Biomedical subjects

Gregory S Harper

Publications and source records attributed to Gregory S Harper.

4 recordsLinked to original sources

PubMed2006

A gene coexpression network for bovine skeletal muscle inferred from microarray data.

We present the application of large-scale multivariate mixed-model equations to the joint analysis of nine gene expression experiments in beef cattle muscle and fat tissues with a total of 147 hybridizations, and we explore 47 experimental conditions or treatments. Using a correlation-based method, we constructed a gene network for 822 genes. Modules of muscle structural proteins and enzymes, extracellular matrix, fat metabolism, and protein synthesis were clearly evident. Detailed analysis of the network identified groupings of proteins on the basis of physical association. For example, expression of three components of the z-disk, MYOZ1, TCAP, and PDLIM3, was significantly correlated. In contrast, expression of these z-disk proteins was not highly correlated with the expression of a cluster of thick (myosins) and thin (actin and tropomyosins) filament proteins or of titin, the third major filament system. However, expression of titin was itself not significantly correlated with the cluster of thick and thin filament proteins and enzymes. Correlation in expression of many fast-twitch muscle structural proteins and enzymes was observed, but slow-twitch-specific proteins were not correlated with the fast-twitch proteins or with each other. In addition, a number of significant associations between genes and transcription factors were also identified. Our results not only recapitulate the known biology of muscle but have also started to reveal some of the underlying associations between and within the structural components of skeletal muscle.

Adipose Tissue↗

PubMed2006

Gene expression, synthesis and degradation of hyaluronan during differentiation of 3T3-L1 adipocytes.

The high molecular weight glycosaminoglycan hyaluronan (HA) is an essential component of the extracellular matrix (ECM), however, the link between HA regulation and development of the adipocyte ECM, which is essential for differentiation, remains undefined. Hyaluronan synthase gene expression, HA synthetic rate and molecular weight during differentiation of 3T3-L1 pre-adipocytes were compared to undifferentiated 3T3-L1 pre-adipocytes and non-adipogenic NIH/3T3 fibroblasts. In the 3T3-L1 pre-adipocytes, the predominant genes associated with HA metabolism were found to be HA synthase-2 (Has-2) and hyaluronidase-2 (Hyal-2) demonstrating a co-regulation of expression which was stimulated by adipogenic induction consequently resulting in increased synthesis of high molecular weight HA (>10 MDa) and its simultaneous degradation. Accumulation of HA correlated positively with cell number, although synthetic rate was inversely related suggesting a regulatory feedback mechanism. Within 24h post-induction, pre-adipocytes responded with a higher HA synthetic rate and later, accumulated cytoplasmic lipid. In contrast, undifferentiated pre-adipocytes had a reduced HA synthetic rate during clonal expansion and did not accumulate lipid. HA was continuously and rapidly metabolised throughout 3T3-L1 adipogenesis, where terminal differentiation coincided with the increased generation of low molecular weight, angiogenic HA fragments, a likely prerequisite for concurrent neovascularisation of adipose tissue. This study has highlighted a relationship between HA metabolism and adipocyte differentiation, suggesting that the balance between the formation and regulation of the adipocyte extracellular matrix is finely coordinated in a growth phase-specific dependent manner.

3T3-L1 Cells↗

PubMed2005

Lessons from an estivating frog: sparing muscle protein despite starvation and disuse.

Long (6- to 9-mo) bouts of estivation in green-striped burrowing frogs lead to 28% atrophy of cruralis oxidative fibers (P < 0.05) and some impairment of in vitro gastrocnemius endurance (P < 0.05) but no significant deficit in maximal twitch force production. These data suggest the preferential atrophy of oxidative fibers at a rate slower than, but comparable to, laboratory disuse models. We tested the hypothesis that the frog limits atrophy by modulating oxidative stress. We assayed various proteins at the transcript level and verified these results for antioxidant enzymes at the biochemical level. Transcript data for NADH ubiquinone oxidoreductase subunit 1 (71% downregulated, P < 0.05) and ATP synthase (67% downregulated, P < 0.05) are consistent with mitochondrial quiescence and reduced oxidant production. Meanwhile, uncoupling protein type 2 transcription (P = 0.31), which is thought to reduce mitochondrial leakage of reactive oxygen species, was maintained. Total antioxidant defense of water-soluble (22.3 +/- 1.7 and 23.8 +/- 1.5 microM/microg total protein in control and estivator, respectively, P = 0.53) and membrane-bound proteins (31.5 +/- 1.9 and 42.1 +/- 7.3 microM/microg total protein in control and estivator, respectively, P = 0.18) was maintained, equivalent to a bolstering of defense relative to oxygen insult. This probably decelerates muscle atrophy by preventing accumulation of oxidative damage in static protein reserves. Transcripts of the mitochondrially encoded antioxidant superoxide dismutase type 2 (67% downregulated, P < 0.05) paralleled mitochondrial activity, whereas nuclear-encoded catalase and glutathione peroxidase were maintained at control values (P = 0.42 and P = 0.231), suggesting a dissonance between mitochondrial and nuclear antioxidant expression. Pyruvate dehydrogenase kinase 4 transcription was fourfold lower in estivators (P = 0.11), implying that, in contrast to mammalian hibernators, this enzyme does not drive the combustion of lipids that helps spare hypometabolic muscle.

Animals↗

PubMed2005

Transcriptional profiling of skeletal muscle tissue from two breeds of cattle.

We used a 9.6 K cattle muscle/fat cDNA microarray to study gene expression differences between the longuissimus dorsi (LD) muscle of Japanese Black (JB) and Holstein (HOL) cattle. JB cattle exhibit an unusual ability to accumulate intramuscular adipose tissue with fat melting points lower than that in other breeds. The LD biopsies from three JB (Tajima strain) and three HOL animals were used in this breed comparison. Seventeen genes were identified as preferentially expressed in LD samples from JB and seven genes were found to be expressed more highly in HOL. The expression of six selected differentially expressed genes was confirmed by quantitative real-time PCR. The genes more highly expressed in JB are associated with unsaturated fatty acid synthesis, fat deposition, and the thyroid hormone pathway. These results are consistent with the increased amounts and proportions of monounsaturated fatty acids observed in the muscle of JB animals. By discovering as yet uncharacterized genes that are differentially regulated in this comparison, the work may lead us to a better understanding of the regulatory pathways involved in the development of intramuscular adipose tissue.

Animals↗