Mahjabeen Hameed's research while affiliated with University College London and other places
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Publications (10)
Elevated growth hormone (GH) levels lead to increased circulating insulin-like growth factor-I (IGF-I), but the effects on localised muscle IGF-I splice variant expression is not known. The effects of rhGH administration, with or without an acute bout of high resistance exercise, were measured on serum IGF-I and on the mRNA levels of IGF-I splice v...
Recovery from micro damage resulting from intensive exercise has been shown to take longer in older muscles. To investigate the factors that may contribute to muscle repair, we have studied the expression of two splice variants of the insulin-like growth factor-I (IGF-I) gene. IGF-IEa and mechano growth factor (MGF) were studied in response to 1 h...
IntroductionGrowth hormone-IGF-I axisExpression of IGF-I splice variants in muscleMechano growth factorSystemic IGF-I is produced by active muscleThe structure of IGF-IReceptors mediate the cellular effects of IGF-IIGF-I binding proteinsBiological action of the IGF-I splice variantsGenetic manipulation of IGF-I in muscleGene transfer of the differe...
Little is known about the expression of skeletal muscle-specific isoforms of the insulin-like growth factor-I (IGF-I) gene in response to exercise in humans. Data for women are sparse and the influences of age and physical training status are unknown. Here we aimed to describe the expression of mRNA for the IGF-I isoforms in the quadriceps muscles...
Studies in animals and human muscle have demonstrated differential splicing of the insulin-like growth factor-1 gene in response to mechanical strain and damage. We conducted a study on the expression of insulin-like growth factor-1 splice variants in the levator ani muscle after the first vaginal delivery.
Ten women were recruited after the first...
The expression of two isoforms of insulin-like growth factor-I (IGF-I): mechano growth factor (MGF) and IGF-IEa were studied in muscle in response to growth hormone (GH) administration with and without resistance training in healthy elderly men. A third isoform, IGF-IEb was also investigated in response to resistance training only. The subjects (ag...
Journal of Physiology547, 247–254 (2003)
The mRNA expression of two splice variants of the insulin-like growth factor-I (IGF-I) gene, IGF-IEa and mechano growth factor (MGF), were studied in human skeletal muscle. Subjects (eight young, aged 25-36 years, and seven elderly, aged 70-82 years) completed 10 sets of six repetitions of single legged knee extensor exercise at 80 % of their one r...
Sarcopenia is the loss of muscle mass associated with the aging process. Although systemic or circulating growth hormone and insulin-like growth factor-1 levels fall as we age, this is likely to be of lesser importance in regard to muscle mass than the role of locally produced insulin-like growth factor-1s generated in the muscle in response to exe...
Citations
... It thus appears that ageing was associated with impairment in this potentially important local mechanism of muscle growth and repair. Preliminary data on older men indicate that they are also less well able to up-regulate this isoform following leg extensor weightlifting exercise (Hameed, Orrell, Cobbold, Goldspink, Harridge, 2002). If MGF is important as a local repair factor, then these data would be in general agreement with the work of Faulkner and colleagues. ...
Reference: Ageing and local growth factors in muscle
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... Essa isoforma, denominada MGF (mechano growth factor), é expressa quando o músculo é sub metido à sobrecarga (GOLDSPINK, 2003), ou seja, sendo regulada por sinais mecânicos. A isoforma hepática, que também é produzida pelo músculo, é denominada IGF-1Ea (GOLDSPINK et al., 2006). ...
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... 26,27 However, both promoters are probably not mutually exclusive, and GH can also stimulate the tissue-specific (local form) transcripts expression, although the present evidence is still ambiguous. [28][29][30][31][32][33] Alternative splicing at 3'end of the Igf1 gene also results in distinct transcripts that contain exon 5, generally are designated as IGF-I Eb, or exon 6 termed as IGF-I Ea, or both exon 5 and 6 as the IGF-I Ec (corresponding to IGF-I Eb in rodents). 18, [34][35][36] Additionally, differential usage of polyadenylation sites further creates size heterogeneity of human IGF-I mRNAs, ranging from 1.1 to 7.6 kb in size. ...
... A commonly postulated mechanism is that greater drug toxicity results in decreased treatment tolerance and reduction in effective drug doses (15,40). Another potential explanation is that decreased levels of insulin-like growth factor-1 (IGF-1) are secreted by the smaller skeletal muscle and that both insulin-like growth factor-1 receptor (IGF-1R) density and signaling are impaired in the aged skeletal muscle (41). Recent studies have suggested that the IGF-1/IGF-1R signaling pathway may contribute to the progression of DLBCL and other cancers (42)(43)(44). ...
... However, total IGF-I, IGFBP-3, and ALS were unchanged over 24 hours of recovery after moderate-or long-duration aerobic (45 or 90 minutes) or resistance (1 or 2 hours) exercise (431). These findings should not discount the role of autocrine or paracrine effects of IGF-I and MGF given their established stimulation of muscle anabolism (424) and evidence of local expression and production in response to muscle contraction (425,432,433). Similarly, there was no deleterious effect of either the systemic absence of IGF-I (434) or the absence of a local functional IGF-IR (435) on overload-induced muscle hypertrophy. ...
... Mechano growth factor (MGF), a splice variant of the IGF-1 gene, is supposed to be an important local factor promoting satellite cell proliferation in muscle. Although short-term (5-week) resistance exercise failed to increase expression of MGF in elderly as compared to young individuals [60], longer-term training of 12-weeks was still able to upregulate expression of this factor in the elderly [61]. Exercise training can stimulate the GH-IGF-1 axis as well as MGF in the elderly, albeit somewhat less so in older as compared to younger individuals. ...
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... Mechano growth factor (MGF) is a unique, spliced variant of insulin-like growth factor 1 (IGF-1). The IGF-1 gene includes 6 exons and generates 5 distinct mRNAs coding for three distinct isoforms: IGF-1Ea, IGF-1Eb and IGF-1Ec through alternative mRNA splicing [8,9]. IGF-1 is found in various tissues in the body including liver and muscle. ...
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... In the process of muscle repair, high expression of MGF occurs first in satellite cells and in proliferating myoblasts among the IGF family, while IGF-1a and IGF-2 are found during muscle fibre formation [1,94]. In resting muscle, MGF is rapidly induced by stretching or strenuous physical activity, and the basal expression of the MGF isoform is approximately one order of magnitude lower in females than in males [95]. In active muscle, passive stretching increases MGF mRNA expression, and enhanced MGF expression is observed upon treatment with electric stimuli at 10 Hz [1,2]. ...
... Evidence suggests that IGF-1Ec mRNA expression increases 2-2.5 h after exercise [40,43] in young subjects, while older subjects show no change at either time point [43,44]. Therefore, age appears to influence the expression of IGF-1Ec. ...
