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Stephen Welle

Publications and source records attributed to Stephen Welle.

11 recordsLinked to original sources
PubMed2003

Gene expression profile of aging in human muscle.

Studies of gene expression related to aging of skeletal muscle have included few subjects or a limited number of genes. We conducted the present study to produce more comprehensive gene expression profiles. RNA was extracted from vastus lateralis biopsies obtained from healthy young (21-27 yr old, n = 8) and older men (67-75 yr old, n = 8) and was analyzed with high-density oligonucleotide arrays. Of the approximately 44,000 probe sets on the arrays, approximately 18,000 yielded adequate signals for statistical analysis. There were approximately 700 probe sets for which t-tests or rank sum tests indicated a difference (P <or= 0.01) in mean expression between young and old and for which the estimated false discovery rate was <10%. Most of these differences were less than 1.5-fold in magnitude. Genes that encode proteins involved in energy metabolism and mitochondrial protein synthesis were expressed at a lower level in older muscle. Genes encoding metallothioneins, high-mobility-group proteins, heterogeneous nuclear ribonucleoproteins and other RNA binding/processing proteins, and components of the ubiquitin-proteasome proteolytic pathway were expressed at higher levels in older muscle. Expression of numerous genes involved with stress responses, hormone/cytokine/growth factor signaling, control of the cell cycle and apoptosis, and transcriptional regulation appeared to be affected by aging. More transcripts were detected in older muscle, suggesting dedifferentiation, an increased number of splice variants, or increased cellular heterogeneity. We conclude that in human skeletal muscle the expression of many genes tends to increase or decrease between the third and seventh decades. The changes are modest when averaged over all of the cells in the tissue.

Adult↗
PubMed2003

Relative importance of liver, kidney, and substrates in epinephrine-induced increased gluconeogenesis in humans.

Splanchnic and renal net balance measurements indicate that lactate and glycerol may be important precursors for epinephrine-stimulated gluconeogenesis (GNG) in liver and kidney, but the effects of epinephrine on their renal and hepatic conversion to glucose in humans have not yet been reported. We therefore used a combination of renal balance and isotopic techniques in nine postabsorptive volunteers to measure systemic and renal GNG from these precursors before and during a 3-h infusion of epinephrine (270 pmol. kg-1. min-1) and calculated hepatic GNG as the difference between systemic and renal rates. During infusion of epinephrine, renal and hepatic GNG from lactate increased 4- to 6-fold and accounted for approximately 85 and 70% of renal and hepatic glucose release, respectively, at the end of study; renal and hepatic GNG from glycerol increased approximately 1.5- to 2-fold and accounted for approximately 7-9% of renal and hepatic glucose release at the end of study. The increased renal GNG from lactate and glycerol was due not only to their increased renal uptake (approximately 3.3- and 1.4-fold, respectively) but also increased renal gluconeogenic efficiency (approximately 1.8- and 1.5-fold). The increased renal uptake of lactate and glycerol was wholly due to their increased arterial concentrations, since their renal fractional extraction remained unchanged and renal blood flow decreased. We conclude that 1) lactate is the predominant precursor for epinephrine-stimulated GNG in both liver and kidney, 2) hepatic and renal GNG from lactate and glycerol are similarly sensitive to stimulation by epinephrine, and 3) epinephrine increases renal GNG from lactate and glycerol by increasing substrate availability and the gluconeogenic efficiency of the kidney.

Adult↗
PubMed2002

Reduced amount of mitochondrial DNA in aged human muscle.

Muscle concentrations of mRNAs encoded by mitochondrial DNA (mtDNA) decline with aging. To determine whether this can be explained by diminished mtDNA levels, we measured the relative concentrations of mtDNA and a representative mtDNA transcript [encoding cytochrome-c oxidase, subunit 2 (COX-2)] in muscle of young (21-27 yr) and older subjects (65-75 yr). The amount of COX-2 mRNA (relative to 28S rRNA) was 22% lower (P = 0.04) in older muscle, and the amount of mtDNA (relative to nuclear DNA) was 38% lower (P = 0.0002). The average level of mitochondrial transcription factor A (Tfam), a protein essential for mtDNA replication, was similar in younger and older muscle. Tfam mRNA, nuclear respiratory factor-1 mRNA, and several mRNAs encoding proteins required for mtDNA replication were expressed at similar levels in younger and older muscle. The mtDNA concentrations were only weakly related to age-adjusted aerobic fitness (maximal oxygen consumption) and self-reported physical activity levels. We conclude that the lower concentration of mitochondrial mRNAs in older muscle can be explained by a reduced concentration of mtDNA.

Adult↗
PubMed2002

Computational method for reducing variance with Affymetrix microarrays.

BACKGROUND: Affymetrix microarrays are used by many laboratories to generate gene expression profiles. Generally, only large differences (> 1.7-fold) between conditions have been reported. Computational methods to reduce inter-array variability might be of value when attempting to detect smaller differences. We examined whether inter-array variability could be reduced by using data based on the Affymetrix algorithm for pairwise comparisons between arrays (ratio method) rather than data based on the algorithm for analysis of individual arrays (signal method). Six HG-U95A arrays that probed mRNA from young (21-31 yr old) human muscle were compared with six arrays that probed mRNA from older (62-77 yr old) muscle. RESULTS: Differences in mean expression levels of young and old subjects were small, rarely > 1.5-fold. The mean within-group coefficient of variation for 4629 mRNAs expressed in muscle was 20% according to the ratio method and 25% according to the signal method. The ratio method yielded more differences according to t-tests (124 vs. 98 differences at P < 0.01), rank sum tests (107 vs. 85 differences at P < 0.01), and the Significance Analysis of Microarrays method (124 vs. 56 differences with false detection rate < 20%; 20 vs. 0 differences with false detection rate < 5%). The ratio method also improved consistency between results of the initial scan and results of the antibody-enhanced scan. CONCLUSION: The ratio method reduces inter-array variance and thereby enhances statistical power.

Adult↗
PubMed2002

Gene transcript profiling in aging research.

Advances in biotechnology have led to methods for quantifying the relative concentrations of thousands of mRNAs in parallel. While these are powerful methods that can be used for both hypothesis testing and hypothesis generation, gene transcript profiling has some limitations as a tool to study aging. These include the difficulty in separating effects of aging from analytical and biological variability, statistical problems associated with simultaneous determination of so many different gene transcripts, and uncertainty about the functional significance of changes in mRNA concentrations. In this review, these issues are discussed with a focus on two methods for profiling mRNAs--serial analysis of gene expression (SAGE) and DNA arrays.

Aging↗
PubMed2002

Insulin-like growth factor-1 and myostatin mRNA expression in muscle: comparison between 62-77 and 21-31 yr old men.

The present study was done to determine the effect of age on muscle concentrations of mRNAs encoding two growth factors that are thought to be important regulators of muscle mass: insulin-like growth factor-1 (IGF-1) and myostatin. Quantitative RT-PCR assays indicated that the mean IGF-1 mRNA concentration in older muscle (62-77 yr, n=15 men) was approximately 25% less, per ng total RNA (P<0.005), than in young adult muscle (21-31 yr, n=12 men). One third of the older men had IGF-1 mRNA levels below the lowest concentration observed in young muscle. Myostatin mRNA concentrations were similar in young and old muscle. Muscle mass and myofibrillar protein synthesis rates among eight older men did not correlate with either IGF-1 or myostatin mRNA levels. We conclude that IGF-1 gene expression in muscle tends to decline with normal aging. The functional significance is uncertain.

Adult↗
PubMed2002

Exogenous insulin replacement in type 2 diabetes reverses excessive hepatic glucose release, but not excessive renal glucose release and impaired free fatty acid clearance.

In type 2 diabetes renal and hepatic glucose release are increased and free fatty acids (FFA) clearance is reduced. Restoration of normoglycemia by exogenous insulin replacement normalizes overall glucose release and plasma FFA concentrations. However, it is unclear to what extent normalization of overall glucose release is due to suppression of hepatic (HGR) and renal glucose release (RGR) and whether the abnormal FFA clearance is improved. We therefore determined overall, renal, and hepatic glucose release, as well as systemic FFA release and clearance by tracer techniques in type 2 diabetic subjects with (DM(+)) and without (DM(-)) physiologic overnight insulin infusion and in nondiabetic volunteers (NV). Insulin infusion normalized plasma glucose (5.3 +/- 0.1 v 5.2 +/- 0.1 mmol/L in NV) and overall glucose release (10.1 +/- 0.7 v 10.6 +/- 0.4 micromol x kg(-1) x min(-1) in NV), (both P >.9). Values in DM(-) were 9.1 +/- 0.6 mmol/L and 14.6 +/- 0.8 micromol x kg(-1) x min(-1), respectively (both P <.001 v DM(+) and NV). The correction of overall glucose release in DM(+) was due to suppression of HGR to rates below normal (6.11 +/- 0.53 v 8.67 +/- 0.44 micromol x kg(-1) x min(-1) in NV, P <.03). RGR remained increased (3.91 +/- 0.38 v 1.90 +/- 0.28 micromol x kg(-1) x min(-1) in NV, P <.002) and was similar to DM(-) (3.97 +/- 0.33 micromol x kg(-1) x min(-1), P >.9). Insulin infusion also normalized plasma FFA levels (450 +/- 45 v 476 +/- 42 in NV, P >.9 and v613 +/- 33 micromol/L in DM(-), P <.04). This was due to suppression of FFA release to below normal (4.04 +/- 0.45 v 5.25 +/- 0.25 micromol x kg(-1) x min(-1) in NV, P <.04). Plasma FFA clearance remained reduced (7.2 +/- 1.0 v 11.4 +/- 1.2 mL x kg(-1) x min(-1) in NV, P <.04) and was similar to DM(-) (7.3 +/- 0.5 mL x kg(-1) x min(-1), P >.9). We conclude that in contrast to the excessive HGR, excessive RGR and impaired FFA clearance are not corrected by acute exogenous insulin replacement.

Adult↗
PubMed2002

Cellular and molecular basis of age-related sarcopenia.

Sarcopenia, the decline in muscle bulk and performance associated with normal aging, is an important component of frailty in the elderly. The gradual loss of both motor nerves and muscle fibers during senescence appears to be the major problem. Atrophy (especially in fast-twitch fibers) and impaired function of the surviving cells also contribute to sarcopenia. Although skeletal muscle has the capacity to regenerate itself, this process is not activated by the gradual age-related loss of muscle fibers. The endocrine, autocrine, and paracrine environment in old muscle is less supportive of protein synthesis, reinnervation of muscle fibers, and satellite cell activation, proliferation, and differentiation. Lifelong exposure of DNA to free radical damage results in accumulation of somatic mutations in nerves and muscle fibers. Reduced protein synthesis leads to atrophy, and slower fractional protein turnover contributes to longer retention of proteins that may have been damaged by free radicals. Many genes are differentially expressed in young and old muscle, but additional research is needed to determine which of these genes have a significant role in the pathogenesis or adaptation to sarcopenia.

Aging↗
PubMed2002

Renal substrate exchange and gluconeogenesis in normal postabsorptive humans.

Release of glucose by the kidney in postabsorptive normal humans is generally regarded as being wholly due to gluconeogenesis. Although lactate is the most important systemic gluconeogenic precursor and there is appreciable net renal lactate uptake, renal lactate gluconeogenesis has not yet been investigated. The present studies were therefore undertaken to quantitate the contribution of lactate to renal gluconeogenesis and the role of the kidney in lactate metabolism. We determined systemic and renal lactate conversion to glucose as well as renal lactate net balance, fractional extraction, uptake, and release in 24 postabsorptive humans by use of a combination of isotopic and renal balance techniques. For comparative purposes, accumulated similar data for glutamine, alanine, and glycerol are also reported. Systemic lactate gluconeogenesis (1.97 +/- 0.12 micromol x kg(-1) x min(-1)) was about threefold greater than that from glycerol, glutamine, and alanine. The sum of gluconeogenesis from these precursors, uncorrected for tricarboxylic acid (TCA) cycle carbon exchange, explained 34% of systemic glucose release. Renal lactate uptake (3.33 +/- 0.28 micromol x kg(-1) x min(-1)) accounted for nearly 30% of its systemic turnover. Renal gluconeogenesis from lactate (0.78 +/- 0.10 micromol x kg(-1) x min(-1)) was 3.5, 2.5, and 9.6-fold greater than that from glycerol, glutamine, and alanine. The sum of renal gluconeogenesis from these precursors equaled approximately 40% of the sum of their systemic gluconeogenesis. When the isotopically determined rates of systemic and renal gluconeogenesis were corrected for TCA cycle carbon exchange, gluconeogenesis from these precursors accounted for 43% of systemic glucose release and 89% of renal glucose release. We conclude that 1) in postabsorptive normal humans, lactate is the dominant precursor for both renal and systemic gluconeogenesis; 2) the kidney is an important organ for lactate disposal; 3) under these conditions, renal glucose release is predominantly, if not exclusively, due to gluconeogenesis; and 4) liver and kidney are similarly important for systemic gluconeogenesis.

Adult↗