Effects of elevated circulating IGF-1 on the extracellular matrix in "high-growth" C57BL/6J mice

The Role of IGF/IGF-IR-Signaling and Extracellular Matrix Effectors in Bone Sarcoma Pathogenesis

Simple Summary

Bone sarcomas are mesenchymal origin tumors. Bone sarcoma patients show a variable response or do not respond to chemotherapy. Notably, improving efficient chemotherapy approaches, dealing with chemoresistance, and preventing metastasis pose unmet challenges in sarcoma therapy. Insulin-like growth factors 1 and 2 (IGF-1 and -2) and their respective receptors are a multifactorial system that significantly contributes to bone sarcoma pathogenesis. Most clinical trials aiming at the IGF pathway have had limited success. Developing combinatorial strategies to enhance antitumor responses and better classify the patients that could best benefit from IGF-axis targeting therapies is in order. A plausible approach for developing a combinatorial strategy is to focus on the tumor microenvironment (TME) and processes executed therein. Herewith, we will discuss how the interplay between IGF-signaling and the TME constituents affects bone sarcomas’ basal functions and their response to therapy. Potential direct and adjunct therapeutical implications of the extracellular matrix (ECM) effectors will also be summarized.

Abstract

Bone sarcomas, mesenchymal origin tumors, represent a substantial group of varying neoplasms of a distinct entity. Bone sarcoma patients show a limited response or do not respond to chemotherapy. Notably, developing efficient chemotherapy approaches, dealing with chemoresistance, and preventing metastasis pose unmet challenges in sarcoma therapy. Insulin-like growth factors 1 and 2 (IGF-1 and -2) and their respective receptors are a multifactorial system that significantly contributes to bone sarcoma pathogenesis. Whereas failures have been registered in creating novel targeted therapeutics aiming at the IGF pathway, new agent development should continue, evaluating combinatorial strategies for enhancing antitumor responses and better classifying the patients that could best benefit from these therapies. A plausible approach for developing a combinatorial strategy is to focus on the tumor microenvironment (TME) and processes executed therein. Herewith, we will discuss how the interplay between IGF-signaling and the TME constituents affects sarcomas’ basal functions and their response to therapy. This review highlights key studies focusing on IGF signaling in bone sarcomas, specifically studies underscoring novel properties that make this system an attractive therapeutic target and identifies new relationships that may be exploited. Potential direct and adjunct therapeutical implications of the extracellular matrix (ECM) effectors will also be summarized.

SOCS2 Silencing Improves Somatic Growth without Worsening Kidney Function in CKD

BACKGROUND

Growth hormone (GH) resistance in CKD is partly due to increased expression of SOCS2, a GH signaling negative regulator. In SOCS2 absence, body growth is exaggerated. However, GH overexpression in mice causes glomerulosclerosis. Accordingly, we tested whether lack of SOCS2 improves body growth, but accelerates kidney damage in CKD.

METHODS

Eight-week-old mutant SOCS2-deficient high growth (HG) and normal wild-type mice (N) underwent 5/6 nephrectomy (CKD) or sham operation (C) and were sacrificed after 12 weeks, generating 4 groups: C-N, C-HG, CKD-N, CKD-HG.

RESULTS

Somatic growth, inhibited in CKD-N, increased significantly in CKD-HG. Liver p-STAT5, a key intracellular signal of GH receptor (GHR) activation, was decreased in CKD-N but not in CKD-HG. Serum Cr as well as histopathological scores of renal fibrosis were similar in both CKD groups. Kidney fibrogenic (TGF-β and collagen type IV mRNA) and inflammatory precursors (IL6, STAT3, and SOCS3 mRNA) were similarly increased in C-HG, CKD-HG, and CKD-N versus C-N. Renal GHR mRNA was decreased in C-HG, CKD-HG, and CKD-N versus C-N. Kidney p-STAT5 was decreased in CKD-N but not elevated in CKD-HG.

CONCLUSIONS

CKD-related growth retardation is overcome by SOCS2 silencing, in association with increased hepatic STAT5 phosphorylation. Renal insufficiency is not worsened by SOCS2 absence, as kidney GHR and STAT5 are not upregulated. This may be due to elevated kidney proinflammatory cytokines and their mediators, phospho-STAT3 and SOCS3, which may counteract for the absence in SOCS2 and explain the renal safety of prolonged GH therapy in CKD.

MEAT SCIENCE AND MUSCLE BIOLOGY SYMPOSIUM: BIOLOGICAL INFLUENCERS OF MEAT PALATABILITY: Production factors affecting the contribution of collagen to beef toughness1,2

Intramuscular collagen may affect the value of meat by limiting its tenderness and cooking convenience. Production factors such as age of animal at slaughter, the use of steroids and beta-adrenergic agonists as growth promotants, and cattle breed may affect the contribution of collagen to beef quality. Recent research has indicated that concentrations of the mature collagen cross-link pyridinoline (PYR) are positively correlated with Warner-Bratzler shear force (WBSF) and animal age at slaughter, while contribution of the concentration of a second mature collagen cross-link Ehrlich's Chromogen (EC) to beef toughness declines with cattle age. Cattle breed influences total collagen content of muscle due to differing rates of maturation among breeds. Growth promoting technologies do not appear to affect collagen solubility, but do influence PYR and EC densities and concentrations in some beef muscles. Concentrations of PYR and EC do not account for all the variation in collagen heat solubility in beef muscles, nor do advanced glycation end products given the relative immaturity of cattle at slaughter. In light of this, other collagen cross-links such as heat-stable divalent cross-links may warrant reconsideration with regard to their contribution to cooked beef toughness.

The Role of the Lysyl Oxidases in Tissue Repair and Remodeling: A Concise Review

Tissue injury provokes a series of events containing inflammation, new tissue formation and tissue remodeling which are regulated by the spatially and temporally coordinated organization. It is an evolutionarily conserved, multi-cellular, multi-molecular process via complex signalling network. Tissue injury disorders present grievous clinical problems and are likely to increase since they are generally associated with the prevailing diseases such as diabetes, hypertension and obesity. Although these dynamic responses vary not only for the different types of trauma but also for the different organs, a balancing act between the tissue degradation and tissue synthesis is the same. In this process, the degradation of old extracellular matrix (ECM) elements and new ones' synthesis and deposition play an essential role, especially collagens. Lysyl oxidase (LOX) and four lysyl oxidase-like proteins are a group of enzymes capable of catalyzing cross-linking reaction of collagen and elastin, thus initiating the formation of covalent cross-links that insolubilize ECM proteins. In this way, LOX facilitates ECM stabilization through ECM formation, development, maturation and remodeling. This ability determines its potential role in tissue repair and regeneration. In this review, based on the current in vitro, animal and human in vivo studies which have shown the significant role of the LOXs in tissue repair, e.g., tendon regeneration, ligament healing, cutaneous wound healing, and cartilage remodeling, we focused on the role of the LOXs in inflammation phase, proliferation phase, and tissue remodeling phase of the repair process. By summarizing its healing role, we hope to shed light on the understanding of its potential in tissue repair and provide up to date therapeutic strategies towards related injuries.

Immunoexpression of IGF1, IGF2, and osteopontin in craniofacial bone repair associated with autogenous grafting in rat models treated with alendronate sodium

OBJECTIVES

The aim of this study was to verify the likely influence of presurgical administration of low doses of alendronate sodium in craniofacial bone repair and correlate the histological frame found on reparative tissue to the immunohistochemical presence of IGF1, IGF2, and osteopontin (OP).

MATERIALS AND METHODS

In total, 120 rats were randomly allocated into four groups: group C (control), group OA (autogenous bone), group B (bisphosphonates), and group OA-B (autogenous bone + bisphosphonates). Groups B and OA-B received alendronate sodium (ALN) 0.01 mg/kg subcutaneously on alternate days for 4 weeks. Groups C and OA received saline solution. Critical 5-mm defects were created in rat calvaria, which were filled with blood clot in groups C and B and with autogenous bone in groups OA and OA-B. The animals were euthanized at 15 or 30 days postoperatively. Histological analysis and immunohistochemistry of IGF1, IGF2, and OP proteins was performed. Immunohistochemistry evaluated the expression in cells and extracellular matrix.

RESULTS

Groups C and B revealed healing predominantly characterized by connective tissue. In groups OA and OA-B, healing of connective tissue and neoformation of compact bone was observed. Expression of IGF1 an OP was present in all specimens. IGF1 expression in cells was more pronounced in groups OA and OA-B 15 days postoperatively. The expression of IGF2 was only observed in groups OA and OA-B, with greater intensity in group OA-B 30 days postoperatively. OP expression was only observed in cells and not in the extracellular matrix and was more pronounced in group OA 15 days postoperatively.

CONCLUSIONS

The application of systemic ALN at a dose of 0.01 mg/kg did not improve cranial bone matrix deposition. Nevertheless, the expression of IGF1 and OP and a slight marking of IGF2 were observed especially in groups OA and OA-B in the wound healing process. Future studies should assess higher doses of ALN to verify its influence on bone repair.

CLINICAL RELEVANCE

The systemic use of ALN 0.01 mg/kg on alternate days 4 weeks prior to surgery did not interfere with bone repair.

Insulin-like growth factor 1, glycation and bone fragility: implications for fracture resistance of bone

Despite our extensive knowledge of insulin-like growth factor 1 (IGF1) action on the growing skeleton, its role in skeletal homeostasis during aging and age-related development of certain diseases is still unclear. Advanced glycation end products (AGEs) derived from glucose are implicated in osteoporosis and a number of diabetic complications. We hypothesized that because in humans and rodents IGF1 stimulates uptake of glucose (a glycation substrate) from the bloodstream in a dose-dependent manner, the decline of IGF1 could be associated with the accumulation of glycation products and the decreasing resistance of bone to fracture. To test the aforementioned hypotheses, we used human tibial posterior cortex bone samples to perform biochemical (measurement of IGF1, fluorescent AGEs and pentosidine (PEN) contents) and mechanical tests (crack initiation and propagation using compact tension specimens). Our results for the first time show a significant, age-independent association between the levels of IGF1 and AGEs. Furthermore, AGEs (fAGEs, PEN) predict propensity of bone to fracture (initiation and propagation) independently of age in human cortical bone. Based on these results we propose a model of IGF1-based regulation of bone fracture. Because IGF1 level increases postnatally up to the juvenile developmental phase and decreases thereafter with aging, we propose that IGF1 may play a protective role in young skeleton and its age-related decline leads to bone fragility and an increased fracture risk. Our results may also have important implications for current understanding of osteoporosis- and diabetes-related bone fragility as well as in the development of new diagnostic tools to screen for fragile bones.

Diabetes, collagen, and bone quality

Diabetes increases risk of fracture, although type 2 diabetes is characterized by normal or high bone mineral density (BMD) compared with the patients without diabetes. The fracture risk of type 1 diabetes as well as type 2 diabetes increases beyond an explained by a decrease of BMD. Thus, diabetes may reduce bone strength without change in BMD. Whole bone strength is determined by bone density, structure, and quality, which encompass the micro-structural and tissue material properties. Recent literature showed that diabetes reduces bone material properties rather than BMD. Collagen intermolecular cross-linking plays an important role in the expression of bone strength. Collagen cross-links can be divided into beneficial enzymatic immature divalent and mature trivalent cross-links and disadvantageous nonenzymatic cross-links (Advanced glycation end products: AGEs) induced by glycation and oxidation. The formation pathway and biological function are quite different. Not only hyperglycemia, but also oxidative stress induces the reduction in enzymatic cross-links and the formation of AGEs. In this review, we describe the mechanism of low bone quality in diabetes and the usefulness of the measurement of plasma or urinary level of AGEs for estimation of fracture risk.

Muscle and tendon connective tissue adaptation to unloading, exercise and NSAID

The extracellular matrix network of skeletal muscle and tendon connective tissue is primarily composed of collagen and connects the muscle contractile protein to the bones in the human body. The mechanical properties of the connective tissue are important for the effectiveness of which the muscle force is transformed into movement. Periods of unloading and exercise affect the synthesis rate of connective tissue collagen protein, whereas only sparse information exits regarding collagen protein degradation. It is likely, though, that changes in both collagen protein synthesis and degradation are required for remodeling of the connective tissue internal structure that ultimately results in altered mechanical properties of the connective tissue. Both unloading and exercise lead to increased production of growth factors and inflammatory mediators that are involved in connective tissue remodeling. Despite the fact that non-steroidal anti-inflammatory drugs seem to inhibit the healing process of connective tissue and the stimulating effect of exercise on connective tissue protein synthesis, these drugs are often consumed in relation to connective tissue injury and soreness. However, the potential effect of non-steroidal anti-inflammatory drugs on connective tissue needs further investigation.

Effect of growth hormone on aging connective tissue in muscle and tendon: gene expression, morphology, and function following immobilization and rehabilitation

It is unknown whether loss in musculotendinous tissue during inactivity can be counteracted by growth hormone (GH), and whether GH accelerate rehabilitation in aging individuals. Elderly men (65–75 yr; n = 12) had one leg immobilized 2 wk followed by 6 wk of retraining and were randomly assigned to daily injections of recombinant GH (rhGH; n = 6) or placebo (Plc; n = 6). Cross-sectional area (CSA), muscle strength (MVC), and biomechanical properties of m. quadriceps and patellar tendon were determined. Muscle and tendon biopsies were analyzed for gene expressions (mRNA) of collagen (COL1A1/3A1) and insulin-like growth factors (IGF-1Ea/Ec). Fibril morphology was analyzed by transmission electron microscope (TEM). In tendon, CSA and biomechanical properties did not change following immobilization, but an increase in CSA was found after 6 wk of rehabilitation in both groups. The changes were more pronounced when GH was injected. Furthermore, tendon stiffness increased in the GH group. Muscle CSA declined after immobilization in the Plc but not in the GH group. Muscle CSA increased during retraining, with a significantly larger increase in the GH group compared with the Plc group. Both a time and a group effect were seen for IGF-1Ea/Ec and COL1A1/3A1 mRNA expression in muscle, with a difference between GH and Plc. IGF-1Ea/Ec and COL-1A1/3A1 mRNA expression increased in muscle following immobilization and retraining in subjects receiving GH, whereas an increase in IGF-1Ec mRNA expression was seen in the Plc group only after retraining. In conclusion, in elderly humans, GH seems to have a matrix stabilizing effect during inactivity and rehabilitation by stimulating collagen expression in the musculotendinous tissue and increasing tendon CSA and stiffness.

Tendon and skeletal muscle matrix gene expression and functional responses to immobilisation and rehabilitation in young males: effect of growth hormone administration

We examined the effect of growth hormone (GH) on connective tissue of tendon and skeletal muscle during immobilisation and re-training in humans. Young men (20-30 years; n = 20) were randomly assigned to daily recombinant human GH (rhGH) (33-50 μg kg(-1) day(-1)) or placebo (Plc), and had one leg immobilised for 2 weeks, followed by 6 weeks of strength training. The cross-sectional area (CSA), maximal muscle strength (maximal voluntary contraction, MVC) and biomechanical properties of the quadriceps muscle and patellar tendon were determined. Muscle and tendon biopsies were analysed for mRNA of collagen (COL1A1/3A1), insulin-like growth factors (IGF-1Ea/Ec), lysyl oxidase (LOX), matrix metalloproteases (MMP-2 and MMP-9), decorin and tenascin-C. Fibril morphology was analysed by transmission electron microscopy (TEM) to detect changes in the fibril diameter distribution. In muscle, CSA and MVC declined with immobilisation and recovered with rehabilitation similarly in both groups. Likewise, both groups showed increased IGF-1Ea/Ec and COL1A1/3A1 expression in muscle during re-training after immobilisation compared with baseline, and the increase was more pronounced when subjects received GH. The tendon CSA did not change during immobilisation, but increased in both groups during 6 weeks of rehabilitation (∼14%). A decline in tendon stiffness after immobilisation was observed only in the Plc group, and an increase during 6 weeks of rehabilitation was observed only in the GH group. IGF-1Ea and COL1A1/3A1 mRNA increased with immobilisation in the GH group only, and LOX mRNA was higher in the GH group than in the Plc group after immobilisation. Both groups showed an increase in MMP-2 with immobilisation, whereas no changes in MMP-9, decorin and tenascin-C were observed. The tendon fibril diameter distribution remained unchanged in both groups. In conclusion, GH stimulates collagen expression in both skeletal muscle and tendon, abolishes the normal inactivity-related decline in tendon stiffness and LOX, and results in increased tendon CSA and stiffness during rehabilitation. GH has a matrix-stabilising effect during periods of inactivity and rehabilitation in humans.

Bone quality in diabetes

Diabetes is associated with increased risk of fracture, although type 2 diabetes is characterized by normal bone mineral density (BMD). The fracture risk of type 1 diabetes increases beyond an explained by a decrease of BMD. Thus, diabetes may be associated with a reduction of bone strength that is not reflected in the measurement of BMD. Based on the present definition, both bone density and quality, which encompass the structural and material properties of bone, are important factors in the determination of bone strength. Diabetes reduces bone quality rather than BMD. Collagen cross-linking plays an important role in bone strength. Collagen cross-links can be divided into lysyl hydroxylase and lysyl oxidase-mediated enzymatic immature divalent cross-links, mature trivalent cross-links, and glycation- or oxidation-induced non-enzymatic cross-links (Advanced Glycation End-products: AGEs) such as pentosidine. These types of cross-links differ in the mechanism of formation and in function. Not only hyperglycemia, but also oxidative stress induces the reduction in enzymatic beneficial cross-links and the accumulation of disadvantageous AGEs in bone. In this review, we describe the mechanism of low bone quality in diabetes.

The contribution of collagen crosslinks to bone strength

Collagen crosslinking is a major post-translational modification of collagen which has important roles in determining the biomechanical competence of bone. Crosslinks can be divided into enzymatic lysil oxidase-mediated and non-enzymatic glycation-induced (advanced glycation end products, AGE) molecules. In addition, collagen in bone can also undergo spontaneous isomerization and racemization of the aspartic acid residues with the C-telopeptide (CTX), leading to the formation of two isomers namely α (newly formed collagen) and β (matured isomerized collagen) CTX. Several in vitro and ex vivo studies, relating the bone content of these crosslinks with bone strength, have shown that they contributed to the mechanical competence of trabecular and cortical bone-mainly on the post-yield properties-in part independent of the bone mineral content. In addition, AGEs such as pentosidine have been reported to alter the formation and propagation of microdamage by making the bone more brittle. The bone content of AGEs and isomerization can also be modified by antiresorptive and anabolic therapies. They may thus explain part of the antifracture efficacy of these treatments. The main challenge consists in the transposition of these in vitro/ex vivo studies to clinical applications for the development of a non-invasive biomarker, as none of currently identified collagen crosslinks (both enzymatic and nonenzymatic) is bone specific. Nevertheless, serum or urine levels of pentosidine and the ratio of α/β CTX have been reported to predict fracture risk in postmenopausal women, in men and in patients with type 2 diabetes.

Changes in the contents of enzymatic immature, mature, and non-enzymatic senescent cross-links of collagen after once-weekly treatment with human parathyroid hormone (1-34) for 18 months contribute to improvement of bone strength in ovariectomized monkeys

Improvements in total content of enzymatic cross-linking, the ratio of hydroxylysine-derived enzymatic cross-links, and non-enzymatic advanced glycation end product cross-link formation from once-weekly administration of hPTH(1-34) for 18 months in OVX cynomolgus monkeys contributed to the improvement of bone strength.

INTRODUCTION

Parathyroid hormone (PTH) is used for the treatment of osteoporosis. To elucidate the contribution of material properties to bone strength after once-weekly treatment with hPTH(1-34) in an ovariectomized (OVX) primate model, the content of collagen and enzymatic immature, mature, and non-enzymatic cross-links, collagen maturity, trabecular architecture, and mineralization in vertebrae were simultaneously estimated.

METHODS

Adult female cynomolgus monkeys were divided into four groups (n = 18-20 each) as follows: SHAM group, OVX group, and OVX monkeys given once-weekly subcutaneous injections of hPTH(1-34) either at 1.2 or 6.0 μg/kg (low- or high-PTH groups) for 18 months. The content of collagen, enzymatic and non-enzymatic cross-linking pentosidine, collagen maturity, trabecular architecture, mineralization, and cancellous bone strength of vertebrae were analyzed.

RESULTS

Low-PTH and high-hPTH treatments increased the content of enzymatic immature and mature cross-links, bone volume (BV/TV), and trabecular thickness, and decreased pentosidine, compared with the OVX group. Stepwise logistic regression analysis revealed that BV/TV, the content of total enzymatic cross-links, and calcium content independently affected ultimate load (model R (2) = 0.748, p < 0.001) and breaking energy (model R (2) = 0.702, p < 0.001). BV/TV was the most powerful and enzymatic cross-link content was the second powerful determinant of both ultimate load and breaking energy. The most powerful determinant of stiffness was the enzymatic cross-link content (model R (2) = 0.270, p < 0.001).

CONCLUSION

Once-weekly preventive administration of hPTH(1-34) increased the total contents of immature and mature enzymatic cross-links, which contributed significantly to vertebral cancellous bone strength.

Effects of alfacalcidol on mechanical properties and collagen cross-links of the femoral diaphysis in glucocorticoid-treated rats

Bone fragility is increased in glucocorticoid (GC)-induced osteopenia even though GC-treated patients have higher bone mineral density (BMD), suggesting that the impaired bone quality may affect bone strength. This study was conducted to clarify the effects of GC on bone strength and collagen cross-links of adult rats and the effect of coadministration of alfacalcidol (ALF), a prodrug of active vitamin D(3). Six-month-old male Wistar-Imamichi rats (n = 32) were divided into the following four groups with equal average body weight: (1) 4-week age-matched controls, (2) 4-week GC (prednisolone, 10 mg/kg daily, i.m.) with concomitant administration of vehicle, (3) 4-week GC with concomitant administration of ALF (0.05 μg/kg daily, p.o.), and (4) 4-week GC with concomitant administration of ALF (0.1 μg/kg daily, p.o.). At the end of treatment, BMD, collagen cross-links, mechanical properties of the femoral midshaft, bone metabolic markers, and biochemical parameters were analyzed. In the GC group, femoral bone strength decreased without any change of BMD. This was accompanied by a decrease in the content of enzymatic cross-links. ALF (0.1 μg/kg) inhibited the GC-induced reduction in bone strength. The content of mature cross-links in the 0.1-μg/kg ALF group was significantly higher than that in the GC group. GC treatment caused a decrease in bone metabolic markers and serum calcium levels, which was counteracted by ALF coadministration. Preventive treatment with ALF inhibited the deterioration of bone mechanical properties primarily in association with the restoration of enzymatic cross-link formation and amelioration of the adverse effects of GC treatment on calcium metabolism.

Collagen cross-links as a determinant of bone quality: a possible explanation for bone fragility in aging, osteoporosis, and diabetes mellitus

Collagen cross-linking, a major post-translational modification of collagen, plays important roles in the biological and biomechanical features of bone. Collagen cross-links can be divided into lysyl hydroxylase and lysyloxidase-mediated enzymatic immature divalent cross-links,mature trivalent pyridinoline and pyrrole cross-links, and glycation- or oxidation-induced non-enzymatic cross-links(advanced glycation end products) such as glucosepane and pentosidine. These types of cross-links differ in the mechanism of formation and in function. Material properties of newly synthesized collagen matrix may differ in tissue maturity and senescence from older matrix in terms of crosslink formation. Additionally, newly synthesized matrix in osteoporotic patients or diabetic patients may not necessarily be as well-made as age-matched healthy subjects. Data have accumulated that collagen cross-link formation affects not only the mineralization process but also microdamage formation. Consequently, collagen cross-linking is thought to affect the mechanical properties of bone. Furthermore,recent basic and clinical investigations of collagen cross-links seem to face a new era. For instance, serum or urine pentosidine levels are now being used to estimate future fracture risk in osteoporosis and diabetes. In this review, we describe age-related changes in collagen cross-links in bone and abnormalities of cross-links in osteoporosis and diabetes that have been reported in the literature.

Characteristics of the aortic elastic network and related phenotypes in seven inbred rat strains

Extracellular matrix (ECM) molecules such as elastin and collagen provide mechanical support to the vessel wall and are essential for vascular function. Evidence that genetic factors influence aortic ECM composition and organization was concluded from our previous studies showing that the inbred Brown Norway (BN) rat differs significantly from the outbred Long-Evans (LE) and the inbred LOU rat with respect to both thoracic aortic elastin content and internal elastic lamina (IEL) rupture in the abdominal aorta and iliac arteries. Here, we measured aortic elastin and collagen contents as well as factors that may modulate these parameters [insulin growth factor (IGF)-I, transforming growth factor (TGF)-beta(1), and matrix metalloproteinase (MMP)-2] in seven inbred rat strains, including BN and LOU. We also investigated whether IEL ruptures occur in strains other than BN. We showed that LOU, LE, BN, and Fischer 344 (F344) rats were significantly different for aortic elastin content and elastin-to-collagen ratio, whereas LE, Lewis, WAG, and Wistar-Furth (WF) were similar for these parameters. BN and F344 had the lowest values. BN was the only strain to present numerous IEL ruptures, whereas F344, LE, and WF presented a few and the other strains presented none. In addition, IGF-I and TGF-beta(1) levels in the plasma and aorta differed significantly between strains, suggesting genetic control of their production. Because inbred rat strains provide interesting models for quantitative trait locus analysis, our results concerning elastin, collagen, IEL ruptures, and cytokines may provide a basis for the search for candidate genes involved in the control of these phenotypes.

Diet effects on weight gain and body composition in high growth (hg/hg) mice

Nongenetic factors such as nutrition modulate the effects of genes responsible for overgrowth in animals. The goal of this study was to examine the importance of genotype x diet interactions on the effects of a major locus that regulates growth in the mouse. We have examined the phenotype of high growth (hg), a partially recessive autosomal locus that increases growth rate and mature body size. C57BL/6J (C57) and congenic C57BL/6J-hg/hg (HG) mice were fed three experimental diets differing in protein and energy content from 3 to 12 wk of age. HG mice grew faster and were, on average, 51% heavier than C57 at 12 wk of age. Feed intake was higher in HG mice but proportional to the increase in body weight. The magnitude of the differences in body size and composition between lines depended on the interaction between genotype and the protein/energy ratio of the diet. In C57, the diets modified the level of fatness without changing adult lean mass. However, in HG the diets differentially affected both linear growth and body composition. In general, HG had higher plasma levels of insulin-like growth factor I at 3 and 12 wk than C57. Plasma insulin did not differ between lines, but leptin was higher for C57 mice fed a high-energy diet. These results show that the effects of hg on growth are modulated by diet composition. Therefore, this mutation could be a valuable model with which to study the genetic and nutritional aspects of overgrowth disorders.

Changes in growth factor expression in the ageing prostate may disrupt epithelial-stromal homeostasis

The alterations in expression of six growth factors known to be regulators of prostatic function have been examined in the ventral lobe of prostates from young adult (14 week) and ageing (1.5 year) Wistar rats. The selected growth factors were transforming growth factor beta (TGFbeta1), insulin-like growth factor I (IGF-I), insulin-like growth factor II (IGF-II), platelet derived growth factor (PDGF), basic fibroblast growth factor (FGF2) and epidermal growth factor (EGF). The extracellular matrix growth co-factor thrombospondin (TSP) was also examined. Our study demonstrated a 2.9-fold up-regulation of TGFbeta1 (p < 0.0001), a 2.0-fold increase in FGF2 (p < 0.0002), an 8.3-fold increase in IGF-II (p < 0.0007) and a 5.4-fold increase in EGF (p < 0.0001) in ageing compared to adult prostate tissue. Conversely, we observed a 2.7-fold down-regulation of IGF-I (p < 0.0005), a 1.7-fold decrease in PDGF (p < 0.0097) and a 5.8-fold decrease in TSP (p < 0.0079) in ageing rat prostate tissue. The observed alterations in growth factor expression in this study may be the result or cause of, an imbalance in the proliferative-apoptotic balance during ageing. This imbalance may explain the increase in epithelial proliferation that is characteristic of the normal ageing prostate. As in other systems it seems likely that these factors work synergistically rather than in isolation.