Lucila Sackmann-Sala

Endocrine Parameters and Phenotypes of the Growth Hormone Receptor Gene Disrupted (GHR−/−) Mouse

Disruption of the GH receptor (GHR) gene eliminates GH-induced intracellular signaling and, thus, its biological actions. Therefore, the GHR gene disrupted mouse (GHR-/-) has been and is a valuable tool for helping to define various parameters of GH physiology. Since its creation in 1995, this mouse strain has been used by our laboratory and others for numerous studies ranging from growth to aging. Some of the most notable discoveries are their extreme insulin sensitivity in the presence of obesity. Also, the animals have an extended lifespan, which has generated a large number of investigations into the roles of GH and IGF-I in the aging process. This review summarizes the many results derived from the GHR-/- mice. We have attempted to present the findings in the context of current knowledge regarding GH action and, where applicable, to discuss how these mice compare to GH insensitivity syndrome in humans.

Growth hormone and adipose tissue: beyond the adipocyte

The last two decades have seen resurgence in research focused on adipose tissue. In part, the enhanced interest stems from an alarming increase in obesity rates worldwide. However, an understanding that this once simple tissue is significantly more intricate and interactive than previously realized has fostered additional attention. While few would argue that growth hormone (GH) radically alters fat mass, newer findings revealing the complexity of adipose tissue requires that GHs influence on this tissue be reexamined. Therefore, the objective of this review is to describe the more recent understanding of adipose tissue and to summarize our current knowledge of how GH may influence and contribute to these newer complexities of this tissue with special focus on the available data from mice with altered GH action.

Activation of the GH/IGF-1 axis by CJC-1295, a long-acting GHRH analog, results in serum protein profile changes in normal adult subjects

OBJECTIVE To identify biomarkers of growth hormone (GH) and insulin-like growth factor 1 (IGF-1) action in human serum. BACKGROUND The search for new markers of GH activity has received extensive attention given that the current biomarkers (IGF-1, IGFBP-3 and collagen peptides) show substantial variability in the population, and are not reliably predictive of either the physiologic effects of GH therapy or the detection of GH abuse by athletes. GH releasing hormone (GHRH) is a polypeptide synthesized in the hypothalamus that binds to receptors on pituitary somatotropes to promote the synthesis and release of GH. Serum GH and IGF-1 levels have been shown to increase with administration of GHRH or CJC-1295, a long-acting GHRH analog. DESIGN Sera from 11 healthy young adult men before and one week after CJC-1295 injection were analyzed by two-dimensional gel electrophoresis for proteomic changes. Serum proteins displaying significant changes before and after treatment were subsequently identified using mass spectrometry. In addition, correlations between these proteins and GH or IGF-1 levels were evaluated. RESULTS Two protein spots that displayed decreased intensities after treatment were identified as an apolipoprotein A1 isoform and a transthyretin isoform. Three protein spots upregulated by CJC-1295 treatment included beta-hemoglobin, a C-terminal fragment of albumin, and a mix of an immunoglobulin fragment and another C-terminal albumin fragment. A linear relationship was found between the spot containing immunoglobulin and albumin fragments and IGF-1 levels. CONCLUSIONS Although the molecular mechanisms linking the identified proteins to GH and IGF-1 biological activity remain to be clarified, the results suggest that they represent potential biomarkers of GH and/or IGF-1 action.

The use of proteomics to study infectious diseases.

Technology surrounding genomics, or the study of an organisms genome and its gene use, has advanced rapidly resulting in an abundance of readily available genomic data. Although genomics is extremely valuable, proteins are ultimately responsible for controlling most aspects of cellular function. The field of proteomics, or the study of the full array of proteins produced by an organism, has become the premier arena for the identification and characterization of proteins. Yet the task of characterizing a proteomic profile is more complex, in part because many unique proteins can be produced by the same gene product and because proteins have more diverse chemical structures making sequencing and identification more difficult. Proteomic profiles of a particular organism, tissue or cell are influenced by a variety of environmental stimuli, including those brought on by infectious disease. The intent of this review is to highlight applications of proteomics used in the study of pathogenesis, etiology and pathology of infectious disorders. While many infectious agents have been the target of proteomic studies, this review will focus on those infectious diseases which rank among the highest in worldwide mortalities, such as HIV/AIDS, tuberculosis, malaria, measles, and hepatitis.

Novel serum biomarkers for erythropoietin use in humans: a proteomic approach

Erythropoietin (Epo) is produced primarily in the kidneys upon low blood oxygen availability and stimulates erythropoiesis in the bone marrow. Recombinant human Epo (rHuEpo), a drug developed to increase arterial oxygen content in patients, is also illicitly used by athletes to improve their endurance performance. Therefore, a robust and sensitive test to detect its abuse is needed. The aim of the present study was to investigate potential human serum biomarkers of Epo abuse employing a proteomic approach. Eight healthy male subjects were injected subcutaneously with rHuEpo (5,000 IU) every second day for a 16-day period. Serum was collected before starting the treatment regime and again at days 8 and 16 during the treatment period. Samples were homogenized and proteins separated by two-dimensional gel electrophoresis (2DE). Spots that changed significantly in response to rHuEpo treatment were identified by mass spectrometry. Both the number of reticulocytes and erythrocytes increased throughout the study, leading to a significant increase in hematocrit and hemoglobin content. In addition, transferrin levels increased but the percentage of iron bound to transferrin and ferritin levels decreased. Out of 97 serum proteins, seven were found to decrease significantly at day 16 compared with pre-Epo administration, and were identified as four isoforms of haptoglobin, two isoforms of transferrin, and a mixture of hemopexin and albumin. In support, total serum haptoglobin levels were found to be significantly decreased at both days 8 and 16. Thus a 2DE proteomic approach for discovery of novel markers of Epo action appears feasible.

Serum proteome changes in acromegalic patients following transsphenoidal surgery: novel biomarkers of disease activity

CONTEXT Transsphenoidal adenomectomy is the primary treatment for acromegaly. However, assessment of the therapeutical outcome remains problematic since the existing biomarkers of disease activity frequently show discordant results. OBJECTIVE To discover novel serum biomarkers of disease activity in acromegalic patients before and after surgery. DESIGN Serum samples of eight newly diagnosed acromegaly patients before and after transsphenoidal surgery were analyzed for proteomic changes by two-dimensional gel electrophoresis. Protein spots displaying statistically significant changes, pre- versus post-surgery, were identified by mass spectrometry (MS), tandem MS (MS/MS), and western blot analysis. RESULTS Six protein spots displaying decreased intensities after surgery were identified as transthyretin (two isoforms), haptoglobin α2, β-hemoglobin, and apolipoprotein A-1 (two isoforms). One protein spot, identified as complement C4B precursor, was increased after the surgery. CONCLUSIONS Seven serum protein spots were differentially expressed following surgery in acromegalic patients. The identified proteins represent potential novel biomarkers to assess the effectiveness of surgical treatment in acromegalic individuals. Future studies will validate the use of the identified proteins as biomarkers of disease activity after medical treatment of acromegaly.

Identification of New Biomarkers of Low-Dose GH Replacement Therapy in GH-Deficient Patients

CONTEXT GH secretion peaks at puberty and continues to be secreted in adulthood, albeit at a declining rate. Profound GH deficiency (GHD) in adults with pituitary disease is associated with symptoms that improve with GH substitution, but it is important to tailor the GH dose to avoid overtreatment. Measurement of serum IGF-I levels is an important clinical tool in this regard, but it is well recognized that some patients receiving GH treatment do not show an increase in IGF-I. OBJECTIVE The objective of the study was to identify novel serum biomarkers of GH treatment in adults with GHD. DESIGN AND PATIENTS Eight patients with profound GHD as a consequence of a pituitary adenoma or its treatment were evaluated before and 3 months after GH replacement therapy (0.2-0.4 mg/d). MAIN OUTCOME MEASURES Serum proteomic changes were studied using two-dimensional gel electrophoresis and mass spectrometry. Protein profiles were analyzed and compared in serum samples obtained before and after GH treatment. RESULTS The levels of six serum protein spots were significantly altered after GH substitution. These proteins were identified as five isoforms of haptoglobin (decreased in posttreatment samples) and one isoform of apolipoprotein A-I (increased in posttreatment samples). Importantly, changes in the levels of the identified proteins were associated with decreases in fat mass and increases in lean mass in all patients. These results were independent of serum IGF-I levels. CONCLUSIONS Evaluation of the identified proteins provides a novel alternative to traditional markers of GH status, such as serum IGF-I levels, to assess GH therapy in GH deficient adults.

Mouse models of growth hormone action and aging: A proteomic perspective

Growth hormone (GH) is a protein secreted by the anterior pituitary and circulates throughout the body to exert important actions on growth and metabolism. GH stimulates the secretion of insulin‐like growth factor‐I (IGF‐I) that mediates some of the growth promoting actions of GH. The GH/IGF‐I axis has recently been recognized as important in terms of longevity in organisms ranging from Caenorhabditis elegans to mice. For example, GH transgenic mice possess short lifespans while GH receptor null (GHR‒/‒) mice have extended longevity. Thus, the actions of GH (or IGF‐I) or lack thereof impact the aging process. In this review, we summarize the proteomic analyses of plasma and white adipose tissue in these two mouse models of GH action, i.e. GH transgenic and GHR‒/‒ mice. At the protein level, we wanted to establish novel plasma biomarkers of GH action as a function of age and to determine differences in adipose tissue depots. We have shown that these proteomic approaches have not only confirmed several known physiological actions of GH, but also resulted in novel protein biomarkers and targets that may be indicative of the aging process and/or new functions of GH. These results may generate new directions for GH and/or aging research.

Age-Related and Depot-Specific Changes in White Adipose Tissue of Growth Hormone Receptor-Null Mice

Growth hormone receptor-null (GHR(-/-)) mice are dwarf, insulin sensitive, and long-lived in spite of increased adiposity. However, their adiposity is not uniform, with select white adipose tissue (WAT) depots enlarged. To study WAT depot-specific effects on insulin sensitivity and life span, we analyzed individual WAT depots of 12- and 24-month-old GHR(-) (/-) and wild-type (WT) mice, as well as their plasma levels of selected hormones. Adipocyte sizes and plasma insulin, leptin, and adiponectin levels decreased with age in both GHR(-) (/-) and WT mice. Two-dimensional gel electrophoresis proteomes of WAT depots were similar among groups, but several proteins involved in endocytosis and/or cytoskeletal organization (Ehd2, S100A10, actin), anticoagulation (S100A10, annexin A5), and age-related conditions (alpha2-macroglobulin, apolipoprotein A-I, transthyretin) showed significant differences between genotypes. Because Ehd2 may regulate endocytosis of Glut4, we measured Glut4 levels in the WAT depots of GHR(-) (/-) and WT mice. Inguinal WAT of 12-month-old GHR(-) (/-) mice displayed lower levels of Glut4 than WT. Overall, the protein changes detected in this study offer new insights into possible mechanisms contributing to enhanced insulin sensitivity and extended life span in GHR(-) (/-) mice.

Central leptin and insulin administration modulates serum cytokine- and lipoprotein-related markers.

UNLABELLED In most obese patients there is an inflammatory state characterized by lipid abnormalities, hyperleptinemia and hyperinsulinemia. OBJECTIVE The objective was to identify mechanisms involved in leptins role in the attenuation of the response to insulin using a proteomic approach. MATERIAL/METHODS We studied the serum proteomic profile of rats treated by central leptin infusion followed by an injection of insulin. We analyzed the relationship between these proteins and serum cytokine and apolipoprotein levels. RESULTS Out of 81 protein spots, intensity differences were found in 11, corresponding to 5 proteins: three isoforms of α1 macroglobulin; three of haptoglobin and serum amyloid P component-precursor. All of these are acute-phase proteins involved in inflammation and are correlated with cytokine levels. Additionally, two apolipoprotein E and two apolipoprotein A1 isoforms were identified and were found to correlate with LDL and HDL. CONCLUSIONS Our results indicate that increased leptin and insulin levels change these circulating proteins, thus promoting systemic inflammation and changing lipid metabolism.