. This study aims to clarify the physiological roles of ion channels and signal events in the basic cell biology of endocrine cells.
3. The mechanism of pancreatic -cell dysfunction in type-2 diabetes
Supervisor: Dr Chen Chen & Dr Damien Keating
Type-2 diabetes is caused by peripheral tissue insulin resistance and -cell dysfunction. The latter occurs before the diagnostic criteria are met for diabetes. Numerous evidences indicate a link between diabetes and obesity. This project focuses on the interaction between adipocytes and -cells in vitro and aims to find adipocyte-derived factors responsible for -cell dysfunction. With co-culture system established in our lab, we confirmed the -cell dysfunction by differentiated adipocytes. We also identified several possible factors from adipocytes influencing -cell function in terms of key molecular expression in the cell, [Ca2+]i response to glucose and insulin secretion. We are now looking for the molecular mechanism of -cell dysfunction by adipocyte-derived factor and in the process of converging our search for responsible factors leading to the way to prevent the -cell dysfunction.
4. Role of oestrogen in the development of pituitary somatotropes
Supervisors: Dr Chen Chen, Dr Ming Yan, Dr Margaret Jones & Professor Evan Simpson
It has been reported that oestrogen regulates the basal and GHRH-stimulated GH secretion, in female oestrogen stimulates and in male reduces GH releases. The mechanism for such a regulation is not clear and results are controversial. Technical difficulties in accurately controlling long-term oestrogen levels are the major reason for the obscures in this area. We recently found that GH, GHS-R and GHRH-R mRNA levels were down-regulated in ArKO mice, where CYP19 gene coding the aromatase was knocked out. As aromatase catalyses the final step in the biosynthesis of estrogens from C19 steroids, ArKO mouse is a mouse model of oestrogen-deficiency. We would like to extend this research by including several age groups to study the role of oestrogen in the development of GH axis. The effect of oestrogen replacement will also be investigated. After confirming expression, hormone and receptor protein levels will also be evaluated by hormone and receptor binding and western blot assays.
5. Functional development of pituitary endocrine cells
Supervisor: Dr Chen Chen
There are two releasing hormones identified to regulate GH, GHRH and a recent identified Ghrelin (or endogenous GH secretagogues, GHS). The obvious question is why we need both releasing hormones to stimulate GH secretion. A high ghrelin (or GHS) receptor expression was found in early age and pituitary tumours and significantly declined in adulthood. We want to extend our knowledge in this area by experimenting on pituitary glands from different age groups of rat and sheep using well-established molecular biology methods in our laboratory. This will be fundamental to understand physiological and pathological roles of GHRH and Ghrelin.
6. Mechanism for GH deficiency in obesity
Supervisor: Dr Chen Chen, Dr Ming Yan
Our previous experiments demonstrated that in vitro treatment of pituitary cells with adipocyte-released leptin reduced GH secretion in response to GHRH stimulation. We also found that orexin, an appetitive hormone from hypothalamus, increases the Ca2+ current in GH secreting somatotropes. We want to clarify the mechanism underlying the modification of GH secretion by leptin and orexin treatment. Using molecular biology technique to analyse the expression of GH, GHS-R and GHRH-R, we will get information at the transcription level. We will also use receptor-binding and western blot techniques to analyse GHS-R and GHRH-R levels in somatotropes. Single cell signalling and ion channels will also be investigated after treatment to demonstrate a change of cell biology function underlying the regulation by leptin and orexin. Interrelationship between leptin/orexin and GHS/GHRH will also be studied.
7. Distribution of Ghrelin and Ghrelin receptor in human endometrium tissue
Supervisor: Dr Chen Chen & Dr Lois Salamonsen
Since the recent discovery of Ghrelin and its receptor-GHS-R, the Ghrelin-GHS-R system has been linked to a number of functions including the regulation of GH, appetite, adipocytes differentiation, energy expenditure, and tumour development. The distribution of Ghrelin and GHS-R in peripheral tissues is an urgent question to answer and generates extensive research efforts. We have established RT-PCR methods to identify Ghrelin and GHS-R mRNA from total RNA samples and immunocyto-chemical staining of Ghrelin and GHS-R using specific antibodies. In our preliminary experiments, we found both Ghrelin and GHS-R in uterine endometrium tissue and the levels of expression were tightly in correlation to menstrual cycle and the malignancy of the endometrium tumours. The intention of this project is to clarify the changing pattern of the receptor and Ghrelin in this tissue and the role of this system in endometrium physiology and pathology.
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