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Biomedical subjects

P T Loughna

Publications and source records attributed to P T Loughna.

At least 19 recordsLinked to original sources
PubMed2000

Phenotypic expression of IGF binding protein transcripts in muscle, in vitro and in vivo.

The actions of the insulin-like growth factors (IGF-I and IGF-II) which are essential components of skeletal muscle growth are mediated via their receptors and modulated by six binding proteins (IGFBPs). We studied IGFBP transcripts in C2C12 cell cultures and in adult control and denervated gastrocnemius muscle. IGFBP-2, -4, -5, and -6 were detected in C2C12 cells. IGFBP-6 mRNA levels remained unchanged, IGFBP-2 levels decreased and IGFBP-4 and -5 increased over 1, 5, and 9 days after serum reduction. In a range of adult muscles studied, IGFBP-4 mRNA levels were similar, IGFBP-5 was present at different levels in slow and fast muscles and IGFBP-6 had the lowest expression in the tibialis anterior. Denervation resulted in dramatic up-regulation of IGFBP-4 and -5 transcripts but there was no change in IGFBP-6. These results suggest that either lack of neural input and/or mechanical loading, both of which contribute to muscle atrophy, affect IGFBP expression.

Animals↗
PubMed2000

The LIM-domain protein FHL1 (SLIM 1) exhibits functional regulation in skeletal muscle.

The LIM domain protein FHL1 (SLIM 1) transcript is preferentially expressed in postnatal skeletal muscle but almost nothing is known about its function in this tissue. In this study we have examined the expression of the FHL1 transcript at the cellular level by in situ hybridisation. Muscle fibers exist as a number of discrete subpopulations or "types" which are differentiated by their contractile and metabolic properties. It was observed that the FHL1 transcript was not fiber-type specific but was however more abundant in oxidative fibers. Muscle atrophy induced by disuse caused a significant decline in the expression of the transcript but atrophy induced by short-term denervation did not. Hypertrophy of skeletal muscle induced by passive stretch was associated with an up-regulation of the FHL1 transcript. These data are consistent that FHL1 is involved in synthetic processes within the muscle fibre.

Animals↗
PubMed2000

The expression of the myogenic regulatory factors in denervated and normal muscles of different phenotypes.

The nerve is known to play a pivotal role in the diversification of muscle fibre types postnatally. Reducing neuronal activity in a slow muscle such as the soleus by denervation, switches on genes associated with a fast muscle phenotype. On the other hand, denervating a fast muscle such as the extensor digitorum longus (EDL) induces the conversion of fast fibres to a 'slower' contractile phenotype. The myogenic regulatory factors (MRFs) are proposed as the regulators of muscle phenotype as MyoD and myogenin have been shown to differentially accumulate in fast and slow muscle upon the induction of fibre type transformation. The denervation model has been used in the present study to induce changes in MRF expression in the muscles of the lower hindlimb which have distinct phenotypic characteristics. The level of MRF expression in pairs of denervated and innervated soleus, EDL, tibialis anterior (TA), plantaris and gastrocnemius muscles has been determined by Northern analysis and compared. The present study has shown that each muscle responds differently to denervation with respect to the increases in MRF expression. Fast muscles responded very quickly to denervation by increasing the level of MRF transcripts while slow muscles did not show significant increases in expression after 48 h denervation. The innervated EDL (fast) and soleus (slow) muscle differed with respect to the level of MRF-4 expressed, MRF-4 being expressed at higher levels in the slow muscle compared to the fast, suggesting that MRF-4 is important in the maintenance of a slow muscle phenotype. Moreover, MRF-4 and myogenin show the greatest fold increases in expression in the fast muscles examined. MyoD and Myf 5 show less dramatic increase in expression in response to denervation but exhibit the greatest fold increases in the fast muscles compared to slow.

Animals↗
PubMed2000

MRF-4 exhibits fiber type- and muscle-specific pattern of expression in postnatal rat muscle.

The crucial role played by the myogenic regulatory factors (MRFs) in the development of skeletal muscle has been well characterized. The continued expression of these factors in skeletal muscle of the postnatal animal has led to the suggestion that they may play a role in the regulation of muscle fiber phenotype. The few studies that have examined the expression of MRF-4 in postnatal muscle have been carried out at the whole muscle level. These studies demonstrated that this factor is expressed at a higher level than any other MRF but suggested that this was not affected by muscle phenotype. In this study, the expression of the MRF-4 transcript has been examined at the cellular level by in situ hybridization. It was observed that in the mixed fiber type muscle the gastrocnemius, MRF-4 was preferentially expressed in slow muscle fibers, but in the slow postural soleus, no fiber type specificity was observed. These observations suggest that MRF-4 may play a role in the regulation of muscle fiber phenotype in the postnatal animal.

Animals↗
PubMed1999

The novel sarcomeric protein telethonin exhibits developmental and functional regulation.

We have isolated a cDNA clone from a mouse skeletal muscle library which is preferentially expressed in striated muscle and exhibits a high homology to human telethonin, a sarcomeric protein. The mouse telethonin transcript is developmentally regulated in both cardiac and skeletal muscle in vivo and is down-regulated in response to denervation. In the C2C12 muscle cell-line the mouse telethonin transcript exhibited a pattern of accumulation similar to that observed for a contractile protein and suggests a role in myofibrillar assembly.

Amino Acid Sequence↗
PubMed1999

Passive stretch modulates denervation induced alterations in skeletal muscle myosin heavy chain mRNA levels.

The effect of denervation and denervation combined with immobilisation in either the shortened or lengthened position (passive stretch) upon myosin heavy chain (MyHC) mRNA levels was examined in three rat hind-limb muscles with differing phenotypes. Denervation alone caused a reduction in type I and type IIa MyHC transcripts in all three muscles. In contrast denervation caused a 72% increase in type IIb in the slow postural soleus muscle only which was prevented by immobilisation in the lengthened position. In the same muscle passive stretch also significantly retarded the effects of denervation upon the type I transcript (from 38% below control levels to 24% below) and type IIa transcript (from 59% to 32% below control levels). The levels of both type I and IIa transcripts, in the fast phasic plantaris muscle, were both unaffected by stretch combined with denervation when compared to denervation alone. In the mixed gastrocnemius muscle stretch affected the level of the type I but not the type IIa transcript. These data suggest that passive stretch can modulate MyHC gene expression independently of innervation but that it does so in a muscle-specific manner.

Animals↗
PubMed1996

Two myogenic regulatory factor transcripts exhibit muscle-specific responses to disuse and passive stretch in adult rats.

Levels of myogenic regulatory factor (MRF) transcripts are altered in a muscle-specific manner in response to hind limb immobilisation of adult male rats, for a 2 day period, in either a lengthened or shortened position which result in passive stretch or disuse atrophy respectively. Myogenin transcript levels were dramatically elevated in the stretched plantaris but not soleus, whereas the MRF4 transcript was significantly elevated in soleus but not plantaris. Levels of myogenin mRNA were unaffected by disuse in either muscle and MRF4 was markedly lower in plantaris in response to disuse.

Animals↗
PubMed1995

The developmental regulation of a novel muscle LIM-protein.

Using a cDNA clone derived from a human muscle library we have identified a novel and highly conserved 2.3kb homologue which is highly expressed in skeletal muscle. The partial sequence contains at least three LIM domains and shows greatest homology with the group of LIM-proteins associated with the cytoskeleton and focal adhesion plaques which include zyxin and paxillin. This homologue is maximally expressed in differentiated ovine primary muscle cultures. It is also expressed in the ovine fetus from at least 50 days of gestation and is increasingly upregulated from 120 days of gestation to 8 weeks after birth after which it declines. This period corresponds to the period of greatest muscle fibre hypertrophy and suggests a role for this homologue in either the elaboration of muscle fibre matrix anchorage or the regulation of muscle fibre hypertrophy itself.

Adolescent↗
PubMed1994

Interactions between growth hormone and nutrition in hypophysectomised rats: skeletal muscle myosin heavy chain mRNA levels.

The aim of this study was to examine the role of growth hormone (GH) in regulating muscle phenotype and to determine how this is modulated by altered nutrition. Total RNA was extracted from gastrocnemius muscles of hypophysectomised rats treated with saline, GH or GH but fed a restricted intake. Type 1, 2A, 2B, embryonic and neonatal myosin heavy chain mRNA levels were estimated by slot blot hybridization. Hypophysectomy reduced the concentrations of types 1, 2A and embryonic mRNAs and dramatically elevated types 2B and neonatal compared to control levels, but this was time-dependent. All MHC mRNA levels were partially restored to control levels in the GH-treated rats except for type 1; the level of this transcript was only elevated by GH in the restricted intake group. Restricted food intake modulated the effects of GH administration for all other MHC mRNA concentrations.

Animal Nutritional Physiological Phenomena↗
PubMed1993

Interactions between growth hormone and nutrition in hypophysectomized rats: body composition and production of insulin-like growth factor-I.

Hypophysectomy of adult rats results in a loss of body growth which can be reversed by treatment with GH. The increased growth caused by administration of GH is accompanied by an increase in food consumption. The effects of GH and interactions with nutrition were investigated by treating hypophysectomized rats with GH and either providing unrestricted food or preventing the increased food consumption by pair-feeding with the same intake as that of the hypophysectomized animals. Over the 7-day experimental period, the GH-treated animals grew significantly when food was available ad libitum but did not gain body weight when an increase in food intake was prevented. However, there was a significant interaction between GH and nutrition on body composition; GH significantly decreased body fat and increased the protein: fat ratio only in the animals with the restricted intake. Gastrocnemius muscle weight was increased by GH regardless of food intake, but heart weight did not increase and liver weight was actually decreased by GH treatment when food intake was restricted. Serum concentrations of insulin and insulin-like growth factor-I (IGF-I) were increased by GH in the rats with food available ad libitum but not in the pair-fed rats. However, the liver concentration of IGF-I and its mRNA were increased by GH although the increase in IGF-I mRNA was modulated by the restricted food intake. The decreased weight of the liver in the pair-fed GH-treated rats, despite the increase in IGF-I mRNA, suggests that IGF-I does not influence liver growth. In the gastrocnemius muscle, however, GH increased IGF-I mRNA concentration similarly in both rats with food available ad libitum and in pair-fed rats. Decreased nutrition therefore modulated the action of GH but emphasized its nutrient partitioning effect, thus increasing the anabolic drive towards skeletal muscle growth; this appeared to be mediated by the local production of IGF-I within the muscle.

Animal Nutritional Physiological Phenomena↗
PubMed1992

Gene expression in skeletal muscle in response to stretch and force generation.

Striated muscle is a tissue in which gene expression is influenced to a large extent by mechanical signals. This includes the regulation of gene expression-associated muscle fiber phenotype determination, which depends on which protein isoform genes are transcribed, as well as muscle fiber mass accretion, which appears to involve some translational regulation. Although muscle synthesizes a set of highly specialized proteins it has a remarkable ability to adapt by expressing different isoforms of the same protein so that it acquires the appropriate contractile characteristics. Our work has focused on the myosin heavy chain (HC) genes as these encode the myosin cross bridge, which is responsible for muscle intrinsic velocity of contraction and economy of force development. RNA analyses after cast immobilization of the limb with the muscle in the lengthened or shortened position and/or with electrical stimulation were used to determine the effects of altered mechanical signals on gene transcription. When the soleus muscle was immobilized in the shortened position in the young animal it did not fully differentiate into a slow postural-type muscle. Even in the adult, the soleus muscle if deprived of stretch and contractile activity switches back to transcribing the fast myosin HC gene. The converse was true when the fast rabbit tibialis anterior was subjected to immobilization in the lengthened position and/or electrical stimulation. Both stretch alone and stimulation alone caused repression of the fast type and activation of the slow myosin genes. The reprogramming of the fast muscle was more complete when the stretch was combined with stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Regulation of insulin-like growth factor 1 gene expression in skeletal muscle.

Insulin-like growth factor 1 (IGF-1) is implicated in the growth processes of many tissues in the adult animal. This hormone can act in an endocrine manner or can be produced in the specific tissues in response to growth promoting stimuli to act in an autocrine/paracrine manner. We have examined, in the rat, changes in serum concentrations of IGF-1 and muscle IGF-1 mRNA levels in several studies in which muscle growth has been significantly altered. In the first study we examined the interactions of growth hormone (GH) and under-nutrition upon muscle growth. We observed that when GH was administered to hypophysectomised rats the anabolic effect of this hormone was independent of dietary intake. In a similar manner muscle IGF-1 mRNA levels were also elevated by GH but unaffected by food intake. In contrast serum IGF-1 levels were markedly reduced by under-nutrition. These data suggested that the anabolic action of GH on muscle could be mediated through the autocrine/paracrine action of the IGF-1 hormone. Similarly we observed in other studies that muscle hypertrophic stimuli of work-overload and passive stretch are associated with significantly increased muscle IGF-1 mRNA levels. In contrast insulin dramatically affected muscle protein synthesis rates but had no measurable effect upon muscle IGF-1 mRNA levels, which suggests that the anabolic action of this hormone is not mediated through the autocrine/paracrine action of IGF-1. These studies suggest that IGF-1 may mediate growth in muscle in response to variety of stimuli by autocrine/paracrine action or in response to certain stimuli possibly by endocrine action.

Animals↗
PubMed1990

Disuse and passive stretch cause rapid alterations in expression of developmental and adult contractile protein genes in skeletal muscle.

Contractile proteins exist as a number of isoforms that show a developmental and tissue-specific pattern of expression. Using gene-specific cDNA probes, the expression of the sarcomeric myosin heavy chain (MHC) multi-gene family and of cardiac (foetal) alpha-actin was analysed in three different rat hindlimb muscles immobilised for 5 days in either the shortened or lengthened positions. For each of the MHC genes normally expressed in adult muscle (slow, IIA and IIB), the effect of disuse alone (immobilisation in the shortened position) upon expression was markedly different to that of passive stretch (immobilisation in the lengthened position) in each of the three muscles. However, the same adult sarcomeric myosin heavy chain gene can be affected in a different, or even opposite, manner by either disuse or passive stretch depending on the muscle in which it is being expressed. The fast IIB MHC gene, for example, exhibits a rapid induction in the slow postural soleus muscle, in response to disuse but no such induction occurs in the faster plantaris and gastrocnemius muscles. Furthermore, the induction of this gene in the soleus was prevented by passive stretch. The MHC gene, normally only expressed in embryonic skeletal muscle, showed a similar response in all three muscles and was reinduced in adult muscle in response to passive stretch but not by disuse alone. In contrast, the isoform of alpha-actin which is normally only present in significant quantities in embryonic skeletal muscle and which is reduced postnatally, is not reinduced by passive stretch but is reduced still further by immobilisation in the shortened position.

Actins↗
PubMed1989

Work overload induced changes in fast and slow skeletal muscle myosin heavy chain gene expression.

Work induced hypertrophy of the slow postural soleus and the fast phasic plantaris muscles was produced by tenotomy of the synergistic gastrocnemius muscle. Increases in weight of both muscles were associated with proportionately even larger increases in total RNA and mRNA levels. Alterations in levels of specific myosin heavy chain (MHC) isoform mRNAs were measured using the slot blot procedure with radioactively labelled oligonucleotides as probes. Type 1 MHC gene expression was unaffected in both muscles by work overload, whereas type 2a was deinduced in the soleus and type 2b was deinduced in the plantaris. The neonatal MHC gene was transiently reinduced in the plantaris.

Animals↗
PubMed1987

Effects of hypokinesia and hypodynamia upon protein turnover in hindlimb muscles of the rat.

Hypokinesia/hypodynamia was induced in the hindlimb muscles of the rat using a suspension technique. This caused differing degrees of atrophy in different muscles, however, this atrophy was reduced in muscles held in a lengthened position. The greatest degree of wasting was observed in the unstretched soleus, a slow postural muscle, where both Type 1 and Type 2a fibers atrophied to the same degree. However, wasting of the gastrocnemius muscle was associated with a reduction in the size of the Type 2b fibers. In both slow postural and fast phasic hindlimb muscles, atrophy was brought about by a reduction in the rate of protein synthesis in conjunction with an elevation in the rate of protein degradation. When inactive muscles were passively stretched, both protein synthesis and degradation were dramatically elevated. Even periods of stretch of as little as 0.5 h.d-1 were found to significantly decrease atrophy in inactive muscles.

Animals↗
PubMed1984

Muscle fiber activity in carp as a function of swimming speed and muscle temperature.

These experiments were performed to determine how ectothermal animals maintain their locomotory ability during acute changes in muscle temperature, despite the large thermal dependence of the mechanical properties of their muscle. The electrical activity of the red (slow-twitch) and white (fast-twitch) muscle fibers of carp was monitored while the carp swam at various speeds at 10 and 20 degrees C. The patterns of recruitment of different fiber types were similar at both temperatures. At low speeds only the red muscle was active, whereas at high speeds the white muscle was active as well. The swimming velocity at which white muscle was initially recruited increased from 26 cm/s at 10 degrees C to 46 cm/s at 20 degrees C. These results suggest that the order of recruitment of motor units was the same at 10 and 20 degrees C but that the recruitment occurred over a narrower range of speeds at the low temperature. Hence, to generate the muscle power required to swim at a certain velocity, fish recruit more muscle fibers, which include faster fiber types when their muscle is cold than when their muscle is warm.

Animals↗
PubMedDate not supplied

Electrical stimulation modulates IGF binding protein transcript levels in C2C12 myotubes.

Electrical stimulation (ES) of skeletal muscle can produce changes in metabolic enzyme and contractile protein gene expression resulting in fast-to-slow phenotypic changes. The molecular mechanism by which ES induces changes in phenotype is not entirely understood but recent reports have demonstrated that the calcineurin/NF-AT signalling pathway is involved. IGF-1 is also capable of inducing changes in phenotype through the same calcineurin/NF-AT pathway but little is known of the direct effect of ES on the IGF system. In this study, we examined the effects of ES on the expression of igf-1, igf-2 and the six igfbp genes in the C2C12 muscle cell line. Results showed that ES induced a change in phenotype that was accompanied by downregulation of igf-2 and upregulation of igfbp-4 mRNA levels. However, ES did not significantly alter the transcription of igf-1, igfbp-2, igfbp-5 and igfbp-6 genes. This study demonstrates that ES of muscle cells in vitro not only directly modulates the gene expression of contractile proteins but also modulates proteins that are part of the IGF regulatory system, in particular IGFBP-4.

Animals↗