Adam Gesing

Metabolic effects of intra-abdominal fat in GHRKO mice

Mice with targeted deletion of the growth hormone receptor (GHRKO mice) are growth hormone (GH) resistant, small, obese, hypoinsulinemic, highly insulin sensitive and remarkably long‐lived. To elucidate the unexpected coexistence of adiposity with improved insulin sensitivity and extended longevity, we examined effects of surgical removal of visceral (epididymal and perinephric) fat on metabolic traits related to insulin signaling and longevity. Comparison of results obtained in GHRKO mice and in normal animals from the same strain revealed disparate effects of visceral fat removal (VFR) on insulin and glucose tolerance, adiponectin levels, accumulation of ectopic fat, phosphorylation of insulin signaling intermediates, body temperature, and respiratory quotient (RQ). Overall, VFR produced the expected improvements in insulin sensitivity and reduced body temperature and RQ in normal mice and had opposite effects in GHRKO mice. Some of the examined parameters were altered by VFR in opposite directions in GHRKO and normal mice, and others were affected in only one genotype or exhibited significant genotype × treatment interactions. Functional differences between visceral fat of GHRKO and normal mice were confirmed by measurements of adipokine secretion, lipolysis, and expression of genes related to fat metabolism. We conclude that in the absence of GH signaling, the secretory activity of visceral fat is profoundly altered and unexpectedly promotes enhanced insulin sensitivity. The apparent beneficial effects of visceral fat in GHRKO mice may also explain why reducing adiposity by calorie restriction fails to improve insulin signaling or further extend longevity in these animals.

The thyroid gland and the process of aging; what is new?

The endocrine system and particular endocrine organs, including the thyroid, undergo important functional changes during aging. The prevalence of thyroid disorders increases with age and numerous morphological and physiological changes of the thyroid gland during the process of aging are well-known. It is to be stressed that the clinical course of thyroid diseases in the elderly differs essentially from that observed in younger individuals, because symptoms are more subtle and are often attributed to normal aging. Subclinical hypo- and hyperthyroidism, as well as thyroid neoplasms, require special attention in elderly subjects. Intriguingly, decreased thyroid function, as well as thyrotropin (TSH) levels – progressively shifting to higher values with age – may contribute to the increased lifespan.This short review focuses on recent findings concerning the alterations in thyroid function during aging, including these which may potentially lead to extended longevity, both in humans and animals.

Expression of Key Regulators of Mitochondrial Biogenesis in Growth Hormone Receptor Knockout (GHRKO) Mice is Enhanced but is Not Further Improved by Other Potential Life-Extending Interventions

Mitochondrial biogenesis is essential for cell viability. Growth hormone receptor knockout (GHRKO), calorie restriction, and surgical visceral fat removal constitute experimental interventions to delay aging and increase life span. We examined the expression of known regulators of mitochondriogenesis: peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α), adenosine monophosphate (AMP)-activated protein kinase (AMPK), sirtuin-1 (SIRT-1) and sirtuin-3 (SIRT-3), endothelial nitric oxide synthase (eNOS), nuclear respiratory factor-1, mitochondrial transcription factor A (TFAM), and mitofusin-2 (MFN-2) in the skeletal muscles and hearts of control and calorie-restricted female GHRKO mice and in the kidneys of male GHRKOs after visceral fat removal or sham surgery. Expression of PGC-1α in skeletal muscles, AMPK, SIRT-1, SIRT-3, eNOS, and MFN-2 in the heart and PGC-1α, AMPK, SIRT-3, eNOS, and MFN-2 in kidneys was increased in GHRKO mice but was not affected by calorie restriction or visceral fat removal. GHRKO mice have increased expression of key regulators of mitochondriogenesis, which is not improved further by calorie restriction or visceral fat removal.

The contribution of visceral fat to improved insulin signaling in Ames dwarf mice.

Ames dwarf (Prop1df, df/df) mice are characterized by growth hormone (GH), prolactin, and thyrotropin deficiency, remarkable extension of longevity and increased insulin sensitivity with low levels of fasting insulin and glucose. Plasma levels of anti‐inflammatory adiponectin are increased in df/df mice, while pro‐inflammatory IL‐6 is decreased in plasma and epididymal fat. This represents an important shift in the balance between pro‐ and anti‐inflammatory adipokines in adipose tissue, which was not exposed to GH signals during development or adult life. To determine the role of adipose tissue in the control of insulin signaling in these long‐living mutants, we examined the effects of surgical removal of visceral (epididymal and perinephric) adipose tissue. Comparison of the results obtained in df/df mice and their normal (N) siblings indicated different effects of visceral fat removal (VFR) on insulin sensitivity and glucose tolerance. The analysis of the expression of genes related to insulin signaling indicated that VFR improved insulin action in skeletal muscle in N mice. Interestingly, this surgical intervention did not improve insulin signaling in df/df mice skeletal muscle but caused suppression of the signal in subcutaneous fat. We conclude that altered profile of adipokines secreted by visceral fat of Ames dwarf mice may act as a key contributor to increased insulin sensitivity and extended longevity of these animals.

Growth hormone abolishes beneficial effects of calorie restriction in long-lived Ames dwarf mice.

Disruption of the growth hormone (GH) axis promotes longevity and delays aging. In contrast, GH over-expression may lead to accelerated aging and shorter life. Calorie restriction (CR) improves insulin sensitivity and may extend lifespan. Long-lived Ames dwarf (df/df) mice have additional extension of longevity when subjected to 30% CR. The aim of the study was to assess effects of CR or GH replacement therapy separately and as a combined (CR+GH) treatment in GH-deficient df/df and normal mice, on selected metabolic parameters (e.g., insulin, glucose, cholesterol), insulin signaling components (e.g., insulin receptor [IR] β-subunit, phosphorylated form of IR [IR pY1158], protein kinase C ζ/λ [p-PKCζ/λ] and mTOR [p-mTOR]), transcription factor p-CREB, and components of the mitogen-activated protein kinase (MAPK) signaling (p-ERK1/2, p-p38), responsible for cell proliferation, differentiation and survival. CR decreased plasma levels of insulin, glucose, cholesterol and leptin, and increased hepatic IR β-subunit and IR pY1158 levels as well as IR, IRS-1 and GLUT-2 gene expression compared to ad libitum feeding, showing a significant beneficial diet intervention effect. Moreover, hepatic protein levels of p-PKCζ/λ, p-mTOR and p-p38 decreased, and p-CREB increased in CR mice. On the contrary, GH increased levels of glucose, cholesterol and leptin in plasma, and p-mTOR or p-p38 in livers, and decreased plasma adiponectin and hepatic IR β-subunit compared to saline treatment. There were no GH effects on adiponectin in N mice. Moreover, GH replacement therapy did not affect IR, IRS-1 and GLUT-2 gene expression. GH treatment abolishes the beneficial effects of CR; it may suggest an important role of GH-IGF1 axis in mediating the CR action. Suppressed somatotrophic signaling seems to predominate over GH replacement therapy in the context of the examined parameters and signaling pathways.

TSH receptor antibodies have predictive value for breast cancer – retrospective analysis

BackgroundAssociations between breast cancer and thyroid disorders are reported in numerous studies. Relationships between thyroperoxidase antibodies (TPOAb), thyroglobulin antibodies (TgAb) and breast cancer have been previously demonstrated. However, no analysis has been performed concerning an association between thyrotropin (TSH) receptor antibodies (TSHRAb) and breast cancer. The aim of the study was to evaluate the prevalence of breast cancer or benign breast tumors in patients with Graves’ disease and to analyze a possible relationship between Graves’ disease and these two groups of breast diseases with emphasis to epidemiology and laboratory findings.Patients and methodsClinical and laboratory details of 2003 women hospitalized for endocrine disorders were retrospectively analyzed, using an unpaired Student’s t-test, logistic regression analysis, χ2 test of independence or the two-sided ratio comparison test.ResultsThe coexistence of Graves’ disease and breast cancer was statistically significant. We observed TSHRAb and TgAb more frequently in patients with breast cancer. We found that TSHRAb is the only variable possessing predictive value for breast cancer.ConclusionsThe strong relationship between Graves’ disease and breast cancer is proposed. We suggest that TSHRAb could be described as a positive determinant of breast cancer. The present data call attention to the usefulness of screening for breast cancer in long-term follow-up of patients with autoimmune thyroid disorders, especially of those with Graves’ disease. Similarly, screening for autoimmune thyroid disorders should be performed in patients with nodular breast disease. Additionally, the article draws ideas for further research in order to develop targeted treatment for more successful outcome in patients with breast cancer.

The thyroid gland and the process of aging

The endocrine organs, including the thyroid gland, undergo important functional changes during aging. It is known that the prevalence of thyroid disorders increases with age. Importantly, subclinical disturbances of thyroid function are more frequent than overt diseases in the elderly. Moreover, the clinical course of thyroid diseases in elderly people differs from that observed in younger subjects; namely, symptoms are more subtle and are often attributed to normal aging, and therefore, require special attention in elderly individuals. One of the subclinical thyroid function disturbances is subclinical hypothyroidism, which is characterized by normal free thyroxine (FT4) and increased thyrotropin (TSH) levels. The prevalence of subclinical hypothyroidism increases with aging and ranges from 3 to 16 % in individuals aged 60 years and older [1]. In contrast to overt hypothyroidism, the subclinical hypothyroidism in elderly subjects is not associated with impairment of physical and cognitive function, depression, metabolic disturbances or poor quality of life [2,3]. Subclinical hypothyroidism is also not associated with the increased overall mortality risk [2]. Moreover, there is not association between subclinical hypothyroidism and incident coronary heart disease (CHD), heart failure (HF) or cardiovascular (CV) mortality [4]. Similarly, total mortality was not increased in subjects with subclinical hypothyroidism, although the risk of CHD events and of CHD mortality increased with TSH levels 10 mU/L or higher [5]. Importantly, a quite high rate of reversion of subclinical hypothyroidism to euthyroidism in individuals aged at least 65 years with lower baseline TSH levels (4.5-6.9 mU/L) and antithyroid peroxidase antibody (TPOAb) negativity (≤ 37 IU/L) was observed [6]. In turn, higher TSH levels and TPOAb positivity were independently associated with lower chance of reversion to euthyroid status; TSH levels ≥10 mU/L were independently associated with progression to overt hypothyroidism [6]. There are obvious indications for overt hypothyroidism treatment. In turn, indications for treatment of subclinical hypothyroidism are still quite controversial. Nevertheless, the replacement therapy with L-thyroxine is not uniformly recommended in elderly people with subclinical hypothyroidism. For example, L-thyroxine replacement therapy did not improve cognitive function in elderly individuals with subclinical hypothyroidism [7]. Moreover, despite improvement of lipid profile due to treatment of L-thyroxine in subclinical hypothyroidism, there is no clear evidence that this beneficial effect can be associated with decreased cardiovascular or all-cause mortality in elderly patients [8]. Intriguingly, thyroid hypofunction, as well as elevated thyrotropin (TSH) levels may contribute to the extended lifespan. A potential contribution of TSH and thyroid hormones to lifespan regulation was observed in the studies performed on thyroid disease-free population of Ashkenazi Jews, characterized by exceptional longevity (centenarians). For example, the higher serum TSH level in these individuals in comparison with the control groups was observed [9]. Thus, increased serum TSH level seems to be associated with extreme longevity [9]. Moreover, two single nucleotide polymorphisms (SNPs) in TSH receptor (TSHR) gene (namely rs10149689 and rs12050077) were associated with increased TSH level in Ashkenazi Jewish centenarians and their offspring [10]. Also, an inverse correlation between FT4 and TSH levels in centenarians was reported [9] which may suggest a potential role of decreased thyroid function in lifespan regulation, leading to extended longevity. The findings obtained in the Leiden Longevity Study actually show the associations between low thyroid activity and exceptional familial longevity [11]. Also in animals, a reduced thyroid function with low levels of T4 seems to be associated with extended longevity [12-14]. A very severe thyroid hypofunction was observed in Ames dwarf (df/df) mice. These animals are characterized by mutations at the Prop-1 (Prophet of pituitary factor 1) gene and demonstrate a lack of growth hormone (GH), prolactin and TSH. These features may unexpectedly contribute to remarkable longevity in Ames dwarf mice [12]. Furthermore, severe hypothyroid Ames dwarfs and mice with targeted disruption of the growth hormone (GH) receptor/GH binding protein gene (GH receptor knockout; GHRKO) with mild thyroid hypofunction, have decreased thyroid follicle size which may explain decreased thyroid hormone levels in these long-lived mutants [15]. In conclusion, the altered thyroid function may play, via different mechanisms [16], a relevant role in lifespan regulation. Namely, decreased thyroid function may lead to extended longevity.

Transcriptome profiling reveals divergent expression shifts in brown and white adipose tissue from long-lived GHRKO mice

Mice lacking the growth hormone receptor (GHRKO) exhibit improved lifespan and healthspan due to loss of growth hormone signaling. Both the distribution and activity of brown and white adipose tissue (BAT and WAT) are altered in GHRKO mice, but the contribution of each tissue to age-related phenotypes has remained unclear. We therefore used whole-genome microarrays to evaluate transcriptional differences in BAT and WAT depots between GHRKO and normal littermates at six months of age. Our findings reveal a unique BAT transcriptome as well as distinctive responses of BAT to Ghr ablation. BAT from GHRKO mice exhibited elevated expression of genes associated with mitochondria and metabolism, along with reduced expression of genes expressed by monocyte-derived cells (dendritic cells [DC] and macrophages). Largely the opposite was observed in WAT, with increased expression of DC-expressed genes and reduced expression of genes associated with metabolism, cellular respiration and the mitochondrial inner envelope. These findings demonstrate divergent response patterns of BAT and WAT to loss of GH signaling in GHRKO mice. These patterns suggest both BAT and WAT contribute in different ways to phenotypes in GHRKO mice, with Ghr ablation blunting inflammation in BAT as well as cellular metabolism and mitochondrial biogenesis in WAT.

The role of transplanted visceral fat from the long-lived growth hormone receptor knockout mice on insulin signaling

Growth hormone receptor knockout mice (GHRKO) are characterized by high insulin sensitivity and extended lifespan. Interestingly, the secretory activity of visceral fat in GHRKO mice is altered, stimulating whole body insulin sensitivity. In this study, we transplanted normal (N) mice with visceral fat pads from GHRKO or N mice to determine the role of visceral fat on the insulin signaling. We found that the transplant of visceral fat from GHRKO mice to N mice (N-GHRKO) improved whole body insulin sensitivity when comparing with sham-operated mice (N-S) and with mice that received visceral fat from N mice (N-N). This was associated with increased hepatic insulin sensitivity as observed by the increased phosphorylated insulin receptor and increased hepatic expression of Pparα and Pparγ. In conclusion, we demonstrated that visceral fat transplant from GHRKO mice into normal mice enhanced insulin sensitivity and glucose tolerance. These results further confirm the differential physiological role played by visceral adipose tissue from GH receptor deficient mice, indicating that the increase of this fat depot can be associated with beneficial effects on insulin signaling and longevity.

Key regulators of mitochondrial biogenesis are increased in kidneys of growth hormone receptor knockout (GHRKO) mice

The growth hormone receptor knockout (GHRKO) mice are remarkably long‐lived and highly insulin sensitive. Alterations in mitochondrial biogenesis are associated with aging and various metabolic derangements. We have previously demonstrated increased gene expression of key regulators of mitochondriogenesis in kidneys, hearts and skeletal muscles of GHRKO mice. The aim of the present study was to quantify the protein levels of the following regulators of mitochondriogenesis: peroxisome proliferator‐activated receptor γ co‐activator 1α (PGC‐1α), AMP‐activated protein kinase α (AMPKα), phospho‐AMPKα (p‐AMPKα), sirtuin‐3 (SIRT‐3), endothelial nitric oxide synthase (eNOS), phospho‐eNOS (p‐eNOS), nuclear respiratory factor‐1 (NRF‐1) and mitofusin‐2 (MFN‐2) in skeletal muscles and kidneys of GHRKOs in comparison to normal mice. We also were interested in the effects of calorie restriction (CR) and visceral fat removal (VFR) on these parameters. Both CR and VFR improve insulin sensitivity and can extend life span. Results: The renal levels of PGC‐1α, AMPKα, p‐AMPKα, SIRT‐3, eNOS, p‐eNOS and MFN‐2 were increased in GHRKOs. In the GHRKO skeletal muscles, only MFN‐2 was increased. Levels of the examined proteins were not affected by CR (except for PGC‐1α and p‐eNOS in skeletal muscles) or VFR. Conclusion: GHRKO mice have increased renal protein levels of key regulators of mitochondriogenesis, and this may contribute to increased longevity of these knockouts. Copyright