scholarly journals Effect of mechanical loading on insulin-like growth factor-I gene expression in rat tibia

2007 ◽  
Vol 192 (1) ◽  
pp. 131-140 ◽  
Author(s):  
Christianne M A Reijnders ◽  
Nathalie Bravenboer ◽  
Annechien M Tromp ◽  
Marinus A Blankenstein ◽  
Paul Lips
Keyword(s):  
Bone Formation ◽  
Mrna Expression ◽  
Mechanical Loading ◽  
Mechanical Stimulation ◽  
Molecular Mechanisms ◽  
Bone Marrow Cells ◽  
Mechanical Stimuli ◽  
Igf I ◽  
Female Wistar Rats ◽  
Tibia Shaft

Mechanical loading plays an essential role in maintaining skeletal integrity. Mechanical stimulation leads to increased bone formation. However, the cellular and molecular mechanisms that are involved in the translation of mechanical stimuli into bone formation, are not completely understood. Growth factors and osteocytes, which act as mechanosensors, play a key role during the bone formation after mechanical stimulation. The aim of this study was to characterize the role of IGF-I in the translation of mechanical stimuli into bone formation locally in rat tibiae. Fifteen female Wistar rats were randomly assigned to three groups (n = 5): load, sham-loaded, and control. The four-point bending model of Forwood and Turner was used to induce a single period of mechanical loading on the tibia shaft. The effects of mechanical loading on IGF-I mRNA expression were determined with non-radioactive in situ hybridization on decalcified tibiae sections, 6 h after the loading session. Endogenous IGF-I mRNA was expressed in trabecular and cortical osteoblasts, some trabecular and sub-endocortical osteocytes, intracortical endothelial cells of blood vessels, and periosteum. Megakaryocytes, macrophages, and myeloid cells also expressed IGF-I mRNA. In the growth plate, IGF-I mRNA was located in proliferative and hypertrophic chondrocytes. Mechanical loading did not affect the IGF-I mRNA expression in osteoblasts, bone marrow cells, and chondrocytes, but the osteocytes at the endosteal side of the shaft showed a twofold increase of IGF-I mRNA expression. The proportion of IGF-I mRNA positive osteocytes in loaded tibiae was 29.3 ± 12.9% (mean ± s.d.; n = 5), whereas sham-loaded and contra-lateral control tibiae exhibited 16.7 ± 4.4% (n = 5) and 14.7 ± 4.2% (n = 10) respectively (P < 0.05). Lamellar bone formation after a single mechanical loading session was observed at the endosteal side of the shaft. In conclusion, a single loading session results in a twofold up-regulation of IGF-I mRNA synthesis in osteocytes which are present in multiple layers extending into the cortical bone of mechanically stimulated tibia shaft 6 h after loading. This supports the hypothesis that IGF-I, which is located in osteocytes, is involved in the translation of mechanical stimuli into bone formation.

scholarly journals Wnt5a/FZD4 Mediates the Mechanical Stretch-Induced Osteogenic Differentiation of Bone Mesenchymal Stem Cells

2018 ◽  
Vol 48 (1) ◽  
pp. 215-226 ◽  
Author(s):  
Qingguo Gu ◽  
Haijun Tian ◽  
Kai Zhang ◽  
Deyu Chen ◽  
Dechun Chen ◽  
...  
Keyword(s):  
Bone Formation ◽  
Osteogenic Differentiation ◽  
Mechanical Loading ◽  
Mechanical Stimulation ◽  
Mechanical Stretch ◽  
Wnt Signalling ◽  
Hindlimb Unloading ◽  
Mechanical Stimuli ◽  
Bone Mesenchymal Stem Cells ◽  
Alizarin Red

Background/Aims: Mechanical stimulation and WNT signalling have essential roles in regulating the osteogenic differentiation of bone marrow stromal cells (BMSCs) and bone formation. However, little is known regarding the regulation of WNT signalling molecule expression and therefore the osteogenic differentiation of BMSCs during osteogenesis. Methods: Microarrays of BMSCs from elderly individuals or patients with osteoporosis (GSE35959) from the GEO database were analysed using GeneSight-Lite 4.1.6 (BioDiscovery) and C2 curated gene sets downloaded from Molecular Signatures Database (MSigDB). Realtime PCR and western blotting were used to measure the expression of the indicated genes. ALP and Alizarin red staining were used to evaluate the osteogenesis of BMSCs. Results: In this study, we investigated whether mechanical loading directly regulates the expression of WNT signalling molecules and examined the role of WNT signalling in mechanical loading-triggered osteogenic differentiation and bone formation. We first studied the microarrays of samples from patients with osteoporosis and found downregulation of the GPCR ligand binding gene set in the BMSCs of patients with osteoporosis. Then, we demonstrated that mechanical stimuli can regulate osteogenesis and bone formation both in vivo and in vitro. FZD4 was upregulated during cyclic mechanical stretch (CMS)-induced osteogenic differentiation, and the JNK signalling pathway was activated. FZD4 knockdown inhibited the mechanical stimuli-induced osteogenesis and JNK activity. More importantly, we found an activating effect of WNT5A and FZD4 that regulated bone formation in response to hindlimb unloading in mice, and pretreatment with WNT5A or activation of the expression of FZD4 partly rescued the osteoporosis caused by mechanical unloading. Conclusions: Our results demonstrate, for the first time, that mechanical stimulation alters the expression of genes involved in the osteogenic differentiation of BMSCs via the direct regulation of FZD4 and that therapeutic WNT5A and FZD saRNA may be an efficient strategy for enhancing bone formation under mechanical stimulation.

scholarly journals Insulin receptor substrate-2 maintains predominance of anabolic function over catabolic function of osteoblasts

2002 ◽  
Vol 159 (1) ◽  
pp. 147-156 ◽  
Author(s):  
Toru Akune ◽  
Naoshi Ogata ◽  
Kazuto Hoshi ◽  
Naoto Kubota ◽  
Yasuo Terauchi ◽  
...  
Keyword(s):  
Bone Resorption ◽  
Bone Formation ◽  
Insulin Receptor ◽  
Intracellular Signaling ◽  
Bone Marrow Cells ◽  
Adenovirus Vector ◽  
Nuclear Factor Κb ◽  
Insulin Receptor Substrates ◽  
Anabolic Action ◽  
Igf I

Insulin receptor substrates (IRS-1 and IRS-2) are essential for intracellular signaling by insulin and insulin-like growth factor-I (IGF-I), anabolic regulators of bone metabolism. Although mice lacking the IRS-2 gene (IRS-2−/− mice) developed normally, they exhibited osteopenia with decreased bone formation and increased bone resorption. Cultured IRS-2−/− osteoblasts showed reduced differentiation and matrix synthesis compared with wild-type osteoblasts. However, they showed increased receptor activator of nuclear factor κB ligand (RANKL) expression and osteoclastogenesis in the coculture with bone marrow cells, which were restored by reintroduction of IRS-2 using an adenovirus vector. Although IRS-2 was expressed and phosphorylated by insulin and IGF-I in both osteoblasts and osteoclastic cells, cultures in the absence of osteoblasts revealed that intrinsic IRS-2 signaling in osteoclastic cells was not important for their differentiation, function, or survival. It is concluded that IRS-2 deficiency in osteoblasts causes osteopenia through impaired anabolic function and enhanced supporting ability of osteoclastogenesis. We propose that IRS-2 is needed to maintain the predominance of bone formation over bone resorption, whereas IRS-1 maintains bone turnover, as we previously reported; the integration of these two signalings causes a potent bone anabolic action by insulin and IGF-I.

scholarly journals The nucleocytoplasmic shuttling protein CIZ reduces adult bone mass by inhibiting bone morphogenetic protein–induced bone formation

2005 ◽  
Vol 201 (6) ◽  
pp. 961-970 ◽  
Author(s):  
Mikihiko Morinobu ◽  
Tetsuya Nakamoto ◽  
Kazunori Hino ◽  
Kunikazu Tsuji ◽  
Zhong-Jian Shen ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Bone Formation ◽  
Bone Mass ◽  
Mrna Expression ◽  
Bone Marrow Cells ◽  
Nucleocytoplasmic Shuttling ◽  
Morphogenetic Protein ◽  
Adult Bone ◽  
Deficient Mice

Osteoporosis is a major health problem; however, the mechanisms regulating adult bone mass are poorly understood. Cas-interacting zinc finger protein (CIZ) is a nucleocytoplasmic shuttling protein that localizes at cell adhesion plaques that form where osteoblasts attach to substrate. To investigate the potential role of CIZ in regulating adult bone mass, we examined the bones in CIZ-deficient mice. Bone volume was increased and the rates of bone formation were increased in CIZ-deficient mice, whereas bone resorption was not altered. CIZ deficiency enhanced the levels of mRNA expression of genes encoding proteins related to osteoblastic phenotypes, such as alkaline phosphatase (ALP) as well as osterix mRNA expression in whole long bones. Bone marrow cells obtained from the femora of CIZ-deficient mice revealed higher ALP activity in culture and formed more mineralized nodules than wild-type cells. CIZ deficiency enhanced bone morphogenetic protein (BMP)–induced osteoblastic differentiation in bone marrow cells in cultures, indicating that BMP is the target of CIZ action. CIZ deficiency increased newly formed bone mass after femoral bone marrow ablation in vivo. Finally, BMP-2–induced bone formation on adult mouse calvariae in vivo was enhanced by CIZ deficiency. These results establish that CIZ suppresses the levels of adult bone mass through inhibition of BMP-induced activation of osteoblasts.

Osteocytes and WNT: the Mechanical Control of Bone Formation

2010 ◽  
Vol 89 (4) ◽  
pp. 331-343 ◽  
Author(s):  
C. Galli ◽  
G. Passeri ◽  
G.M. Macaluso
Keyword(s):  
Mechanical Properties ◽  
Bone Formation ◽  
Cell Fate ◽  
Mechanical Loading ◽  
Osteoblastic Differentiation ◽  
Mechanical Stimuli ◽  
Master Regulators ◽  
Bone Maintenance ◽  
Skeletal Homeostasis ◽  
Encoding Gene

Mechanical loading is of pivotal importance in the maintenance of skeletal homeostasis, but the players involved in the transduction of mechanical stimuli to promote bone maintenance have long remained elusive. Osteocytes, the most abundant cells in bone, possess mechanosensing appendices stretching through a system of bone canaliculi. Mechanical stimulation plays an important role in osteocyte survival and hence in the preservation of bone mechanical properties, through the maintenance of bone hydratation. Osteocytes can also control the osteoblastic differentiation of mesenchymal precursors in response to mechanical loading by modulating WNT signaling pathways, essential regulators of cell fate and commitment, through the protein sclerostin. Mutations of Sost, the sclerostin-encoding gene, have dramatic effects on the skeleton, indicating that osteocytes may act as master regulators of bone formation and localized bone remodeling. Moreover, the development of sclerostin inhibitors is opening new possibilities for bone regeneration in orthopedics and the dental field.

scholarly journals Mechanical Loading Shows Anti-Myeloma Effects While Rescuing Bone Loss with Net Bone Formation in a Myeloma Bone Disease Murine Model

Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 3164-3164
Author(s):  
Fani Ziouti ◽  
Maximilian Rummler ◽  
Andreas Brandl ◽  
Andreas Beilhack ◽  
Maureen Lynch ◽  
...  
Keyword(s):  
Bone Resorption ◽  
Bone Loss ◽  
Bone Formation ◽  
Bone Remodeling ◽  
Mechanical Loading ◽  
Bone Disease ◽  
Whole Body ◽  
Enzyme Linked Immunosorbent Assay ◽  
Mechanical Stimuli

Abstract Osteolytic bone disease (BD) is a hallmark of multiple myeloma (MM) with tumor cells in the bone marrow shifting the balance of the bone remodeling process towards massive bone resorption. As a result, patients develop devastating osteolytic lesions that lead to non-healing bone fractures and pain, affecting life quality and mortality rates. Bones have the capacity to adapt mass and structure to mechanical stimuli, as dramatically seen in young tennis athletes with muscle-bone asymmetries in the playing arm. We have previously shown that tibial mechanical loading rescued bone loss in our murine MOPC315.BM MM model with an advanced osteolytic phenotype. Here, we hypothesize that mechanical strain (1) modulates the bone microenvironment and (2) has antitumor activity in mice. (1) We determined bone formation and bone resorption parameters by time-lapsed microCT analysis to show how skeletal mechanical stimuli control MM bone disease (MMBD) progression over time. (2) To monitor tumor progression, we used non-invasive bioluminescence imaging (BLI) and enzyme-linked immunosorbent assay (ELISA) for detection of MOPC315.BM specific immunoglobulin A (IgA) levels. In our in vivo loading study, we injected MOPC315.BM cells intratibially (i.t.) in BALB/c mice to establish MMBD (n=17) and used PBS-injected (n=13) as well as noninjected mice (n=8) as controls. Eight (MM), seven (PBS) and 8 (noninjected) mice received compressive tibial loading for three weeks while nine (MM) and six (PBS) mice served as nonloaded controls. The bone remodeling response to mechanical loading was investigated by longitudinal in vivo microCT imaging performed every 5 days (at day 13, 18, 23, 28, and 33 after i.t. injection). MicroCT images from day 33 were geometrically registered onto images of day 13 and resampled into the same coordinate system using Amira and scripts written in Matlab for post-processing. Normalized newly mineralized and eroded bone volume (MV/BV, EV/BV), normalized formed and eroded bone surface area (MS/BS, ES/BS), mineralized thickness (MTh) and eroded depth (ED) were quantified. ANOVA was performed to examine the effect of loading and injection. Loading significantly increased the periosteal MV/BV, periosteal and endosteal MS/BS as well as decreased the periosteal EV/BV and periosteal and endocortical ES/BS. Endosteal MV/BV or EV/BV were not affected, which may be due to differences in the local strain environment at the two surfaces. In addition, mechanical stimuli did not influence ED, but led to diminished periosteal EV/BV and periosteal ES/BS suggesting fewer resorption sites in tibiae subjected to loading. Injection significantly affected periosteal and endosteal bone formation and resorption (Fig.1). Significant increases in cortical bone mass of loaded MM mice were accompanied by decreases in tumor load as evidenced by MOPC315.BM specific IgA levels (Fig. 2A). Interestingly, quantification of tibial and whole body bioluminescence signal intensities revealed controlled tumor growth in the loaded left tibia and a further delay of tumor cell dissemination throughout body of MM mice (Fig. 2B). Our data provide evidence that skeletal mechanical stimuli have anti-myeloma effects and rescue osteolytic bone loss in MMBD. The anabolic response to mechanical loads outweighs the anti-resorptive effect of MM cells, suggesting a combination of loading with bone resorption inhibitors in future therapeutic strategies. Disclosures No relevant conflicts of interest to declare.

scholarly journals Role of CaMKK2 in Mechanically Induced Bone Formation

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Adam J. Warrick ◽  
Uma Sankar
Keyword(s):  
Protein Kinase ◽  
Bone Density ◽  
Bone Formation ◽  
Mechanical Stimulation ◽  
Internal Control ◽  
Molecular Mechanisms ◽  
Bone Growth ◽  
Lower Limbs ◽  
Alizarin Red ◽  
Bone Formation Rate

Background and Hypothesis: Mechanical stimulation of bone results in the translation of external forces into a cascade of structural and biochemical changes which work to increase bone density and decrease fracture healing time. The specific mechanisms contributing to these processes are areas of active investigation. Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2) is a serine-threonine protein kinase with key roles in both the anabolic and catabolic pathways of bone remodeling. We hypothesize that the absence of CaMKK2 potentiates an increase in bone density as a response to mechanical stimulation. Experimental Design or Project Methods: The right ulna of anesthetized C57BL/6 mice were loaded for 220 cycles at 2 Hz and with peak forces specific to both sex and genotype. Loading was completed using an electro actuator (Bose ElectroForce 3200; EnduraTEC, Minnetonka, MN, USA) and was repeated on days 3, 5, 8 and 10 after the initial procedure. The non-loaded left ulna served as an internal control. Calcein and alizarin red were administered intraperitoneally on days 9 and 16 respectively. Mice were sacrificed on day 19 after the initial load; blood and long bones of the lower limbs were collected for analysis. Results: Bone volumetric analyses will be measured using microcomputed tomography, bone formation rate will be assessed using dynamic histomorphometry measurements of double fluorochrome labeling, and cellular and molecular mechanisms will be assessed using histology, immunohistochemistry and real-time reverse transcription-polymerase chain reaction. These data are currently forthcoming. Conclusion and Potential Impact: Clinical outcomes of conditions ranging from stress fractures to osteoporosis may be improved by an increased understanding of the mechanisms through which bone growth is augmented. Expanded knowledge of these pathways may provide opportunities for the development of novel therapies which decrease healing times in the event of injury and increase bone density to combat degenerative disease states.

Osteocytic expression of mRNA for c-fos and IGF-I: an immediate early gene response to an osteogenic stimulus

1996 ◽  
Vol 270 (6) ◽  
pp. E937-E945 ◽  
Author(s):  
J. M. Lean ◽  
A. G. Mackay ◽  
J. W. Chow ◽  
T. J. Chambers
Keyword(s):  
Growth Factor ◽  
Mrna Expression ◽  
Mechanical Stimulation ◽  
Early Gene ◽  
Factor I ◽  
Gene Response ◽  
Osteogenic Response ◽  
Igf I ◽  
I Gene ◽  
Stimulation Of

We analyzed the expression, during the osteogenic response of bone to mechanical stimulation, of insulin-like growth factor I (IGF-I), a growth factor implicated in bone formation, and c-fos, a protooncogene in which disordered regulation specifically affects bone. Both genes were strongly expressed in osteocytes of mechanically stimulated but not control bones within 30 min of the osteogenic stimulus. IGF-I mRNA expression increased up to 6 h, was restricted to osteocytes, and was strongly suppressed by indomethacin. Although early IGF-I mRNA expression was resistant to cycloheximide, there was a degree of suppression after 6 h, raising the possibility that IGF-I expression might be prolonged by autocrine mechanisms. c-fos mRNA was increased both in osteocytes and on bone surfaces. At both sites, c-fos expression was transient, prolonged by cycloheximide, and was strongly stimulated even in the presence of indomethacin. Thus osteocytes respond to mechanical stimulation with immediate prolonged expression of IGF-I and immediate transient expression of c-fos, implicating osteocytes in the osteogenic response to mechanical stimulation. Moreover, the different spatial distribution and indomethacin sensitivity of c-fos and IGF-I gene expression suggest that at least two signaling pathways are activated in osteocytes during this process.

scholarly journals Investigating the mechanistic basis of biomechanical input controlling skeletal development: exploring the interplay with Wnt signalling at the joint

2018 ◽  
Vol 373 (1759) ◽  
pp. 20170329 ◽  
Author(s):  
Rebecca A. Rolfe ◽  
Claire A. Shea ◽  
Pratik Narendra Pratap Singh ◽  
Amitabha Bandyopadhyay ◽  
Paula Murphy
Keyword(s):  
Mechanical Stimulation ◽  
Wnt Pathway ◽  
Molecular Mechanisms ◽  
Skeletal Development ◽  
Wnt Signalling ◽  
Mechanical Stimuli ◽  
Mechanistic Basis ◽  
Bmp Signalling ◽  
Canonical Wnt ◽  
Mechanical Influence

Embryo movement is essential to the formation of a functional skeleton. Using mouse and chick models, we previously showed that mechanical forces influence gene regulation and tissue patterning, particularly at developing limb joints. However, the molecular mechanisms that underpin the influence of mechanical signals are poorly understood. Wnt signalling is required during skeletal development and is altered under reduced mechanical stimulation. Here, to explore Wnt signalling as a mediator of mechanical input, the expression of Wnt ligand and Fzd receptor genes in the developing skeletal rudiments was profiled. Canonical Wnt activity restricted to the developing joint was shown to be reduced under immobilization, while overexpression of activated β-catenin following electroporation of chick embryo limbs led to joint expansion, supporting the proposed role for Wnt signalling in mechanoresponsive joint patterning. Two key findings advance our understanding of the interplay between Wnt signalling and mechanical stimuli: first, loss of canonical Wnt activity at the joint shows reciprocal, coordinated misregulation of BMP signalling under altered mechanical influence. Second, this occurs simultaneously with increased expression of several Wnt pathway component genes in a territory peripheral to the joint, indicating the importance of mechanical stimulation for a population of potential joint progenitor cells. This article is part of the Theo Murphy meeting issue ‘Mechanics of Development’.

BONE ADAPTATION AND REGENERATION – NEW DEVELOPMENTS

2012 ◽  
Vol 17 ◽  
pp. 34-43 ◽  
Author(s):  
JENNEKE KLEIN-NULEND ◽  
ROMMEL GAUD BACABAC
Keyword(s):  
Bone Formation ◽  
Cell Signaling ◽  
Mechanical Loading ◽  
Bone Structure ◽  
Bone Cells ◽  
Mechanical Energy ◽  
Bone Adaptation ◽  
Mechanical Stimuli ◽  
Waste Products ◽  
Local Bone

Bone is a dynamic tissue that is constantly renewed and adapts to its local loading environment. Mechanical loading results in adaptive changes in bone size and shape that strengthen bone structure. The mechanisms for adaptation involve a multistep process called mechanotransduction, which is the ability of resident bone cells to perceive and translate mechanical energy into a cascade of structural and biochemical changes within the cells. The transduction of a mechanical signal to a biochemical response involves pathways within the cell membrane and cytoskeleton of the osteocytes, the professional mechansensor cells of bone. During the last decade the role of mechanosensitive osteocytes in bone metabolism and turnover, and the lacuno-canalicular porosity as the structure that mediates mechanosensing, is likely to reveal a new paradigm for understanding the bone formation response to mechanical loading, and the bone resorption response to disuse. Strain-derived fluid flow of interstitial fluid through the lacuno-canalicular porosity seems to mechanically activate the osteocytes, as well as ensures transport of cell signaling molecules, nutrients and waste products. Cell-cell signaling from the osteocyte sensor cells to the effector cells (osteoblasts or osteoclasts), and the effector cell response – either bone formation or resorption, allow an explanation of local bone gain and loss as well as remodeling in response to fatigue damage as processes supervised by mechanosensitive osteocytes. The osteogenic activity of cultured bone cells has been quantitatively correlated with varying stress stimulations highlighting the importance of the rate of loading. Theoretically a possible mechanism for the stress response by osteocytes is due to strain amplification at the pericellular matrix. Single cell studies on molecular responses of osteocytes provide insight on local architectural alignment in bone during remodeling. Alignment seems to occur as a result of the osteocytes sensing different canalicular flow patterns around cutting cone and reversal zone during loading, thus determining the bone's structure. Disturbances in architecture and permeability of the 3D porous network will affect transduction of mechanical loads to the mechanosensors. Uncovering the cellular and mechanical basis of the osteocyte's response to loading represents a significant challenge to our understanding of cellular mechanotransduction and bone remodeling. In view of the importance of mechanical stress for maintaining bone strength, mechanical stimuli have great potential for providing a therapeutic approach for bone (re)generation.

scholarly journals Potential Role of Growth Hormone in Impairment of Insulin Signaling in Skeletal Muscle, Adipose Tissue, and Liver of Rats Chronically Treated with Arginine

Endocrinology ◽  
2008 ◽  
Vol 150 (5) ◽  
pp. 2080-2086 ◽  
Author(s):  
Thais de Castro Barbosa ◽  
José Edgar Nicoletti de Carvalho ◽  
Leonice Lourenço Poyares ◽  
Silvana Bordin ◽  
Ubiratan Fabres Machado ◽  
...  
Keyword(s):  
Adipose Tissue ◽  
Mrna Expression ◽  
Insulin Signaling ◽  
Molecular Mechanisms ◽  
Glucose Transporter ◽  
Total Content ◽  
Chronic Administration ◽  
Janus Kinase ◽  
Janus Kinase 2 ◽  
Igf I

We have shown that rats chronically treated with Arginine (Arg), although normoglycemic, exhibit hyperinsulinemia and decreased blood glucose disappearance rate after an insulin challenge. Attempting to investigate the processes underlying these alterations, male Wistar rats were treated with Arg (35 mg/d), in drinking water, for 4 wk. Rats were then acutely stimulated with insulin, and the soleus and extensorum digitalis longus muscles, white adipose tissue (WAT), and liver were excised for total and/or phosphorylated insulin receptor (IR), IR substrate 1/2, Akt, Janus kinase 2, signal transducer and activator of transcription (STAT) 1/3/5, and p85α/55α determination. Muscles and WAT were also used for plasma membrane (PM) and microsome evaluation of glucose transporter (GLUT) 4 content. Pituitary GH mRNA, GH, and liver IGF-I mRNA expression were estimated. It was shown that Arg treatment: 1) did not affect phosphotyrosine-IR, whereas it decreased phosphotyrosine-IR substrate 1/2 and phosphoserine-Akt content in all tissues studied, indicating that insulin signaling is impaired at post-receptor level; 2) decreased PM GLUT4 content in both muscles and WAT; 3) increased the pituitary GH mRNA, GH, and liver IGF-I mRNA expression, the levels of phosphotyrosine-STAT5 in both muscles, phosphotyrosine-Janus kinase 2 in extensorum digitalis longus, phosphotyrosine-STAT3 in liver, and WAT as well as total p85α in soleus, indicating that GH signaling is enhanced in these tissues; and 4) increased p55α total content in muscles, WAT, and liver. The present findings provide the molecular mechanisms by which insulin resistance and, by extension, reduced GLUT4 content in PM of muscles and WAT take place after chronic administration of Arg, and further suggest a putative role for GH in its genesis, considering its diabetogenic effect.

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