Faculty Bibliography

Mitochondrial permeability transition (PT) is a phenomenon of stress-induced increase in nonspecific permeability of the mitochondrial inner membrane that leads to disruption of oxidative phosphorylation and cell death. Quantitative measurement of the membrane permeability increase during PT is critically important for understanding the PT's impact on mitochondrial function. The elementary unit of PT is a PT pore (PTP), a single channel presumably formed by either ATP synthase or adenine nucleotide translocator (ANT). It is not known how many channels are open in a single mitochondrion during PT, which makes it difficult to quantitatively estimate the overall degree of membrane permeability. Here, we used wide-field microscopy to record mitochondrial swelling and quantitatively measure rates of single-mitochondrion volume increase during PT-induced high-amplitude swelling. PT was quantified by calculating the rates of water flux responsible for measured volume changes. The total water flux through the mitochondrial membrane of a single mitochondrion during PT was in the range of (2.5 ± 0.4) × 10-17 kg/s for swelling in 2 mM Ca2+ and (1.1 ± 0.2) × 10-17 kg/s for swelling in 200 µM Ca2+. Under these experimental conditions, a single PTP channel with ionic conductance of 1.5 nS could allow passage of water at the rate of 0.65 × 10-17 kg/s. Thus, we estimate the integral ionic conductance of the whole mitochondrion during PT to be 5.9 ± 0.9 nS for 2 mM concentration of Ca2+ and 2.6 ± 0.4 nS for 200 µM of Ca2+. The number of PTPs per mitochondrion ranged from one to nine. Due to the uncertainties in PTP structure and model parameters, PTP count results may be slightly underestimated. However, taking into account that each mitochondrion has ∼15,000 copies of ATP synthases and ANTs, our data imply that PTP activation is a rare event that occurs only in a small subpopulation of these proteins.

A rare 20K isoform of GH-V (here abbreviated as GHv) was discovered in 1998. To date, only 1 research article has characterized this isoform in vivo, observing that GHv treatment in male high-fat fed rats had several GH-like activities, but unlike GH lacked diabetogenic and lactogenic activities and failed to increase IGF-1 or body length. Therefore, the current study was conducted to further characterize the in vivo activities of GHv in a separate species and in a GH-deficient model (GH-/- mice) and with both sexes represented. GHv-treated GH-/- mice had significant increases to serum IGF-1, femur length, body length, body weight, and lean body mass and reduced body fat mass similar to mice receiving GH treatment. GH treatment increased circulating insulin levels and impaired insulin sensitivity; in contrast, both measures were unchanged in GHv-treated mice. Since GHv lacks prolactin receptor (PRLR) binding activity, we tested the ability of GH and GHv to stimulate the proliferation of human cancer cell lines and found that GHv has a decreased proliferative response in cancers with high PRLR. Our findings demonstrate that GHv can stimulate insulin-like growth factor-1 and subsequent longitudinal body growth in GH-deficient mice similar to GH, but unlike GH, GHv promoted growth without inhibiting insulin action and without promoting the growth of PRLR-positive cancers in vitro. Thus, GHv may represent improvements to current GH therapies especially for individuals at risk for metabolic syndrome or PRLR-positive cancers.

The mitochondria are key organelles regulating vital processes in the eukaryote cell. A decline in mitochondrial function is one of the hallmarks of aging. Growth hormone (GH) and the insulin-like growth factor-1 (IGF-1) are somatotropic hormones that regulate cellular homeostasis and play significant roles in cell differentiation, function, and survival. In mammals, these hormones peak during puberty and decline gradually during adulthood and aging. Here, we review the evidence that GH and IGF-1 regulate mitochondrial mass and function and contribute to specific processes of cellular aging. Specifically, we discuss the contribution of GH and IGF-1 to mitochondrial biogenesis, respiration and ATP production, oxidative stress, senescence, and apoptosis. Particular emphasis was placed on how these pathways intersect during aging.

The insulin-like growth factors (IGF) have a key role in the development of gynecological cancers, including endometrial tumors. Uterine serous carcinoma (USC) constitutes a defined histological category among endometrial cancers. Laron syndrome (LS) is a genetic type of dwarfism that results from mutation of the growth hormone receptor (GHR) gene, and is the best characterized entity under the spectrum of the congenital IGF1 deficiencies. Epidemiological studies have shown that LS patients are protected from cancer development. Recent genome-wide association studies conducted on LS-derived lymphoblastoid cells led to the identification of a series of metabolic genes whose over-representation in this condition might be linked to cancer protection. Our analyses led to the identification of ZYG11A, a potential cell cycle regulator, as a new downstream target for IGF1 action. The aim of the present paper was to investigate the regulation of ZYG11A gene expression by IGF1 and insulin in endometrial cancer cell lines and to assess the impact of tumor suppressor p53 on ZYG11A expression and biological action. Using USC-derived cell lines expressing a wild type or a mutant p53 gene, we demonstrate that IGF1 inhibited ZYG11A mRNA and protein levels in cells containing a wild type p53. On the other hand, IGF1 potently stimulated ZYG11A expression in mutant p53-expressing cells. Data presented here links the IGF1 and p53 signaling pathways with ZYG11A action. The clinical implications of the present study in endometrial and other types of cancer must be further investigated.

Laron syndrome (LS), or primary growth hormone resistance, is a prototypical congenital insulin-like growth factor 1 (IGF1) deficiency. The recent epidemiological finding that LS patients do not develop cancer is of major scientific and clinical relevance. Epidemiological data suggest that congenital IGF1 deficiency confers protection against the development of malignancies. This 'experiment of nature' reflects the critical role of IGF1 in tumor biology. The present review article provides an overview of recently conducted genome-wide profiling analyses aimed at identifying mechanisms and signaling pathways that are directly responsible for the link between life-time low IGF1 levels and protection from tumor development. The review underscores the concept that 'data mining' an orphan disease might translate into new developments in oncology.

Bioactive free insulin-like growth factor (IGF-I) is critically important for growth. The bioavailability of IGF-I is modulated by the IGF-binding proteins and their proteases, such as pregnancy-associated plasma protein-A2 (PAPP-A2). We have created a mouse model with a specific mutation in PAPPA2 identified in a human with PAPP-A2 deficiency. The human mutation was introduced to the mouse genome via a knock-in strategy, creating knock-in mice with detectable protein levels of Papp-a2 but without protease activities. We found that the Pappa2 mutation led to significant reductions in body length (10%), body weight (10% and 20% in males and females, respectively), and relative lean mass in mice. Micro-CT analyses of Pappa2 knock-in femurs from adult mice showed inhibited periosteal bone expansion leading to more slender bones in both male and female mice. Furthermore, in the Pappa2 knock-in mice, insulin resistance correlated with decreased serum free IGF-I and increased intact IGFBP-3 concentrations. Interestingly, mice heterozygous for the knock-in mutation demonstrated a growth rate for body weight and length as well as a biochemical phenotype that was intermediate between wild-type and homozygous mice. This is the first study modeling a human PAPPA2 mutation in mice. The mouse phenotype closely resembles that of the human patients, and provides further evidence that the regulation of IGF-I bioavailability by PAPP-A2 is critical for human growth and for glucose and bone metabolism.

Despite increased longevity and resistance to multiple stressors, growth hormone receptor null (GHRKO) mice exhibit severe skeletal impairment. The role of GHR in maintaining osteocyte mitochondrial function is unknown. We found that GHR ablation was detrimental to osteocyte mitochondrial function. In vivo multiphoton microscopy revealed significant reductions of >10% in mitochondrial membrane potential (MMP) in GHRKO osteocytes and reduced mitochondrial volumetric density. Reductions in MMP were accompanied by reductions in glucose transporter-1 levels, steady state ATP, NADH redox index, oxygen consumption rate, and mitochondrial reserve capacity in GHRKO osteocytes. Glycolytic capacity did not differ between control and GHRKO males' osteocytes. However, osteocytes from aged female GHRKO mice exhibited reductions in glycolytic parameters, indicating impairments in glucose metabolism, which may be sex dependent. GHRKO osteocytes exhibited increased levels of cytoplasmic reactive oxygen species (ROS) (both basal and in response to high glucose), insulin-like growth factor-1 (IGF-1), and insulin. Mitochondrial ROS levels were increased and correlated with reduced glutathione in GHRKO osteocytes. Overall, the compromised osteocyte mitochondrial function and responses to metabolic insults strongly correlated with skeletal impairments, suggesting that despite increased life span of the GHRKO mice, skeletal health span is decreased. © 2018 American Society for Bone and Mineral Research.