Sequences of liver cDNAs encoding two different mouse insulin-like growth factor I precursors

The role of mechano growth factor in chondrocytes and cartilage defects: a concise review

Mechano growth factor (MGF), an isoform of insulin-like growth factor 1 (IGF-1), is recognized as a typical mechanically sensitive growth factor and has been shown to play an indispensable role in the skeletal system. In the joint cavity, MGF is highly expressed in chondrocytes, especially in the damaged cartilage tissue caused by trauma or degenerative diseases such as osteoarthritis (OA). Cartilage is an extremely important component of joints because it functions as a shock absorber and load distributer at the weight-bearing interfaces in the joint cavity, but it can hardly be repaired once injured due to its lack of blood vessels, lymphatic vessels, and nerves. MGF has been proven to play an important role in chondrocyte cell behaviors, including cell proliferation, migration, differentiation, inflammatory reactions and apoptosis, in and around the injury site. Moreover, under the normalized mechanical microenvironment in the joint cavity, MGF can sense and respond to mechanical stimuli, regulate chondrocyte activity, and maintain the homeostasis of cartilage tissue. Recent reports continue to explain its effects on various cell types and sport-related tissues, but its role in cartilage development, homeostasis and disease occurrence is still controversial, and its internal biological mechanism is still elusive. In this review, we summarize recent discoveries in the role of MGF in chondrocytes and cartilage defects, including tissue repair at the macroscopic level and chondrocyte activities at the microcosmic level, and discuss the current state of research and potential gaps in knowledge.

Periosteal topology creates an osteo-friendly microenvironment for progenitor cells

The periosteum on the skeletal surface creates a unique micro-environment for cortical bone homeostasis, but how this micro-environment is formed remains a mystery. In our study, we observed the cells in the periosteum presented elongated spindle-like morphology within the aligned collagen fibers, which is in accordance with the differentiated osteoblasts lining on the cortical surface. We planted the bone marrow stromal cells(BMSCs), the regular shaped progenitor cells, on collagen-coated aligned fibers, presenting similar cell morphology as observed in the natural periosteum. The aligned collagen topology induced the elongation of BMSCs, whichfacilitated the osteogenic process. Transcriptome analysis suggested the aligned collagen induced the regular shaped cells to present part of the periosteum derived stromal cells(PDSCs) characteristics by showing close correlation of the two cell populations. In addition, the elevated expression of PDSCs markers in the cells grown on the aligned collagen-coated fibers further indicated the function of periosteal topology in manipulating cells' behavior. Enrichment analysis revealed cell-extracellular matrix interaction was the major pathway initiating this process, which created an osteo-friendly micro-environment as well. At last, we found the aligned topology of collagen induced mechano-growth factor expression as the result of Igf1 alternative splicing, guiding the progenitor cells behavior and osteogenic process in the periosteum. This study uncovers the key role of the aligned topology of collagen in the periosteum and explains the mechanism in creating the periosteal micro-environment, which gives the inspiration for artificial periosteum design.

Immunohistochemical expression of insulin-like growth factor-1Ec in primary endometrial carcinoma: Association with PTEN, p53 and survivin expression

Chronic hyperinsulinemia due to insulin resistance and elevated levels of insulin-like growth factor (IGF)-1 and IGF-2 are suggestive of a significantly higher risk of endometrial carcinoma. There is a wealth of evidence showing differential expression of IGF-1 isoforms in various types of cancer. In the present study, 99 archived endometrial carcinoma tissue sections were retrospectively assessed by immunohistochemistry for IGF-1Ec isoform expression. Expression of IGF-1Ec was also assessed in nine cases of non-neoplastic endometrial tissue adjacent to the tumor, in 30 cases with normal endometrium and in 30 cases with endometrial hyperplasia. Furthermore, the association between IGF-1Ec and the concurrent expression of phosphatase and tensin homologue deleted on chromosome 10 (PTEN), p53 or survivin was assessed, as well as their combined expression in association with clinicopathological variables. In endometrial carcinoma, IGF-1Ec expression was high in non-endometrioid carcinoma (serous papillary or clear cell carcinoma) compared with that in endometrioid adenocarcinoma. IGF-1Ec expression was also high in the presence of tumoral necrosis. Furthermore, there was a significant correlation between the histological differentiation and the sum of staining intensity and the number of IGF-1Ec immunopositive cells in endometrial carcinoma. There was a moderate negative correlation between co-expression of IGF-1Ec and PTEN, for both the number of immunopositive cells (P=0.006, ρ=−0.343) and the sum of staining (scores and intensity; P=0.006, ρ=−0.343). Furthermore, there was a positive correlation between the sum of staining (scores and intensity) and co-expression of IGF-1Ec and survivin (P=0.043, ρ=0.225). However, there was no association between concomitant expression of IGF-1Ec and p53. These results emphasized the importance of IGF-1Ec expression during development of non-estrogen dependent endometrial adenocarcinoma. IGF-1Ec and PTEN may function opposingly during endometrial carcinogenesis. By contrast, IGF-1Ec and survivin may share common molecular pathways and may promote, in parallel, tumoral development.

Role of Alternatively Spliced Messenger RNA (mRNA) Isoforms of the Insulin-Like Growth Factor 1 (IGF1) in Selected Human Tumors

Insulin-like growth factor 1 (IGF1) is a key regulator of tissue growth and development that is also implicated in the initiation and progression of various cancers. The human IGF1 gene contains six exons and five long introns, the transcription of which is controlled by two promoters (P1 and P2). Alternate promoter usage, as well as alternative splicing (AS) of IGF1, results in the expression of six various variants (isoforms) of mRNA, i.e., IA, IB, IC, IIA, IIB, and IIC. A mature 70-kDa IGF1 protein is coded only by exons 3 and 4, while exons 5 and 6 are alternatively spliced code for the three C-terminal E peptides: Ea (exon 6), Eb (exon 5), and Ec (fragments of exons 5 and 6). The most abundant of those transcripts is IGF1Ea, followed by IGF1Eb and IGF1Ec (also known as mechano-growth factor, MGF). The presence of different IGF1 transcripts suggests tissue-specific auto- and/or paracrine action, as well as separate regulation of both of these gene promoters. In physiology, the role of different IGF1 mRNA isoforms and pro-peptides is best recognized in skeletal muscle tissue. Their functions include the development and regeneration of muscles, as well as maintenance of proper muscle mass. In turn, in nervous tissue, a neuroprotective function of short peptides, produced as a result of IGF1 expression and characterized by significant blood-brain barrier penetrance, has been described and could be a potential therapeutic target. When it comes to the regulation of carcinogenesis, the potential biological role of different var iants of IGF1 mRNAs and pro-peptides is also intensively studied. This review highlights the role of IGF1 isoform expression (mRNAs, proteins) in physiology and different types of human tumors (e.g., breast cancer, cervical cancer, colorectal cancer, osteosarcoma, prostate and thyroid cancers), as well as mechanisms of IGF1 spliced variants involvement in tumor biology.

Insulin-Like Growth Factor I Regulation and Its Actions in Skeletal Muscle

The insulin-like growth factor (IGF) pathway is essential for promoting growth and survival of virtually all tissues. It bears high homology to its related protein insulin, and as such, there is an interplay between these molecules with regard to their anabolic and metabolic functions. Skeletal muscle produces a significant proportion of IGF-1, and is highly responsive to its actions, including increased muscle mass and improved regenerative capacity. In this overview, the regulation of IGF-1 production, stability, and activity in skeletal muscle will be described. Second, the physiological significance of the forms of IGF-1 produced will be discussed. Last, the interaction of IGF-1 with other pathways will be addressed. © 2019 American Physiological Society. Compr Physiol 9:413-438, 2019.

Changes in Skeletal Muscle and Body Weight on Sleeping Beauty Transposon-Mediated Transgenic Mice Overexpressing Pig mIGF-1

Insulin-like growth factor (IGF-I) is an important growth factor in mammals, but the functions of the local muscle-specific isoform of insulin-like growth factor 1 (mIGF-1) to skeletal muscle development have rarely been reported. To determine the effect of pig mIGF-1 on body development and muscle deposition in vivo and to investigate the molecular mechanisms, the transgenic mouse model was generated which can also provide experimental data for making transgenic pigs with pig endogenous IGF1 gene. We constructed a skeletal muscle-specific expression vector using 5′- and 3′-regulatory regions of porcine skeletal α-actin gene. The expression cassette was flanked with Sleeping Beauty transposon (SB)-inverted terminal repeats. The recombinant vector could strongly drive enhanced green fluorescence protein (EGFP) reporter gene expression specifically in mouse myoblast cells and porcine fetal fibroblast cells, but not in porcine kidney cells. The EGFP level driven by α-actin regulators was significantly stronger than that driven by cytomegalovirus promoters. These results indicated that the cloned α-actin regulators could effectively drive specific expression of foreign genes in myoblasts, and the skeletal muscle-specific expression vector mediated with SB transposon was successfully constructed. To validate the effect of pig mIGF-1 on skeletal muscle growth, transgenic mice were generated by pronuclear microinjection of SB-mediated mIGF-1 skeletal expression vector and SB transposase-expressing plasmid. The transgene-positive rates of founder mice and the next-generation F1 mice were 30% (54/180) and 90.1% (64/71), respectively. The mIGF-1 gene could be expressed in skeletal muscle specifically. The levels of mRNA and protein in transgenic mice were 15 and 3.5 times higher, respectively, than in wild-type mice. The body weights of F1 transgenic mice were significantly heavier than wild-type mice from the age of 8 weeks onwards. The paraffin-embedded sections of gastrocnemius from 16-week-old transgenic male mice showed that the numbers of myofibers per unit were increased in comparison with those in the wild-type mice. mIGF-1 overexpression in mice skeletal muscle may promote myofibers hypertrophy and muscle production, and increased the average body weight of adult mice. Transgenic mice models can be generated by the mediation of SB transposon with high transgene efficiency.

Human IGF-I propeptide A promotes articular chondrocyte biosynthesis and employs glycosylation-dependent heparin binding

BACKGROUND

Insulin-like growth factor I (IGF-I) is a key regulator of chondrogenesis, but its therapeutic application to articular cartilage damage is limited by rapid elimination from the repair site. The human IGF-I gene gives rise to three IGF-I propeptides (proIGF-IA, proIGF-IB and proIGF-IC) that are cleaved to create mature IGF-I. In this study, we elucidate the processing of IGF-I precursors by articular chondrocytes, and test the hypotheses that proIGF-I isoforms bind to heparin and regulate articular chondrocyte biosynthesis.

METHODS

Human IGF-I propeptides and mutants were overexpressed in bovine articular chondrocytes. IGF-I products were characterized by ELISA, western blot and FPLC using a heparin column. The biosynthetic activity of IGF-I products on articular chondrocytes was assayed for DNA and glycosaminoglycan that the cells produced.

RESULTS

Secreted IGF-I propeptides stimulated articular chondrocyte biosynthetic activity to the same degree as mature IGF-I. Of the three IGF-I propeptides, only one, proIGF-IA, strongly bound to heparin. Interestingly, heparin binding of proIGF-IA depended on N-glycosylation at Asn92 in the EA peptide. To our knowledge, this is the first demonstration that N-glycosylation determines the binding of a heparin-binding protein to heparin.

CONCLUSION

The biosynthetic and heparin binding abilities of proIGF-IA, coupled with its generation of IGF-I, suggest that proIGF-IA may have therapeutic value for articular cartilage repair.

GENERAL SIGNIFICANCE

These data identify human pro-insulin-like growth factor IA as a bifunctional protein. Its combined ability to bind heparin and augment chondrocyte biosynthesis makes it a promising therapeutic agent for cartilage damage due to trauma and osteoarthritis.

GH/IGF-1 Signaling and Current Knowledge of Epigenetics; a Review and Considerations on Possible Therapeutic Options

Epigenetic mechanisms play an important role in the regulation of the Growth Hormone- Insulin-like Growth Factor 1 (GH-IGF1) axis and in processes for controlling long bone growth, and carbohydrate and lipid metabolism. Improvement of methodologies that allow for the assessment of epigenetic regulation have contributed enormously to the understanding of GH action, but many questions still remain to be clarified. The reversible nature of epigenetic factors and, particularly, their role as mediators between the genome and the environment, make them viable therapeutic target candidates. Rather than reviewing the molecular and epigenetic pathways regulated by GH action, in this review we have focused on the use of epigenetic modulators as potential drugs to improve the GH response. We first discuss recent progress in the understanding of intracellular molecular mechanisms controlling GH and IGF-I action. We then emphasize current advances in genetic and epigenetic mechanisms that control gene expression, and which support a key role for epigenetic regulation in the cascade of intracellular events that trigger GH action when coupled to its receptor. Thirdly, we focus on fetal programming and epigenetic regulation at the IGF1 locus. We then discuss epigenetic alterations in intrauterine growth retardation, and the possibility for a potential epigenetic pharmaceutical approach in short stature associated with this fetal condition. Lastly, we review an example of epigenetic therapeutics in the context of growth-related epigenetic deregulation disorders. The advance of our understanding of epigenetic changes and the impact they are having on new forms of therapy creates exciting prospects for the future.

Cardiac-Restricted IGF-1Ea Overexpression Reduces the Early Accumulation of Inflammatory Myeloid Cells and Mediates Expression of Extracellular Matrix Remodelling Genes after Myocardial Infarction

Strategies to limit damage and improve repair after myocardial infarct remain a major therapeutic goal in cardiology. Our previous studies have shown that constitutive expression of a locally acting insulin-like growth factor-1 Ea (IGF-1Ea) propeptide promotes functional restoration after cardiac injury associated with decreased scar formation. In the current study, we investigated the underlying molecular and cellular mechanisms behind the enhanced functional recovery. We observed improved cardiac function in mice overexpressing cardiac-specific IGF-1Ea as early as day 7 after myocardial infarction. Analysis of gene transcription revealed that supplemental IGF-1Ea regulated expression of key metalloproteinases (MMP-2 and MMP-9), their inhibitors (TIMP-1 and TIMP-2), and collagen types (Col 1α1 and Col 1α3) in the first week after injury. Infiltration of inflammatory cells, which direct the remodelling process, was also altered; in particular there was a notable reduction in inflammatory Ly6C+ monocytes at day 3 and an increase in anti-inflammatory CD206+ macrophages at day 7. Taken together, these results indicate that the IGF-1Ea transgene shifts the balance of innate immune cell populations early after infarction, favouring a reduction in inflammatory myeloid cells. This correlates with reduced extracellular matrix remodelling and changes in collagen composition that may confer enhanced scar elasticity and improved cardiac function.

Insulin-like growth factor 1 increases apical fibronectin in blastocysts to increase blastocyst attachment to endometrial epithelial cells in vitro

STUDY QUESTION

Does insulin-like growth factor 1 (IGF1) increase adhesion competency of blastocysts to increase attachment to uterine epithelial cells in vitro?

SUMMARY ANSWER

IGF1 increases apical fibronectin on blastocysts to increase attachment and invasion in an in vitro model of implantation.

WHAT IS KNOWN ALREADY

Fibronectin integrin interactions are important in attachment of blastocysts to uterine epithelial cells at implantation.

STUDY DESIGN, SIZE, DURATION

Mouse blastocysts (hatched or near completion of hatching) were cultured in serum starved (SS) medium with varying treatments for 24, 48 or 72 h. Treatments included 10 ng/ml IGF1 in the presence or absence of the PI3 kinase inhibitor LY294002, an IGF1 receptor (IGF1R) neutralizing antibody or fibronectin. Effects of treatments on blastocysts were measured by attachment of blastocysts to Ishikawa cells, blastocyst outgrowth and fibronectin and focal adhesion kinase (FAK) localization and expression. Blastocysts were randomly allocated into control and treatment groups and experiments were repeated a minimum of three times with varying numbers of blastocysts used in each experiment. FAK and integrin protein expression on Ishikawa cells was quantified in the presence or absence of IGF1.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Fibronectin expression and localization in blastocysts was studied using immunofluorescence and confocal microscopy. Global surface expression of integrin αvβ3, β3 and β1 was measured in Ishikawa cells using flow cytometry. Expression levels of phosphorylated FAK and total FAK were measured in Ishikawa cells and blastocysts by western blot and image J analysis. Blastocyst outgrowth was quantified using image J analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

The presence of IGF1 significantly increased mouse blastocyst attachment to Ishikawa cells compared with SS conditions (P < 0.01). IGF1 treatment resulted in distinct apical fibronectin staining on blastocysts, which was reduced by the PI3 kinase inhibitor LY294002. This coincided with a significant increase in blastocyst outgrowth in the presence of IGF1 (P < 0.01) or fibronectin (P < 0.001), which was abolished by LY294002 (P < 0.001). Apical expression of integrin αvβ3, β3 and β1 in Ishikawa cells was unaltered by IGF1. However, IGF1 increased phosphorylated FAK (P < 0.05) and total FAK expression in Ishikawa cells. FAK signalling is linked to integrin activation and can affect the integrins' ability to bind and recognize extracellular matrix proteins such as fibronectin. Treatment of blastocysts with IGF1 before co-culture with Ishikawa cells increased their attachment (P < 0.05). This effect was abolished in the presence of LY294002 (P < 0.001) or an IGF1R neutralizing antibody (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

This study uses an in vitro model of attachment that uses mouse blastocysts and human endometrial cells. This involves a species crossover and although this use has been well documented as a model for attachment (as human embryo numbers are limited) the results should be interpreted carefully.

WIDER IMPLICATIONS OF THE FINDINGS

This study presents mechanisms by which IGF1 improves attachment of blastocysts to Ishikawa cells and documents for the first time how IGF1 can increase adhesion competency in blastocysts. Failure of the blastocyst to implant is the major cause of human assisted reproductive technology (ART) failure. As growth factors are absent during embryo culture, their addition to embryo culture medium is a potential avenue to improve IVF success. In particular, IGF1 could prove to be a potential treatment for blastocysts before transfer to the uterus in an ART setting.

Viral expression of insulin-like growth factor I E-peptides increases skeletal muscle mass but at the expense of strength

Insulin-like growth factor I (IGF-I) is a protein that regulates and promotes growth in skeletal muscle. The IGF-I precursor polypeptide contains a COOH-terminal extension called the E-peptide. Alternative splicing in the rodent produces two isoforms, IA and IB, where the mature IGF-I in both isoforms is identical yet the E-peptides, EA and EB, share less than 50% homology. Recent in vitro studies show that the E-peptides can enhance IGF-I signaling, leading to increased myoblast cell proliferation and migration. To determine the significance of these actions in vivo and to evaluate if they are physiologically beneficial, EA and EB were expressed in murine skeletal muscle via viral vectors. The viral constructs ensured production of E-peptides without the influence of additional IGF-I through an inactivating mutation in mature IGF-I. E-peptide expression altered ERK1/2 and Akt phosphorylation and increased satellite cell proliferation. EB expression resulted in significant muscle hypertrophy that was IGF-I receptor dependent. However, the increased mass was associated with a loss of muscle strength. EA and EB have similar effects in skeletal muscle signaling and on satellite cells, but EB is more potent at increasing muscle mass. Although sustained EB expression may drive hypertrophy, there are significant physiological consequences for muscle.

Anabolic effects of IGF-1 signaling on the skeleton

This review focuses on the anabolic effects of IGF-1 signaling on the skeleton, emphasizing the requirement for IGF-1 signaling in normal bone formation and remodeling. We first discuss the genomic context, splicing variants, and species conservation of the IGF-1 locus. The modulation of IGF-1 action by growth hormone (GH) is then reviewed while also discussing the current model which takes into account the GH-independent actions of IGF-1. Next, the skeletal phenotypes of IGF-1-deficient animals are described in both embryonic and postnatal stages of development, which include severe dwarfism and an undermineralized skeleton. We then highlight two mechanisms by which IGF-1 exerts its anabolic action on the skeleton. Firstly, the role of IGF-1 signaling in the modulation of anabolic effects of parathyroid hormone (PTH) on bone will be discussed, presenting in vitro and in vivo studies that establish this concept and the proposed underlying molecular mechanisms involving Indian hedgehog (Ihh) and the ephrins. Secondly, the crosstalk of IGF-1 signaling with mechanosensing pathways will be discussed, beginning with the observation that animals subjected to skeletal unloading by hindlimb elevation are unable to mitigate cessation of bone growth despite infusion with IGF-1 and the failure of IGF-1 to activate its receptor in bone marrow stromal cell cultures from unloaded bone. Disrupted crosstalk between IGF-1 signaling and the integrin mechanotransduction pathways is discussed as one of the potential mechanisms for this IGF-1 resistance. Next, emerging paradigms on bone-muscle crosstalk are examined, focusing on the potential role of IGF-1 signaling in modulating such interactions. Finally, we present a future outlook on IGF research.

E-peptides control bioavailability of IGF-1

Insulin-like growth factor 1 (IGF-1) is a potent cytoprotective growth factor that has attracted considerable attention as a promising therapeutic agent. Transgenic over-expression of IGF-1 propeptides facilitates protection and repair in a broad range of tissues, although transgenic mice over-expressing IGF-1 propeptides display little or no increase in IGF-1 serum levels, even with high levels of transgene expression. IGF-1 propeptides are encoded by multiple alternatively spliced transcripts including C-terminal extension (E) peptides, which are highly positively charged. In the present study, we use decellularized mouse tissue to show that the E-peptides facilitate in vitro binding of murine IGF-1 to the extracellular matrix (ECM) with varying affinities. This property is independent of IGF-1, since proteins consisting of the E-peptides fused to relaxin, a related member of the insulin superfamily, bound equally avidly to decellularized ECM. Thus, the E-peptides control IGF-1 bioavailability by preventing systemic circulation, offering a potentially powerful way to tether IGF-1 and other therapeutic proteins to the site of synthesis and/or administration.

The insulin-like growth factor (IGF) signaling axis and hepatitis C virus-associated carcinogenesis (review)

Insulin-like growth factor (IGF) signaling plays an important autocrine, paracrine and endocrine role in growth promotion involving various tissues and organs. Synthesis of both IGFs (IGF-1 and IGF-2) in normal conditions takes place mainly in the liver even if the proteins can be produced in every cell of the human body. The alterations in the IGF signaling axis in human hepatocarcinogenesis are described, but mechanisms of the interactions between expression of oncogenic hepatitis C virus (HCV) proteins and components of the IGF system in progression of chronic hepatitis C to primary hepatocellular carcinoma (HCC) have been poorly recognised. In advanced stages of liver diseases, lowered serum levels of IGF-1 and IGF-2 have been documented. This was supposed to reflect significant damage to liver parenchyma, a decreased number of growth hormone receptors and a decreased genomic expression of IGF binding proteins (IGF BPs). In HCC, a decreased tissue expression of IGF-1, and an increased expression of IGF-1 receptor (IGF-1R) were noted, compared to the control. Potential mechanisms of augmented IGF-2 expression in HCC were also described and dysregulation of IGF signaling in HCC was concluded to occur predominantly at the level of IGF-2 bioavailability. The review aimed at presentation of involvement of IGF-1, IGF-1R and IGF BPs (mostly IGF BP-3 and IGF BP-6) in HCV-related hepatocarcinogenesis. Manifestation of various mRNA transcripts and IGF-1 proteins and their potential involvement in carcinogenesis are also discussed.

Role of insulin-like growth factors (IGFs), their receptors and genetic regulation in the chondrogenesis and growth of the mandibular condylar cartilage

Growth of the mandibular condylar cartilage (MCC) is reviewed as a function of genetic and epigenetic factors. The growth centers around the differential spatial concentration of the chondrocytes, influence of growth factors like TGF-β and heterogeneity in the number of IGF receptors, control the action of IGF. Besides these factors, growth of the mandibular condyle is influenced by differential response of chondrocytes as a function of their source/ageing, which in turn is regulated by TGF-β, BMPs and IGFs. While IGF-1 promotes proteoglycan synthesis and survival of the chondrocytes to maintain cartilage homeostasis, TGF-β synergistically catalysed the effect of IGF-1, while BMPs catalysed proteolysis as and when physiologically needed. To understand these processes, role of IGF-1 and its six receptors is at the center to a number of physiological processes being regulated by its mode of application for the growth and differentiation. Probing deeper, biological functions of IGFs seemed to depend on their level of free status rather than bound status to respective IGF-binding proteins (IGF-BPs), considered prerequisite to modulate their biological functions. Genetic regulation of their secretion has thrown light on their insulin-like structural homology, level and response in osteo-arthritis (OA), rheumatic arthritis (RA) and diabetes type-II. Biochemistry and spatial distribution of IGF receptors in different domains exerts control on IGF-1 activities. In ultimate analysis, IGF-axis conserved during the evolution to regulate cell growth and proliferation affect nearly every organ in the body as judged from the techniques determining skeletal maturity and decision making dependent on it for orthodontic, orthognathic/orthopedic and dental implant applications.

Mex3c regulates insulin-like growth factor 1 (IGF1) expression and promotes postnatal growth

Mex3c is highly expressed in the testis, brain, and developing bone. Mex3c mutation causes postnatal growth retardation and background-dependent perinatal lethality, possibly through impairing the translation of insulin-like growth factor 1 mRNA in bone-forming cells.

Insulin-like growth factor 1 (IGF1) mediates the growth-promoting activities of growth hormone. How Igf1 expression is regulated posttranscriptionally is unclear. Caenorhabditis elegans muscle excess 3 (MEX-3) is involved in cell fate specification during early embryonic development through regulating mRNAs involved in specifying cell fate. The function of its mammalian homologue, MEX3C, is unknown. Here we show that MEX3C deficiency in Mex3c homozygous mutant mice causes postnatal growth retardation and background-dependent perinatal lethality. Hypertrophy of chondrocytes in growth plates is significantly impaired. Circulating and bone local production of IGF1 are both decreased in mutant mice. Mex3c mRNA is strongly expressed in the testis and the brain, and highly expressed in resting and proliferating chondrocytes of the growth plates. MEX3C is able to enrich multiple mRNA species from tissue lysates, including Igf1. Igf1 expression in bone is decreased at the protein level but not at the mRNA level, indicating translational/posttranslational regulation. We propose that MEX3C protein plays an important role in enhancing the translation of Igf1 mRNA, which explains the perinatal lethality and growth retardation observed in MEX3C-deficient mice.

Expression of insulin-like growth factor 1 isoforms in the rabbit oculomotor system

OBJECTIVE

The insulin-like growth factor-1 (IGF-1) gene encodes two isoforms, IGF-1Ea and IGF-1Eb. Both isoforms can regulate skeletal muscle growth and strength. It has been suggested that IGF-Eb may be more potent in promoting skeletal muscle hypertrophy. Precise contractile force regulation is particularly important in the oculomotor system. However, expression of these isoforms in mammalian extraocular muscles (EOMs) is unknown. Here, we examined their expression in rabbit EOMs and the innervating nerve, two potential sources for myogenic growth factors, and compared isoform expression between EOMs and limb skeletal muscles.

DESIGN

Expression of IGF-1 isoforms was quantified by real-time RT-PCR in adult rabbit EOMs, trochlear and ophthalmic nerves, and compared with expression in rabbit limb skeletal muscles. The presence of mature IGF-1 peptide in the muscles was further examined by Western blot.

RESULTS

Both IGF-1Ea and IGF-1Eb were expressed in the EOM and the trochlear nerve. Both isoforms were expressed at significantly higher levels (9-fold) in EOM than in limb skeletal muscle. Transcripts of IGF-1 isoforms, of IGF-1 receptor and of IGF binding proteins showed a gradient distribution along the EOM from proximal to distal. The mature IGF-1 protein showed the same gradient distribution in the EOM.

CONCLUSIONS

Expression of relatively abundant amounts of both IGF-1 splicing isoforms in EOMs, and at a significantly higher level than in limb skeletal muscle, underscores the potential relevance of these myogenic growth factors in EOM plasticity and force regulation.

Loss of IGF-IEa or IGF-IEb impairs myogenic differentiation

Actions of protein products resulting from alternative splicing of the Igf1 gene have received increasing attention in recent years. However, the significance and functional relevance of these observations remain poorly defined. To address functions of IGF-I splice variants, we examined the impact of loss of IGF-IEa and IGF-IEb on the proliferation and differentiation of cultured mouse myoblasts. RNA interference-mediated reductions in total IGF-I, IGF-IEa alone, or IGF-IEb alone had no effect on cell viability in growth medium. However, cells deficient in total IGF-I or IGF-IEa alone proliferated significantly slower than control cells or cells deficient in IGF-IEb in serum-free media. Simultaneous loss of both or specific loss of either splice variant significantly inhibited myosin heavy chain (MyHC) immunoreactivity by 70-80% (P < 0.01) under differentiation conditions (48 h in 2% horse serum) as determined by Western immunoblotting. This loss in protein was associated with reduced MyHC isoform mRNAs, because reductions in total IGF-I or IGF-IEa mRNA significantly reduced MyHC mRNAs by approximately 50-75% (P < 0.05). Loss of IGF-IEb also reduced MyHC isoform mRNA significantly, with the exception of Myh7, but to a lesser degree (∼20-40%, P < 0.05). Provision of mature IGF-I, but not synthetic E peptides, restored Myh3 expression to control levels in cells deficient in IGF-IEa or IGF-IEb. Collectively, these data suggest that IGF-I splice variants may regulate myoblast differentiation through the actions of mature IGF-I and not the E peptides.

Nocturnin suppresses igf1 expression in bone by targeting the 3' untranslated region of igf1 mRNA

IGF-I is an anabolic factor that mediates GH and PTH actions in bone. Expression of skeletal Igf1 differs for inbred strains of mice, and Igf expression levels correlate directly with bone mass. Previously we reported that peroxisome proliferator-activated receptor-γ2 activation in bone marrow suppressed Igf1 expression and that peroxisome proliferator-activated receptor-γ2 activation-induced Nocturnin (Noc) expression, a circadian gene with peak expression at light offset, which functions as a deadenylase. In 24-h studies we found that Igf1 mRNA exhibited a circadian rhythm in femur with the lowest Igf1 transcript levels at night when Noc transcripts were highest. Immunoprecipitation/RT-PCR analysis revealed a physical interaction between Noc protein and Igf1 transcripts. To clarify which portions of the Igf1 3' untranslated region (UTR) were necessary for regulation by Noc, we generated luciferase constructs containing various lengths of the Igf1 3'UTR. Noc did not affect the 170-bp short-form 3'UTR, but suppressed luciferase activity in constructs bearing the longer-form 3'UTR, which contains a number of potential regulatory motifs involved in mRNA degradation. C57BL/6J mice have low skeletal Igf1 mRNA compared with C3H/HeJ mice, and the Igf1 3' UTR is polymorphic between these strains. Interestingly, the activity of luciferase constructs bearing the long-form 3'UTR from C57BL/6J mice were repressed by Noc overexpression, whereas those bearing the corresponding region from C3H/HeJ were not. In summary, Noc interacts with Igf1 in a strain- and tissue-specific manner and reduces Igf1 expression by targeting the longer form of the Igf1 3'UTR. Posttranscriptional regulation of Igf1 may be critically important during skeletal acquisition and maintenance.

Class 2 IGF-1 isoforms are dispensable for viability, growth and maintenance of IGF-1 serum levels

Insulin-like growth factor 1 (IGF-1) is a pleiotropic factor involved in growth, cell survival and cellular differentiation. It exerts its functions through endocrine, paracrine or autocrine mechanisms. Circulating IGF-1 is essential for normal fetal and postnatal growth, although the published phenotypes of IGF-1 null animals have been only partially penetrant, presumably due to mixed genetic backgrounds. Molecular dissection of IGF-1 action is complicated by the existence of at least nine different IGF-1 isoforms, generated in both humans and rodents by usage of alternate promoters, differential splicing and different post-translational modifications. Several lines of evidence suggest that the Class 2 IGF-1 isoform is specifically destined for circulation, supporting an endocrine role of IGF-1 in normal growth processes. Using Cre/LoxP conditional gene targeting of exon 2 of the IGF-1 gene, we have generated a Class 2 IGF-1 knockout mouse line in a pure C57/Bl6 genetic background, where the specific removal of exon 2 ablated Class 2 IGF-1 isoform. Class 2 IGF-1 knockout mice exhibited normal development and postnatal growth patterns and had normal IGF-1 circulating levels, due to compensatory upregulation of Class 1 transcripts. In contrast, progeny of a total IGF-1 knockout line lacking exon 3 in the same genetic background were predictably smaller, displayed dramatically reduced IGF-1 receptor phosphorylation and all died perinatally, apparently due to respiratory failure. These results confirm that Class 2 signal peptide is not necessary for systemic circulation of IGF-1, revealing an internal compensation system for maintaining IGF-1 serum concentrations. We also uncover a vital requirement of IGF-1 for perinatal viability, previously obscured by modifiers in heterogeneous genetic backgrounds.

Minireview: Mechano-growth factor: a putative product of IGF-I gene expression involved in tissue repair and regeneration

The discovery that IGF-I mRNAs encoding isoforms of the pro-IGF-I molecule are differentially regulated in response to mechanical stress in skeletal muscle has been the impetus for a number of studies designed to demonstrate that alternative splicing of IGF-I pre-mRNA involving exons 4, 5, and 6 gives rise to a unique peptide derived from pro-IGF-I that plays a novel role in myoblast proliferation. Research suggests that after injury to skeletal muscle, the IGF-IEb mRNA splice variant is up-regulated initially, followed by up-regulation of the IGF-IEa splice variant at later time points. Up-regulation of IGF-IEb mRNA correlates with markers of satellite cell and myoblast proliferation, whereas up-regulation of IGF-IEa mRNA is correlated with differentiation to mature myofibers. Due to the apparent role of IGF-IEb up-regulation in muscle remodeling, IGF-IEb mRNA was also named mechano-growth factor (MGF). A synthetically manufactured peptide (also termed MGF) corresponding to the 24 most C-terminal residues of IGF-IEb has been shown to promote cellular proliferation and survival. However, no analogous peptide product of the Igf1 gene has been identified in or isolated from cultured cells, their conditioned medium, or in vivo animal tissues or biological fluids. This review will discuss the relationship of the Igf1 gene to MGF and will differentiate actions of synthetic MGF from any known product of Igf1. Additionally, the role of MGF in satellite cell activation, aging, neuroprotection, and signaling will be discussed. A survey of outstanding questions relating to MGF will also be provided.

Epigenetics: intrauterine growth retardation (IUGR) modifies the histone code along the rat hepatic IGF-1 gene

Intrauterine growth restriction (IUGR) decreases serum insulin growth factor-1 (IGF-1) levels. IGF-1 is an epigenetically regulated gene that has two promoters, alternative exon 5 splicing, and multiple termination sites. The regulation of gene expression involves the whole gene, as evidenced by the aforementioned IGF-1 paradigm. We hypothesized that IUGR in the rat would affect hepatic IGF-1 expression and alter the epigenetic characteristics of the IGF-1 gene along its length. IUGR was induced through a bilateral uterine artery ligation of the pregnant rat, a well-characterized model of IUGR. Pups from anesthesia and sham-operated dams were used as controls. Real-time RT-PCR and ELISA was used to measure expression at day of life (DOL) 0 and 21. Bisulfite sequencing and chromatin immunoprecipitation (ChIP) quantified IGF-1 epigenetic characteristics. A nontranscribed intergenic control was used for ChIP studies. IUGR decreased hepatic and serum IGF-1. Concurrently, IUGR modified epigenetic characteristics, particularly the histone code, along the length of the hepatic IGF-1 gene. Many changes persisted postnatally, and the postnatal effect of IUGR on the histone code was gender-specific. We conclude that IUGR modifies epigenetic characteristics of the rat hepatic IGF-1 gene along the length of the whole gene.

Transcriptional regulation and biological significance of the insulin like growth factor II gene

The insulin like growth factors I and II are the most ubiquitous in the mammalian embryo. Moreover they play a pivotal role in the development and growth of tumours. The bioavailability of these growth factors is regulated on a transcriptional as well as on a posttranslational level. The expression of non-signalling receptors as well as binding proteins does further tune the local concentration of IGFs. This paper aims at reviewing how the transcription of the IGF genes is regulated. The biological significance of these control mechanisms will be discussed.

Ki-energy (life-energy) stimulates osteoblastic cells and inhibits the formation of osteoclast-like cells in bone cell culture models

Some practitioners of the Nishino Breathing Method (NBM) were found to have a higher bone density than the average values of age- and gender-matched non-practitioners. Using bone cell culture models, we investigated a possible mechanism behind this observation. For the study of bone mineralization, we performed the following two experiments using cultured osteoblastic MC3T3-E1 cells: (i) Kozo Nishino, a Japanese Ki expert, sent Ki-energy to the cells once for 5 or 10 min after they were seeded in culture dishes in the presence of 10% fetal bovine serum (FBS). They were incubated for 72 h and the cells were counted. The number in the dish with 10-min Ki-exposure was significantly greater than that in the control (P < 0.01 with n = 8). We performed a reverse transcription-polymerase chain reaction (RT-PCR) study using these cells, but the mRNA expressions did not change significantly. (ii) After cells were incubated for 72 h without Ki-exposure (in the presence of FBS), they were further cultured for 48 h (in the absence of FBS) to promote differentiation. At the beginning of the second culture stage, Ki was applied once for 10 min. After 48 h, RT-PCR was performed. The mRNA expressions which are related to bone mineralization, such as Runx2, alpha1(I) collagen, alkaline phosphatase and osteocalcin, increased significantly (P < 0.05 and n = 4 for all). For the bone resorption study, we used mouse marrow cultures, which can form osteoclast-like cells in the presence of (1-34) parathyroid hormone (PTH), and stimulate resorption. We exposed these cells to Ki-energy twice for the duration of 5 or 10 min on day 0 and day 4. On day 7, the cells were counted. The number of osteoclast-like cells in dishes with Ki exposure was significantly smaller than those in control dishes (P < 0.05 with n = 5). The difference between 5-min exposure and 10-min exposure was not statistically significant. All of our data suggest that the Ki-effect on osteoporosis should be further explored.

Neuroendocrinology of protochordates: Insights from Ciona genomics

The genome for two species of Ciona is available making these tunicates excellent models for studies on the evolution of the chordates. In this review most of the data is from Ciona intestinalis, as the annotation of the C. savignyi genome is not yet available. The phylogenetic position of tunicates at the origin of the chordates and the nature of the genome before expansion in vertebrates allows tunicates to be used as a touchstone for understanding genes that either preceded or arose in vertebrates. A comparison of Ciona, a sea squirt, to other model organisms such as a nematode, fruit fly, zebrafish, frog, chicken and mouse shows that Ciona has many useful traits including accessibility for embryological, lineage tracing, forward genetics, and loss- or gain-of-function experiments. For neuroendocrine studies, these traits are important for determining gene function, whereas the availability of the genome is critical for identification of ligands, receptors, transcription factors and signaling pathways. Four major neurohormones and their receptors have been identified by cloning and to some extent by function in Ciona: gonadotropin-releasing hormone, insulin, insulin-like growth factor, and cionin, a member of the CCK/gastrin family. The simplicity of tunicates should be an advantage in searching for novel functions for these hormones. Other neuroendocrine components that have been annotated in the genome are a multitude of receptors, which are available for cloning, expression and functional studies.

Rskalpha-actin/hIGF-1 transgenic mice with increased IGF-I in skeletal muscle and blood: impact on regeneration, denervation and muscular dystrophy

Human IGF-I was over-expressed in skeletal muscles of C57/BL6xCBA mice under the control of the rat skeletal alpha-actin gene promoter. RT-PCR verified expression of the transgene in skeletal muscle but not in the liver of 1- and 21-day old heterozygote transgenic mice. The concentration of endogenous mouse IGF-I, measured by an immunoassay which does not detect human IGF-I, was not significantly different between transgenic mice and wild-type littermates (9.5 +/- 0.8 and 13.3 +/- 1.9 ng/g in muscle; 158.3 +/- 18.6 and 132.9 +/- 33.1 ng/ml in plasma, respectively). In contrast, quantitation with antibodies to human IGF-I showed an increase in IGF-I of about 100 ng/ml in plasma and 150 ng/g in muscle of transgenic mice at 6 months of age. Transgenic males, compared to their age matched wild-type littermates, had a significantly higher body weight (38.6 +/- 0.53 g vs. 35.8 +/- 0.64 g at 6 months of age; P < 0.001), dry fat-free carcass mass (5.51 +/- 0.085 vs. 5.08 +/- 0.092 g; P < 0.001) and myofibrillar protein mass (1.62 +/- 0.045 vs. 1.49 +/- 0.048 g; P < 0.05), although the fractional content of fat in the carcass was lower (167 +/- 7.0 vs. 197 +/- 7.7 g/kg wet weight) in transgenic animals. There was no evidence of muscle hypertrophy and no change in the proportion of slow type I myofibres in the limb muscles of Rskalpha-actin/hIGF-I transgenic mice at 3 or 6 months of age. Phenotypic changes in Rskalpha-actin/hIGF-I mice are likely to be due to systemic as well as autocrine/paracrine effects of overproduction of IGF-I due to expression of the human IGF-I transgene. The effect of muscle specific over-expression of Rskalpha-actin/hIGF-I transgene was tested on: (i) muscle regeneration in auto-transplanted whole muscle grafts; (ii) myofibre atrophy following sciatic nerve transection; and (iii) sarolemmal damage and myofibre necrosis in dystrophic mdx muscle. No beneficial effect of muscle specific over-expression of Rskalpha-actin/hIGF-I transgene was seen in these three experimental models.

Organ-specific and age-dependent expression of insulin-like growth factor-I (IGF-I) mRNA variants: IGF-IA and IB mRNAs in the mouse

Insulin-like growth factor-I (IGF-I) gene generates several IGF-I mRNA variants by alternative splicing. Two promoters are present in mouse IGF-I gene. Each promoter encodes two IGF-I mRNA variants (IGF-IA and IGF-IB mRNAs). Variants differ by the presence (IGF-IB) or absence (IGF-IA) of a 52-bp insert in the E domain-coding region. Functional differences among IGF-I mRNAs, and regulatory mechanisms for alternative splicing of IGF-I mRNA are not yet known. We analyzed the expression of mouse IGF-IA and IGF-IB mRNAs using SYBR Green real-time RT-PCR. In the liver, IGF-I mRNA expression increased from 10 days of age to 45 days. In the uterus and ovary, IGF-I mRNA expression increased from 21 days of age, and then decreased at 45 days. In the kidney, IGF-I mRNA expression decreased from 10 days of age. IGF-IA mRNA levels were higher than IGF-IB mRNA levels in all organs examined. Estradiol-17beta (E2) treatment in ovariectomized mice increased uterine IGF-IA and IGF-IB mRNA levels from 3 hr after injection, and highest levels for both mRNAs were detected at 6 hr, and relative increase was greater for IGF-IB mRNA than for IGF-IA mRNA. These results suggest that expression of IGF-I mRNA variants is regulated in organ-specific and age-dependent manners, and estrogen is involved in the change of IGF-I mRNA variant expression.

IGF-I increases bone marrow contribution to adult skeletal muscle and enhances the fusion of myelomonocytic precursors

Muscle damage has been shown to enhance the contribution of bone marrow-derived cells (BMDCs) to regenerating skeletal muscle. One responsible cell type involved in this process is a hematopoietic stem cell derivative, the myelomonocytic precursor (MMC). However, the molecular components responsible for this injury-related response remain largely unknown. In this paper, we show that delivery of insulin-like growth factor I (IGF-I) to adult skeletal muscle by three different methods-plasmid electroporation, injection of genetically engineered myoblasts, and recombinant protein injection-increases the integration of BMDCs up to fourfold. To investigate the underlying mechanism, we developed an in vitro fusion assay in which co-cultures of MMCs and myotubes were exposed to IGF-I. The number of fusion events was substantially augmented by IGF-I, independent of its effect on cell survival. These results provide novel evidence that a single factor, IGF-I, is sufficient to enhance the fusion of bone marrow derivatives with adult skeletal muscle.

Phenotypic improvement of dystrophic muscles by rAAV/microdystrophin vectors is augmented by Igf1 codelivery

The absence of dystrophin in Duchenne muscular dystrophy (DMD) leads to sarcolemmal instability and enhances the susceptibility of muscle fibers to contraction-induced injury. Various viral vectors have been used to deliver mini- and microdystrophin expression cassettes to muscles of dystrophin-deficient mdx mice, significantly increasing both the morphological and the functional properties of the muscles. However, dystrophin delivery to adult mdx mice has not yielded a complete rescue of the dystrophic phenotype. Here we investigated a novel strategy involving dual gene transfer of recombinant adeno-associated viral vectors expressing either microdystrophin (rAAV-muDys) or a muscle-specific isoform of Igf-1 (rAAV-mIgf-1). Injection of mdx muscles with rAAV-muDys reduced myofiber degeneration and turnover and increased their resistance to mechanical injury, but did not increase muscle mass or force generation. Injection of mdx muscles with rAAV-mIgf-1 led to increased muscle mass, but did not provide protection against mechanical injury or halt myofiber degeneration, leading to loss of the vector over time. In contrast, co-injection of the rAAV-muDys and rAAV-mIgf-1 vectors resulted in increased muscle mass and strength, reduced myofiber degeneration, and increased protection against contraction-induced injury. These results suggest that a dual-gene, combinatorial strategy could enhance the efficacy of gene therapy of DMD.

Expression profile of osteoblast lineage at defined stages of differentiation

The inherent heterogeneity of bone cells complicates the interpretation of microarray studies designed to identify genes highly associated with osteoblast differentiation. To overcome this problem, we have utilized Col1a1 promoter-green fluorescent protein transgenic mouse lines to isolate bone cells at distinct stages of osteoprogenitor maturation. Comparison of gene expression patterns from unsorted or isolated sorted bone cell populations at days 7 and 17 of calvarial cultures revealed an increased specificity regarding which genes are selectively expressed in a subset of bone cell types during differentiation. Furthermore, distinctly different patterns of gene expression associated with major signaling pathways (Igf1, Bmp, and Wnt) were observed at different levels of maturation. Some of our data differ from current models of osteoprogenitor cell differentiation and emphasize components of the pathways that were not revealed in studies based on a total cell population. Thus, applying methods to generate more homogeneous populations of cells at a defined level of cellular differentiation from a primary osteogenic culture is feasible and leads to a novel interpretation of the gene expression associated with increasing levels of osteoprogenitor maturation.

Allelic differences in a quantitative trait locus affecting insulin-like growth factor-I impact skeletal acquisition and body composition

Insulin-like growth factor-I (IGF-I) is critical for optimal skeletal growth and maintenance. Knockout and transgenic models have provided significant insights into the role of IGF-I in bone modeling and remodeling. Congenic mice demonstrate allelic differences in particular quantitative trait loci (QTL). One such model is congenic 6T, which contains a QTL for reduced serum IGF-I donated from C3H/HeJ on a pure C57Bl/6 J (B6) background. In this study we found a 30%-50% reduction in IGF-I expression in bone, liver, and fat of the congenic 6T mouse, as well as lower circulating IGF-I compared with control B6. 6T mice also had a greater percentage body fat, but reduced serum leptin. These changes were associated with reduced cortical and trabecular bone mineral density, impaired bone formation but no change in bone resorption. Moreover, the anabolic skeletal response to intermittent parathyroid hormone (PTH) therapy was blunted in 6T compared with B6, potentially in response to greater programmed cell death in osteocytes and osteoblasts of 6T. In summary, allelic differences in IGF-I expression impact peak bone acquisition and body composition, as well as the skeletal response to PTH. Lifelong changes in circulating and skeletal IGF-I may be relevant for the pathophysiology of several diseases, including chronic renal failure.

Reconciling data from transgenic mice that overexpress IGF-I specifically in skeletal muscle

Transgenic mice that overexpress insulin-like growth factor-1 (IGF-I) specifically in skeletal muscle have generated much information about the role of this factor for muscle growth and remodelling and provide insight for therapeutic applications of IGF-I for different pathological states and ageing. However, difficulties arise when attempting to critically compare the significance of data obtained in vivo by using different genetically engineered mouse lines and various experimental models. Complications arise due to complexity of the IGF-I system, since multiple transcripts of the IGF-I gene encode different isoforms generated by alternate promoter usage, differential splicing and post-translational modification, and how IGF-I gene expression relates to its diverse autocrine, paracrine and endocrine modes of action in vivo has still to be elucidated. In addition, there are problems related to specification of the exact IGF-I isoform used, expression patterns of the promoters, and availability of the transgene product under different experimental conditions. This review discusses the factors that must be considered when reconciling data from cumulative studies on IGF-I in striated muscle growth and differentiation using genetically modified mice. Critical evaluation of the literature focuses specifically on: (1) the importance of detailed information about the IGF-I isoforms and their mode of action (local, systemic or both); (2) expression pattern and strength of the promoters used to drive transgenic IGF-I in skeletal muscle cells (mono and multi-nucleated); (3) local compared with systemic action of the transgene product and possible indirect effects of transgenic IGF-I due to upregulation of other genes within skeletal muscle; (4) re-interpretation of these results in light of the most recent approaches to the dissection of IGF-I function. Full understanding of these complex in vivo issues is essential, not only for skeletal muscle but for many other tissues, in order to effectively extend observations derived from transgenic studies into potential clinical situations.

Suppressive effect of regucalcin on cell differentiation and mineralization in osteoblastic MC3T3-E1 cells

The role of regucalcin in the regulation of osteoblastic cell function was investigated. Osteoblastic MC3T3-E1 cells with subconfluent monolayers were cultured in a medium containing regucalcin (10(-10)-10(-8) M) without fetal bovine serum (FBS). The proliferation of osteoblastic cells was not significantly altered in the presence of regucalcin. The results of reverse transcription-polymerase chain reaction (RT-PCR) analysis with specific primers showed that the expression of Runx2 (Cbfa1) and insulin-like growth factor-I (IGF-I) mRNAs in osteoblastic cells was significantly suppressed in the presence of regucalcin (10(-10) or 10(-9) M). Transforming growth factor-beta1 mRNA levels were significantly enhanced in the 24 h-culture with regucalcin (10(-10) or 10(-9) M). Alpha1(I) collagen and glyceroaldehyde-3-phosphate dehydrogenase (G3PDH) mRNA levels were not significantly changed by culture with regucalcin (10(-10) or 10(-9) M). Alkaline phosphatase activity was significantly decreased in the lysate of cells cultured for 24 or 48 h with regucalcin (10(-10)-10(-8) M). Moreover, the expression of regucalcin in osteoblastic cells was demonstrated by RT-PCR and Western blot analysis. When regucalcin (10(-7) M) was added into the enzyme reaction mixture containing the lysate of osteoblastic cells cultured in the absence of regucalcin, alkaline phosphatase activity was significantly decreased. Also, Ca2+/calmodulin-dependent nitric oxide (NO) synthase activity in the cell lysate was significantly decreased by addition of regucalcin (10(-10)-10(-8) M) into the reaction mixture. The presence of anti-regucalcin monoclonal antibody (5 or 10 ng/ml) in the enzyme reaction mixture caused a significant increase in NO synthase activity in the cell lysate in the presence or absence of Ca2+/calmodulin, suggesting a role of endogenous regucalcin. When osteoblastic cells with subconfluency were cultured in the presence of regucalcin (10(-10) or 10(-9) M) for 3, 9, or 18 days, the results with Alizarin red staining showed that the mineralization was markedly suppressed by culture with regucalcin for 3, 9, or 18 days. This study demonstrates that regucalcin regulates the function of osteoblastic cells, and that the protein suppresses cell differentiation and mineralization.

MRI and in situ hybridization reveal early disturbances in brain size and gene expression in the megencephalic (mceph/mceph) mouse

The mouse model for megencephaly, mceph/mceph, carries a truncating deletion in the Shaker-related voltage gated potassium channel gene 1. Affected mice display neurological disturbances and motor dysfunctions. Symptoms begin to show at 3-4 weeks of age. The cause of the brain enlargement is not clear. To elucidate early events in the development of the disease we used magnetic resonance imaging (MRI) to quantify, over time, the increase in size of several discrete brain regions in the same mice at 3, 8 and 12 weeks of age. We also analysed markers for neuropeptides and growth factors to explore their possible involvement at an early stage. The results show an enlargement of the total coronal area of the brain already at 3 weeks of age. Total brain volume, ventral cortex, hippocampal formation and cerebral cortex were enlarged at 8 weeks and onwards. Thalamus, brainstem, cerebellum and spinal cord did not differ from controls even at 12 weeks. We also report distinct disturbances in the expression of brain-derived neurotrophic factor, insulin-like growth factor binding protein 6 and several neuropeptides at 2 and 3 weeks of age, that is, before an obvious behavioural phenotype can be observed. These results provide an objective description of the size changes in different brain regions of the mceph/mceph mouse, and suggest that certain molecules could be involved in the early processes underlying these changes.

Expression of parathyroid hormone-related peptide and insulin-like growth factor I during rat fracture healing

Parathyroid hormone-related peptide (PTHrP) and insulin-like growth factor I (IGF-I) are both involved in the regulation of bone and cartilage metabolisms and their interaction has been reported in osteoblasts. To investigate the interaction of PTHrP and IGF-I during fracture healing, the expression of mRNA for PTHrP and IGF-I, and receptors for PTH/PTHrP and IGF were examined during rat femoral fracture healing using an in situ hybridization method and an immunohistochemistry method, respectively. During intramembranous ossification, PTHrP mRNA, IGF-I mRNA and IGF receptors were detected in preosteoblasts, differentiated osteoblasts and osteocytes in the newly formed trabecular bone. PTH/PTHrP receptors were markedly detected in osteoblasts and osteocytes, but only barely so in preosteoblasts. During cartilaginous callus formation, PTHrP mRNA was expressed by mesenchymal cells and proliferating chondrocytes. PTH/PTHrP receptors were detected in proliferating chondrocytes and early hypertrophic chondrocytes. IGF-I mRNA and IGF receptor were co-expressed by mesenchymal cells, proliferating chondrocytes, and early hypertrophic chondrocytes. At the endochondral ossification front, osteoblasts were positive for PTHrP and IGF-I mRNA as well as their receptors. These results suggest that IGF-I is involved in cell proliferation or differentiation in mesenchymal cells, periosteal cells, osteoblasts and chondrocytes in an autocrine and/or paracrine fashion. Furthermore, PTHrP may be involved in primary callus formation presumably co-operating with IGF-I in osteoblasts and osteocytes, and by regulating chondrocyte differentiation in endochondral ossification.

Developmental failure of hybrid embryos generated by in vitro fertilization of water buffalo (Bubalus bubalis) oocyte with bovine spermatozoa

The developmental potential of inter-species hybrid embryos produced by in vitro fertilization of in vitro matured buffalo oocytes with bovine spermatozoa was studied with a view to investigate pre-implantation embryo development and its gross morphology, early embryonic gene expression, and embryonic genome activation. Fertilization events with both buffalo and cattle spermatozoa were almost similar. Overall fertilization rate with cattle spermatozoa was 78.4% was not significantly different from that of buffalo spermatozoa (80.2%). Initial cleavage rate between buffalo and hybrid embryo was also similar, and there was no significant difference in their developmental rate till 8-cell stage (26.0 +/- 4.1 vs. 24.3 +/- 4.8). However, only 5.3% of hybrid embryos developed into blastocyst stage compared to 21.7% in buffalo. mRNA phenotyping of insulin-like growth factor family (Insulin, insulin receptor, IGF-I, IGF-I receptor, IGF-II, and IGF-II receptor) and glucose transporter isoforms (GLUT-I, II, III, IV) in hybrid embryos clearly showed that these molecules were not expressed after 8-cell stage onward. Similarly, as observed in buffalo embryos, incorporation of (35)S-methionine and (3)H-uridine could not be observed in hybrid embryos from 8-cell stage onward. This suggests that the maternal-zygotic genome activation did not occur in hybrid embryos. Differential staining also showed that the blastomere stopped dividing after 8-cell stage. Collectively, these parameters clearly showed that there was developmental failure of hybrid embryos.

Growth factor upregulation during obliterative bronchiolitis in the mouse model

Obliterative bronchiolitis (OB), or chronic allograft rejection, is a major cause of morbidity and mortality after lung transplantation. The goal of these experiments was to determine whether several important growth factors were upregulated during OB in the mouse heterotopic trachea model. Isografts (BALB/c into BALB/c) and allografts (BALB/c into C57BL/6) were implanted in three sets of cyclosporine-treated animals and were harvested from 2 to 10 weeks. Ribonucleic acid was isolated using the cesium chloride-guanidine method and was reverse transcribed and semiquantitated with the polymerase chain reaction using specific primers for platelet-derived growth factor (PDGF)-A and PDGF-B chains, fibroblast growth factor (FGF) isoforms 1 and 2, transforming growth factor-beta, tumor necrosis factor-alpha (TNF-alpha), edothelin-1, (prepro) epidermal growth factor, insulin-like growth factor-1, and beta-actin as a control. Transforming growth factor-beta, TNF-alpha, endothelin-1, and insulin-like growth factor-1 expression were increased 1.5-fold to 5.0-fold (p < or = 0.04 for each) in the allografts compared with the isografts at Weeks 2 through 6. Significantly increased expression of FGF-1, FGF-2, and PDGF-B was noted in the allografts at 4 weeks (p < 0.05 for each), which reversed at 6 and 10 weeks. No differences were found with the PDGF-A chain. The isografts expressed more epidermal growth factor than allografts (p < 0.001). Treatment with a TNF-alpha-soluble receptor (human TNFR:Fc) significantly reduced epithelial injury (p = 0.01) and lumenal obstruction (p = 0.037) in this model. We conclude that increased expression of a large number of growth factors occurs during OB in this model. Growth factor blockade (in particular with regard to TNF-alpha) may be useful in ameliorating OB in this model.

IGF-I, IGF-II, and IGF-receptor-1 transcript and IGF-II protein expression in myostatin knockout mice tissues

Semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry were performed to demonstrate whether a correlation exists between insulin-like growth factors (IGFs)-positive regulators of growth-and myostatin, a negative regulator of muscle growth. IGF-I, -II, and IGF-receptor-1 (IGF-R1) mRNA and IGF-II protein expressions were determined in control and myostatin knockout mice tissues. IGF-I gene expressions were similar between control and knockout mice tissues, whereas IGF-II mRNA levels were significantly higher in myostatin knockout mice kidney and soleus muscles than those of control mice (P <.01). IGF-R1 mRNA levels from control mice heart (P <.05) and kidney (P <.01) were significantly higher than in myostatin knockout mice, whereas levels were lower in pectoralis muscle of control mice than knockout mice (P <.01). The strongly IGF-II-positive cells in soleus muscle were more common in myostatin knockout mice and were seen in a few foci in control mice. IGF-II immunoreactivity in both control and myostatin knockout mice kidneys was localized to the epithelium of renal tubules and collecting ducts. Reciprocal changes in the expression of myostatin and IGF-II and IGF-R1 may underlie normal growth of skeletal muscle and other organs in mammals, and the changes in these tissues associated with disease.

Beta cell expression of IGF-I leads to recovery from type 1 diabetes

Patients with type 1 diabetes are identified after the onset of the disease, when beta cell destruction is almost complete. beta cell regeneration from islet cell precursors might reverse this disease, but factors that can induce beta cell neogenesis and replication and prevent a new round of autoimmune destruction remain to be identified. Here we show that expression of IGF-I in beta cells of transgenic mice (in both C57BL/6-SJL and CD-1 genetic backgrounds) counteracts cytotoxicity and insulitis after treatment with multiple low doses of streptozotocin (STZ). STZ-treated nontransgenic mice developed high hyperglycemia and hypoinsulinemia, lost body weight, and died. In contrast, STZ-treated C57BL/6-SJL transgenic mice showed mild hyperglycemia for about 1 month, after which they normalized glycemia and survived. After STZ treatment, all CD-1 mice developed high hyperglycemia, hypoinsulinemia, polydipsia, and polyphagia. However, STZ-treated CD-1 transgenic mice gradually normalized all metabolic parameters and survived. beta cell mass increased in parallel as a result of neogenesis and beta cell replication. Thus, our results indicate that local expression of IGF-I in beta cells regenerates pancreatic islets and counteracts type 1 diabetes, suggesting that IGF-I gene transfer to the pancreas might be a suitable therapy for this disease.

Misexpression of IGF-I in the mouse lens expands the transitional zone and perturbs lens polarization

Insulin-like growth factor-I (IGF-I) has been implicated as a regulator of lens development. Experiments performed in the chick have indicated that IGF-I can stimulate lens fiber cell differentiation and may be involved in controlling lens polarization. To assess IGF-I activity on mammalian lens cells in vivo, we generated transgenic mice in which this factor was overexpressed from the alphaA-crystallin promoter. Interestingly, we observed no premature differentiation of lens epithelial cells. The pattern of lens polarization was perturbed, with an apparent expansion of the epithelial compartment towards the posterior lens pole. The distribution of immunoreactivity for MIP26 and p57(KIP2) and a modified pattern of proliferation suggested that this morphological change was best described as an expansion of the germinative and transitional zones. The expression of IGF-I signaling components in the normal transitional zone and expansion of the transitional zone in the transgenic lens both suggest that endogenous IGF-I may provide a spatial cue that helps to control the normal location of this domain.

Expression of cholecystokinin, enkephalin, galanin and neuropeptide Y is markedly changed in the brain of the megencephaly mouse

Megencephaly, enlarged brain, is a major sign in several human neurological diseases. The mouse model for megencephaly (mceph/mceph) has an enlarged brain, presumably due to brain cell hypertrophy, and exhibits neurological and motor disturbances with seizure-like activity, as well as disturbances in the insulin-like growth factor system. Here, we report that expression of the neuropeptides cholecystokinin, enkephalin, galanin and neuropeptide Y is dramatically changed in mceph/mceph brains compared to wild type, as revealed by in situ hybridization and immunohistochemistry. The changes were confined to discrete brain regions and occurred in a parallel fashion for peptides and their transcripts. For cholecystokinin, mceph/mceph brains had region-specific up- and down-regulations in several layers of the hippocampal formation and increased levels in, especially ventral, cortical regions. Enkephalin messenger RNA expression was up-regulated in the dentate gyrus granular layer and in ventral cortices, but down-regulated in the CA1 pyramidal layer. Enkephalin-like immunoreactivity was elevated in mossy fibers of the hippocampus and the ventral cortices. Galanin expression was increased in several layers and interneurons of the hippocampal formation, as well as in ventral cortices. Galanin-like immunoreactivity was reduced in nerve terminals in the forebrain. Neuropeptide Y expression was increased in the hippocampal formation and ventral cortices. Whether the mainly increased peptide levels contribute to the excessive growth of the brain or represent a consequence of this growth and/or of the neurological and motor disturbances remains to be elucidated.

Hypothalamic CART and serum leptin levels are reduced in the anorectic (anx/anx) mouse

Cocaine- and amphetamine-regulated transcript (CART) is expressed in the hypothalamus, and putative peptides encoded by CART potently inhibit feeding when administered centrally. CART is strongly down-regulated in the lateral hypothalamic area and the arcuate nucleus in animal models of obesity with disrupted leptin signaling. Here we have used in situ hybridization and immunohistochemistry to study CART expression in mice homozygous for the anorexia (anx) mutation which are characterized by a much reduced food intake and premature death. anx/anx mice had significantly decreased levels of CART mRNA label and peptide-immunoreactive cell bodies and fibers in the arcuate nucleus and a lower number of detectable CART-expressing cells in the dorsomedial hypothalamic nucleus/lateral hypothalamic area. Moreover, serum leptin levels were significantly lower in anx/anx mice compared to normal littermates, most likely due to the prominent depletion of body fat in these animals. The decrease in the anorexigenic agents leptin and CART, may reflect a compensatory down-regulation in response to the energy-deprived state of anx/anx mice. Alternatively, the reduced arcuate CART expression may be a consequence of a molecular defect in the arcuate nucleus of these animals.

Relationship between time of first cleavage and the expression of IGF-I growth factor, its receptor, and two housekeeping genes in bovine two-cell embryos and blastocysts produced in vitro

We have previously demonstrated that there is a clear relationship between the time interval between insemination and first cleavage in vitro and the development to the blastocyst stage of bovine embryos. In addition we have shown that this developmental ability can be linked to the stability of the mRNA for several gene transcripts measured in 2-cell bovine embryos cleaving at different times. The aim of this study was to examine the relationship between bovine embryo developmental competence, assessed in terms of time of first cleavage, and the expression of insulin-like growth factor-I (IGF-I) ligand and receptor, hypoxanthine phosphoribosyl transferase (HPRT) and glucose-6-phosphate dehydrogenase (G6PD). The expression of beta-actin was used as a reference value. No differences were observed in the mRNA expression of G6PD and HPRT genes between male and female 2-cell embryos. However, the expression of these two genes was significantly higher in female blastocysts than in male blastocysts. Moreover, when the relative amount of G6PD and HPRT mRNA detected in these groups of male and female embryos was compared, there was a significant relationship between the time of first cleavage and the relative amount of mRNA: 2-cell embryos and blastocysts derived from oocytes that cleaved at 27 and 30 hr post insemination had higher levels of mRNA for G6PD and HPRT than those that cleaved after 33 hr. IGF-I ligand and receptor was detected in all blastocysts analyzed, irrespective of stage of development or time of first cleavage. In addition, the receptor was detected in all 2-cell embryos examined. In contrast, while IGF-I ligand was found in all 2-cell embryos that cleaved at 27 and 30 hpi, it was only found in some of those cleaving between 33 and 36 hpi and in none of those cleaving after 36 hr. In conclusion, we have demonstrated differences in gene expression in the early embryo that are reflective of differences in developmental competence between early- and late-cleaving zygotes.