Research in Molecular Mechanisms of Aging
By: Xiaowei Xu
Ph.D.in Pharmacology, May 1996
Pharmacology, Bowmam Gray school of Medicine.
Effects of Aging and Moderate Caloric Restriction On Growth Hormone Receptor Signal Transduction
Following is the abstract of Xu's dissertation :
Biological aging is closely associated with a decline in the capacity for protein synthesis which has been hypothesized to contribute to the decline in tissue function and increased susceptibility to disease. Growth hormone and IGF-1 are two important anabolic hormones that regulate metabolic processes including protein synthesis in almost all tissues throughout the lifespan of mammals. Previous studies indicate that age-related perturbations in the neuroendocrine lead to a loss of growth hormone pulse amplitude and a subsequent decline in plasma IGF-1 concentration. However, despite an increase in growth hormone receptor (GHR) density with age, growth hormone induced plasma IGF-1 levels remain low in aged animals, suggesting that tissue resistance to growth hormone may be an additional manifestation of age. Moderate caloric restriction is one of the few regimens consistently reported to decrease the appearance of age-related pathologies, and increase mean and maximum lifespan. This regimen increases protein synthesis, enhances growth hormone secretion and prevents the age-related decline in IGF-1. The studies in this project were designed to: 1) determine whether alterations in tissue responsiveness to growth hormone contributes to the age-related decrease in plasma IGF-1 and protein synthesis 2) assess the precise mechanisms responsible for increased tissue resistance to growth hormone with age and 3) determine whether tissue resistance to growth hormone with age can be altered by moderate caloric restriction.
The first study examined the relationship between age-related alterations in GHR density, growth hormone induced IGF-1 gene expression, GHR and JAK2 kinase phosphorylation, and the basal expression and activity of cytosolic MAP kinase in liver from female C57BL/6 mice. The results of this study demonstrated that growth hormone induces phosphorylation of JAK2 kinase and GHR, increases cytosolic MAP kinase activity and IGF-1 gene expression. Despite a two fold increase in GHR density in old ad libitum animals, there was a marked decline in IGF-1 gene expression that was associated with a reduction in JAK2 kinase and GHR phosphorylation. These data suggest that the signal transduction pathway for growth hormone is impaired with age and that these deficits contribute to the decline in IGF-1 gene expression.
The second study assessed the effects of long term moderate caloric restriction on age-related changes in tissue responsiveness to growth hormone. Old caloric restricted animals demonstrated a significant increase in GHR, JAK2 kinase phosphorylation and MAP kinase activity in response to growth hormone stimulation compare to old ad libitum fed animals as well as growth hormone induced 3H-leucine incorporation, IGF-1 gene expression and secretion in female C57BL/6 mice. The results of this study indicated that moderate caloric restriction prevents the age-related decline in GHR signal transduction, suggesting that the effects of moderate caloric restriction are mediated, at least in part, by improve tissue sensitivity to growth hormone.
The spatial separation between the site of signal initiation and the nuclear targets of signal transduction indicates that information must be transferred between different subcellular compartments. Studies indicate that several intracellular proteins are phosphorylated in response to growth hormone, including STATs protein and MAP kinase, which then move into the nucleus and promote gene transcription. The results of activation of the GHR either through STATs or MAP kinase is an increase in IGF-1 gene expression and secretion. The third study examined Stat3 and MAP kinase nuclear translocation after growth hormone stimulation in ad libitum and moderate caloric restricted B6D2 male mice of different ages. Although growth hormone induced nuclear MAP kinase translocation did not change with age in ad libitum animals, growth hormone induced nuclear translocation of Stat3 decreased significantly, suggesting that the JAK2 kinase-Stat3 pathway is specifically impaired with age. The age-related decline in growth hormone induced nuclear Stat3 translocation was not evident in caloric restricted animals and 36 months old caloric restricted mice had a two fold greater growth hormone induced nuclear Stat3 than 36 month old ad libitum animals. In addition, caloric restricted animals exhibited an age-related increase in basal JAK2 kinase levels, suggesting that increased JAK2 levels may be part of the compensatory mechanisms that serve to maintain GHR signal transduction and IGF-1 gene expression in these animals.
We conclude that tissue responsiveness to growth hormone decreases with age and contributes to the decline in plasma IGF-1 levels. The mechanisms responsible for this age-related deficiency appear to be related to diminished capacity of growth hormone to phosphorylate JAK2 kinase resulting in a decline in Stat3 phosphorylation and translocation into nucleus. In addition, the effects of aging are reversed by moderate caloric restriction possibly by increased in JAK2 kinase levels and activities. Our results indicate that increased growth hormone resistance is an important manifestation of aging which contributes to the decline in tissue protein synthesis and function. Moderate caloric restriction appears to prevent or delay age associated declines in tissue function by maintaining the capacity for adequate receptor signal transduction.
The Use of the Human Growth Hormone in the Elderly
By: Dr. Steve Novil
To talk about HGH it is nessesary to talk briefly about the pituitary gland, which is the gland that produces the HGH. This gland is divided in three parts and with a very notable structure. Each part produces different hormones, and these hormones will stimulate specific parts in the body. We know that HGH stimulates the growth in children, but what effects can we expect in the adult?
Which anti-aging effects can it give us?
The HGH or SOMATOTROPIN is produced in the front pituitary and this hormone stimulates not only growth in the body, it works also in the proteins, electrolytes, and carbohydrates metabolism, soluble colagen synthesis and erithropoyesis. It's effect on growth is not direct, it works through the somatomedines or growth factors(sulfatation factors), also sinergistically with other glands in the body.
All adults are interested in finding one substance that can give us better quality of life, one substance that:
- Has an anabolic effect
- Reenforces the immune system
- Burns the fat
- Repairs the tissue damage
- Repairs the muscle and increases the strength and mass
AIDS Patients On Growth Hormone Gain Weight Without Eating More
VANCOUVER, Canada, July 8, 1996 -- Patients with HIV-associated wasting who received daily injections of human growth hormone gained weight, particularly lean body mass, without consuming significantly more calories, according to the results of a University of California San Francisco study presented here today.
The 12 patients in the study, who were all treated at the UCSF-affiliated San Francisco General Hospital, gained an average of four pounds over a three-month period without any significant increases in intake of overall calories, protein, fat or carbohydrates, the researchers reported.
"I think all of us were a little surprised by the results. Weight gain rarely occurs without a gain in caloric intake," said Viva Tai, R.D., M.P.H., a UCSF research dietitian who presented the study results. "It's remarkable that you can gain this much body mass without eating significantly more calories."
The patients -- 11 men and one woman -- gained an average of nearly eight pounds in lean body mass but lost an average of four pounds of fat, Tai said. It appears that the growth hormone was able to tap into existing fat stores in the body to build muscle, she said.
"It may be possible that the loss in fat fuels the energy required for the synthesis and maintenance of lean body mass," she said.
The results were based on food diaries in which patients recorded everything they ate during the week before they started the study and the week before their three-month follow-up visit. Over the three-month period, the patients' daily intake increased by 194 calories from 2,647 to 2,841 average total calories per day, the researchers calculated.
Those 194 additional calories could not account for the weight gain as studies have shown that AIDS patients on growth hormone burn an average of 230 extra calories a day even while at rest, Tai said. She said the results are important because they suggest that growth hormone "may work for people who have an appetite problem and can't eat 3,000 calories a day."
Building lean body mass is particularly important as this is the tissue that enables people to function and be mobile, she said.
"I can tell you from working with these patients over three years that how they walked in and how they are living their lives now are totally different. They have a different outlook on life. They are more independent. Some of these patients have had important improvements in quality of life," she said.
Tai's colleagues in the study are Morris Schambelan, M.D., UCSF professor of medicine, and Kathleen Mulligan, Ph.D., UCSF assistant professor of medicine.
The Cause of Aging
North Dakota State University Experiment
Longevity Report 33, page 4. By Douglas Skrecky
Recently the cause of aging has been discovered by medical researchers. It has turned out to be quite simple. In an experiment at North Dakota State University 19 month old aged mice were given injection of either growth hormone or saline twice a week. After 13 weeks of treatment 39% of the saline mice were still alive. This is normal. Of the growth hormone treated mice 93% were still alive after 13 weeks. This is not normal at all. The injections were then stopped for 6 weeks. During this period all of the remaining saline treated mice died of old age while only 1 out of 20 mice that had received growth hormone expired. The researchers then reinstituted growth hormone injections in the remaining 19 animals for a further 6 weeks. At the end of the experiment 18 mice were still alive. And so with little fanfare the major cause of age associated mortality was discovered. Experiments with aged humans have confirmed that the administration of growth hormone brings about signs of rejuvenation such as reduction of adipose tissue, a
What Researchers have to say about Human Growth Hormone
Daniel Rudman, M.D., New England Journal of Medicine:
"The effects of six months of human growth hormone on lean body mass and adipose-tissue were equivalent in magnitude to the changes incurred during 10-20 years of aging."
V.A. Medical Center and Department of Medicine, Stanford University Medical Center:
Concludes: "It is possible that chronic physiologic GH and/or IGF-I replacement therapy might reverse (or prevent) some of these "inevitable" sequelae of aging". (Study of GH therapy in the elderly - March 1992.)
Dr. Jorgensen and Dr. Christian of Copenhagen, Denmark, in European Journal of Endocrinology, 1994:
"Replacement therapy with Growth Hormone has shown beneficial/normalizing effect on parameters such as cardiac and renal function, thyroid hormone metabolism, bone metabolism, sweat secretion, total and regional fuel metabolism and psychological well being"
Dr. Anthony Karpos, M.D.:
"We really have something here which may be able to reverse some of the problems associated with aging."
Drs. Ramias, Shamos, and Schiller of St. Joseph Hospital Medical Center in Phoenix, AZ:
The Doctors found HGH to be a potent anabolic agent "Daily Administration of human growth hormone in the first week after trauma would enhance the metabolic status.... resulting in reduced morbidity and earlier discharge from hospital." (May 1992, Journal of Surgery. Vol 111, 495-502.)
Dr. Jake Powrie, M.D. and Dr. Andrew Weissberger, St. Thomas Hospital, London, England:
"All adults with growth hormone deficiency should now be considered for growth hormone replacement therapy." (1995)
Dr. Rosen, M.D. and Dr. G. Johannsson, M.D. of University Hospital, Goteborg, Sweden:
"There is no evidence suggestion that Growth Hormone Replacement Therapy causes any unfavorable long term side effects." (Hormone Research, 1995)
References:
1. Salomon F, Cuneo RC, Hesp R et al. The Effects of Treatment with Recombinant Human Growth Hormone on Body Composition and Metabolism in Adults with Growth Hormone Deficiency. New England Journal of Medicine 1989;321:1797-1803.
2. Bengtsson BA. The Consequences of Growth Hormone Deficiency in Adults. Acta Endocrinologica 1993;128 (Suppl 2):2-5.
3. Cuneo RC, Salomon F, Wiles CM et al. Growth Hormone Treatment in Growth Hormone Deficient Adults. II. Effects on Exercise Performance. Journal of Applied Physiology 1991;70:695-700.
4. O'Halloran DJ, Tsatsoulis A, Whitehouse RW et al. Increased Bone Density after Recombinant Human Growth Hormone (GH) Therapy in Adults with Isolated GH Deficiency. Journal of Clinical Endocrinology and Metabolism 1993;76:1344-1348.
5. McGauley GA, Cuneo RC, Salomon F et al. Psychological Well-Being Before and After Growth Hormone Treatment in Adults with Growth Hormone Deficiency. Hormone Research 1990;33 (suppl 4):52-54.
6. Bengtsson BA, Eden S, Lonn L et al. Treatment of Adults with Growth Hormone (GH) Deficiency with Recombinant Human GH. Journal of Clinical Endocrinology and Metabolism 1993;76;309-317.
7. Johnston DG, Bengtsson BA. Workshop Report: the Effects of Growth Hormone and Growth Hormone Deficiency on Lipids and the Cardiovascular System. Acta Endocrinologica 1993;128 (Suppl 2): 69-70.
8. Amato G, Carella C, Fazio S et al. Body Composition, Bone Metabolism, and Heart Structure and Function in Growth Hormone (GH)-Deficient Adults Before and After GH Replacement Therapy at Low Doses. Journal of Clinical Endocrinology and Metabolism 1993;77:1671-1676.
9. Standford University Medical Center (Psycho-Neuro Endocrinology, VOl. 17, no. 4, 1992 __ many effects of aging can now be reversed, bring about dramatic rejuvenating results in older people:
From The Illinois Acadamy Of Sciences School of Medicine Databases Endocrinology Databases
Plasma Insulin-Like Growth Factor-1 and Insulin-like Growth Factor-2 In Women During Aging (±sem)
DECADE
IGF-1
ng/mlIGF-2
ng/ml30's
240 ± 58
723 ± 217
40's
198 ± 5
711 ± 255
50's
194 ± 58
891 ± 193
60's
150 ± 54
718 ± 230
70's
172 ± 72
776 ± 234
80's
144 ± 54
644 ± 136
s well as increases in growth hormone-insulin-like growth factor 1, muscle mass, bone density and skin thickness. The major project left in the field of aging is to discover why growth hormone secretion is suppressed with increasing age.
Growth hormone and Insulin-ike Growth Factor-I
DEPARTMENT OF PHYSIOLOGY GÖTEBORG UNIVERSITY DISSERATIONS (Ph.D. Thesis): Abstract
Vikman-Adolfsson, K.
Growth hormone and insulin-like growth factor-I in the regulation of lipoprotein lipase in the rat.
Growth hormone has profound effects on lipid metabolism. Both body fat mass and lipoprotein metabolism are regulated by Growth Hormone. Lipoprotein lipase (LPL) is a key enzyme of triglyceride removal from the circulation and hence supply adipose as well as muscle tissues with fatty acids for storage or as an energy fuel. In the present study, the regulation of Growth Hormone receptors (GHR) and the Growth Hormone dependent growth factor, insulin-like growth factor-I (IGF-I) expression by Growth Hormone in adipose tissue of hypophysectomized rats was investigated. Moreover, the effects of Growth Hormone and IGF-I in the regulation of LPL activity in adipose tissue and muscle tissues were studied in order to get further insight into the mechanisms by which Growth Hormone and IGF-I regulate body fat and lipoprotein metabolism. Hypophysectomized rats were used. They were given hydrocortisone acetate and L-thyroxine as replacement therapy. In addition, human or bovine recombinant Growth Hormone or human recombinant IGF-I were given by subcutaneous injections or as a continuous subcutaneous infusion using osmotic minipumps. After 5-7 days of treatment, the rats were killed and the tissues excised. Messenger ribonucleic acid levels in the selected tissues (GHR, IGF-I and LPL) were quantified by a solution hybridization technique. Lipase activity was measured using assays in which radiolabeled triacylglycerol is hydrolyzed and labeled free fatty acids measured. IGF-I, insulin, glucose and free fatty acid concentrations were quantified using standard methods. Glucose incorporation into lipids in adipose tissue explants or isolated adipocytes as well as into glycogen in the soleus muscle were studied in vitro. Hypophysectomy resulted in decreased GHR mRNA levels in adipose tissue of hypophysectomized rats. After a single injection of Growth Hormone, GHR mRNA was induced within two hours. A Growth Hormone dose-dependent increase in GHR mRNA levels was found. Northern blot analysis revealed two transcriptsof 3.6 kb and of 1.2 kb, which are believed to encode the full length Growth Hormone receptor and a Growth Hormone binding protein, respectively. IGF-I mRNA levels decreased in adipose tissue following hypophysectomy. Growth Hormone treatment dose-dependently increased IGF-I mRNA levels. In vitro, addition of Growth Hormone to isolated adipocytes increased IGF-I mRNA and the accumulation of IGF-I into the medium. Post-heparin plasma lipoprotein lipase and hepatic lipase (HL) activities decreased after hypophysectomy of female rats. In these experiments, Growth Hormone was given either as two daily s.c injections or as a continuous s.c infusion. Irrespective of the mode of administration, LPL and HL activities increased by Growth Hormone treatment. In adipose tissue, LPL activity was unchanged after hypophysectomy, but was increased by Growth Hormone treatment. LPL mRNA levels changed in parallel. In the heart and the gastrocnemius muscle, hypophysectomy resulted in decreased LPL activity and Growth Hormone administration increased LPL activity. In the heart LPL activity changed in parallel with LPL mRNA levels, whereas no effect of Growth Hormone treatment on LPL mRNA levels was found in the gastrocnemius muscle. Finally, the effect of IGF-I treatment on LPL activity was studied. In adipose tissue, IGF-I treatment of hypophysectomized rats reduced LPL activity. No effect of IGF-I treatment on LPL activity in the heart or gastrocnemius muscle was observed. Insulin stimulated glucose incorporation into lipids was reduced in adipose tissue. In the soleus muscle, glycogen content and insulin stimulated glycogen synthesis increased after IGF-I treatment. In summary, Growth Hormone interacts and regulates its own receptor in adipose tissue. This interaction results in increased expression and production of IGF-I. Growth Hormone increases both LPL and hepatic lipase activities, effects that may be of importance in the regulation of lipoprotein turn-over by Growth Hormone. IGF-I does not stimulate LPL activities, indicating that the effect of Growth Hormone on lipoprotein turn-over may not be mediated via IGF-I. On the the other hand, IGF-I inhibited basal and insulin stimulated lipogenesis in adipose tissue and increased glycogen storage in skeletal muscle.