Global gene expression profiles in skeletal muscle of monozygotic female twins discordant for hormone replacement therapy

An integrated study of hormone-related sarcopenia for modeling and comparative transcriptome in rats

Sarcopenia is a senile disease with high morbidity, serious complications and limited clinical treatments. Menopause increases the risk of sarcopenia in females, while the exact pathogenesis remains unclear. To systematically investigate the development of hormone-related sarcopenia, we established a model of sarcopenia by ovariectomy and recorded successive characteristic changes. Furthermore, we performed the transcriptome RNA sequencing and bioinformatics analysis on this model to explore the underlying mechanism. In our study, we identified an integrated model combining obesity, osteoporosis and sarcopenia. Functional enrichment analyses showed that most of the significantly enriched pathways were down-regulated and closely correlated with endocrine and metabolism, muscle dysfunction, cognitive impairment and multiple important signaling pathways. We finally selected eight candidate genes to verify their expression levels. These findings confirmed the importance of estrogen in the maintenance of skeletal muscle function and homeostasis, and provided potential targets for further study on hormone-related sarcopenia.

Gender-affirming hormone therapy induces specific DNA methylation changes in blood

Background

DNA methylation is an epigenetic mark that is influenced by underlying genetic profile, environment, and ageing. In addition to X-linked DNA methylation, sex-specific methylation patterns are widespread across autosomal chromosomes and can be present from birth or arise over time. In individuals where gender identity and sex assigned at birth are markedly incongruent, as in the case of transgender people, feminization or masculinization may be sought through gender-affirming hormone therapy (GAHT). GAHT is a cornerstone of transgender care, yet no studies to date have investigated its effect on genome-wide methylation. We profiled genome-wide DNA methylation in blood of transgender women (n = 13) and transgender men (n = 13) before and during GAHT (6 months and 12 months into feminizing or masculinizing hormone therapy).

Results

We identified several thousand differentially methylated CpG sites (DMPs) (Δβ ≥ 0.02, unadjusted p value < 0.05) and several differentially methylated regions (DMRs) in both people undergoing feminizing and masculinizing GAHT, the vast majority of which were progressive changes over time. X chromosome and sex-specific autosomal DNA methylation patterns established in early development are largely refractory to change in association with GAHT, with only 3% affected (Δβ ≥ 0.02, unadjusted p value < 0.05). The small number of sex-specific DMPs that were affected by GAHT were those that become sex-specific during the lifetime, known as sex-and-age DMPs, including DMRs in PRR4 and VMP1 genes. The GAHT-induced changes at these sex-associated probes consistently demonstrated a shift towards the methylation signature of the GAHT-naïve opposite sex, and we observed enrichment of previously reported adolescence-associated methylation changes.

Conclusion

We provide evidence for GAHT inducing a unique blood methylation signature in transgender people. This study advances our understanding of the complex interplay between sex hormones, sex chromosomes, and DNA methylation in the context of immunity. We highlight the need to broaden the field of ‘sex-specific’ immunity beyond cisgender males and cisgender females, as transgender people on GAHT exhibit a unique molecular profile.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-022-01236-4.

Sexual Dimorphism in Innate Immunity: The Role of Sex Hormones and Epigenetics

Sexual dimorphism refers to differences between biological sexes that extend beyond sexual characteristics. In humans, sexual dimorphism in the immune response has been well demonstrated, with females exhibiting lower infection rates than males for a variety of bacterial, viral, and parasitic pathogens. There is also a substantially increased incidence of autoimmune disease in females compared to males. Together, these trends indicate that females have a heightened immune reactogenicity to both self and non-self-molecular patterns. However, the molecular mechanisms driving the sexually dimorphic immune response are not fully understood. The female sex hormones estrogen and progesterone, as well as the male androgens, such as testosterone, elicit direct effects on the function and inflammatory capacity of immune cells. Several studies have identified a sex-specific transcriptome and methylome, independent of the well-described phenomenon of X-chromosome inactivation, suggesting that sexual dimorphism also occurs at the epigenetic level. Moreover, distinct alterations to the transcriptome and epigenetic landscape occur in synchrony with periods of hormonal change, such as puberty, pregnancy, menopause, and exogenous hormone therapy. These changes are also mirrored by changes in immune cell function. This review will outline the evidence for sex hormones and pregnancy-associated hormones as drivers of epigenetic change, and how this may contribute to the sexual dimorphism. Determining the effects of sex hormones on innate immune function is important for understanding sexually dimorphic autoimmune diseases, sex-specific responses to pathogens and vaccines, and how innate immunity is altered during periods of hormonal change (endogenous or exogenous).

Mitochondrial Sirtuin 3: New emerging biological function and therapeutic target

Sirtuin 3 (SIRT3) is one of the most prominent deacetylases that can regulate acetylation levels in mitochondria, which are essential for eukaryotic life and inextricably linked to the metabolism of multiple organs. Hitherto, SIRT3 has been substantiated to be involved in almost all aspects of mitochondrial metabolism and homeostasis, protecting mitochondria from a variety of damage. Accumulating evidence has recently documented that SIRT3 is associated with many types of human diseases, including age-related diseases, cancer, heart disease and metabolic diseases, indicating that SIRT3 can be a potential therapeutic target. Here we focus on summarizing the intricate mechanisms of SIRT3 in human diseases, and recent notable advances in the field of small-molecule activators or inhibitors targeting SIRT3 as well as their potential therapeutic applications for future drug discovery.

Design and protocol of Estrogenic Regulation of Muscle Apoptosis (ERMA) study with 47 to 55-year-old women's cohort: novel results show menopause-related differences in blood count

Supplemental Digital Content is available in the text

Objective:

The multidisciplinary Estrogenic Regulation of Muscle Apoptosis (ERMA) study was designed to reveal how hormonal differences over the menopausal stages affect the physiological and psychological functioning of middle-aged women. This paper describes the protocol and nonrespondent analysis of ERMA and novel findings on menopausal differences in blood count variables and their association with female sex hormones.

Methods:

Women aged 47 to 55 years were assigned to pre, early peri, late peri, and postmenopausal groups based on follicle-stimulating hormone (FSH) and bleeding diary. Multivariate linear regression models were constructed to estimate the association of 17β-estradiol (E₂) and FSH with the blood count variables.

Results:

In all, 3,064 women returned the prequestionnaire (ERMA phase one), 1,393 donated blood samples and were assigned to the relevant menopausal group (phase two), and 914 completed phase three, which included physiological and psychological measurements. Nonrespondents were more likely than respondents to be obese, whereas the menopausal groups showed no mean differences in body mass index. Blood count variables, while being within clinical reference values, showed significant differences between groups. E₂ and FSH were associated with the white blood cell (WBC) count and neutrophil-to-lymphocyte ratio.

Conclusions:

The ERMA study was successful in recruiting and characterizing the menopausal status of a cohort sample of middle-aged women. The significant group differences found in the blood count variables and their associations with E₂ and FSH verifies menopause-associated changes in WBC composition potentially being an early sign of low-grade inflammation that may develop later in life.

17β-estradiol alters mRNA co-expression after murine muscle injury and mild hypobaria

Here, we assessed the effects of 17β-estradiol exposure on mRNA co-expression patterns of muscle tissue during recovery in a closed muscle crush injury and hypobaria exposure murine model. Eighteen ovariectomized placebo-treated and 18 ovariectomized 17β-estradiol-treated female mice underwent closed muscle crush injury and hypobaric simulated flight. The mice recovered for 32, 96, or 192 h, and then were euthanized. Their harvested injured lateral gastrocnemius muscles underwent microarray analysis. We used weighted gene co-expression network analysis to construct a co-expression network for the control mice, and then applied the same network to the estrogen-treated mice. We compared the relationships between co-expression in gene modules over time between the two experimental groups. Enriched functional cluster analyses of significant co-expression network modules document a variety of different pathways of interest. Some of the functional cluster enrichments within several of the significantly correlated modules are related to the formation and function of microtubules. Our findings demonstrate that following a closed muscle crush injury in a murine model, the presence of 17β-estradiol alters mRNA co-expression patterns over time. It appears that estrogen promotes the expression of mRNA related to microtubule activity within the cytoskeleton of myofibers and in movement of organelles and receptors. Further study is needed, but the enrichment of these microtubule-related pathways may be integral in the muscle tissue regeneration process, and thus suggests that the presence of estrogen may promote muscle recovery through the work of the microtubules.

Impact statement

This study uses a murine model to address the clinical situation of transporting soldiers or civilians who have sustained skeletal muscle trauma by air. Our findings show that crush-injured muscle tissue of ovariectomized, 17β-estradiol-treated mice exposed to mild hypobaric hypoxia exhibited mRNA co-expression patterns among pathways associated with microtubule-dependent processes. Palmitoylation and other pathways necessary for movement of estrogen receptors to the cell membrane were also differentially enriched in the estrogen-treated mice. These first findings reframe the discussion regarding estrogen effects during muscle recovery from an inflammation-oriented inquiry to that of a structural, cytoskeletal inquiry and support additional research to understand the non-inflammation-related influences of estrogen during muscle recovery. Also, these results may suggest a role for estrogen or estrogen-like substances to treat muscle trauma.

The Older Finnish Twin Cohort - 45 Years of Follow-up

The older Finnish Twin Cohort (FTC) was established in 1974. The baseline survey was in 1975, with two follow-up health surveys in 1981 and 1990. The fourth wave of assessments was done in three parts, with a questionnaire study of twins born during 1945-1957 in 2011-2012, while older twins were interviewed and screened for dementia in two time periods, between 1999 and 2007 for twins born before 1938 and between 2013 and 2017 for twins born in 1938-1944. The content of these wave 4 assessments is described and some initial results are described. In addition, we have invited twin-pairs, based on response to the cohortwide surveys, to participate in detailed in-person studies; these are described briefly together with key results. We also review other projects based on the older FTC and provide information on the biobanking of biosamples and related phenotypes.

Aging of the musculoskeletal system: How the loss of estrogen impacts muscle strength

Skeletal muscle weakness occurs with aging and in females this is compounded by the loss of estrogen with ovarian failure. Estrogen deficiency mediates decrements in muscle strength from both inadequate preservation of skeletal muscle mass and decrements in the quality of the remaining skeletal muscle. Processes and components of skeletal muscle that are affected by estrogens are beginning to be identified. This review focuses on mechanisms that contribute to the loss of muscle force generation when estrogen is low in females, and conversely the maintenance of strength by estrogen. Evidence is accumulating that estrogen deficiency induces apoptosis in skeletal muscle contributing to loss of mass and thus strength. Estrogen sensitive processes that affect quality, i.e., force generating capacity of muscle, include myosin phosphorylation and satellite cell function. Further detailing these mechanisms and identifying additional mechanisms that underlie estrogenic effects on skeletal muscle is important foundation for the design of therapeutic strategies to minimize skeletal muscle pathologies, such as sarcopenia and dynapenia.

Biological clocks and physical functioning in monozygotic female twins

Background

Biomarkers of biological aging – DNA methylation age (DNAm age) and leukocyte telomere length (LTL)– correlate strongly with chronological age across the life course. It is, however, unclear how these measures of cellular wear and tear are associated with muscle strength and functional capacity, which are known to decline with older age and are associated with mortality. We investigated if DNAm age and LTL were associated with body composition and physical functioning by examining 48 monozygotic twin sisters.

Methods

White blood cell DNAm age (predicted years) was calculated from Illumina 450 k BeadChip methylation data using an online calculator. DNAm age acceleration was defined from the residuals derived from a linear regression model of DNAm age on chronological age. LTL was measured by qPCR. Total body percentage of fat and lean mass were estimated using bioimpedance. Physical functioning was measured by grip strength, knee extension strength and by 10 m maximal walking speed test.

Results

In all participants, DNAm age (58.4 ± 6.6) was lower than chronological age (61.3 ± 5.9 years). Pairwise correlations of monozygotic co-twins were high for DNAm age (0.88, 95% CI 0.79, 0.97), age acceleration (0.68, 95% CI 0.30, 0.85) and LTL (0.77, 95% CI 0.60, 0.94). Increased age acceleration i.e. faster epigenetic aging compared to chronological age was associated with lower grip strength (β = − 5.3 SE 1.9 p = 0.011), but not with other measures of physical functioning or body composition. LTL was not associated with body composition or physical functioning.

Conclusions

To conclude, accelerated DNAm age is associated with lower grip strength, a biomarker known to be associated with physiological aging, and which predicts decline in physical functioning and mortality. Further studies may clarify whether epigenetic aging explains the decline in muscle strength with aging or whether DNAm age just illustrates the progress of aging.

Electronic supplementary material

The online version of this article (10.1186/s12877-018-0775-6) contains supplementary material, which is available to authorized users.

Identification of a T cell gene expression clock obtained by exploiting a MZ twin design

Many studies investigated age-related changes in gene expression of different tissues, with scarce agreement due to the high number of affecting factors. Similarly, no consensus has been reached on which genes change expression as a function of age and not because of environment. In this study we analysed gene expression of T lymphocytes from 27 healthy monozygotic twin couples, with ages ranging over whole adult lifespan (22 to 98 years). This unique experimental design allowed us to identify genes involved in normative aging, which expression changes independently from environmental factors. We obtained a transcriptomic signature with 125 genes, from which chronological age can be estimated. This signature has been tested in two datasets of same cell type hybridized over two different platforms, showing a significantly better performance compared to random signatures. Moreover, the same signature was applied on a dataset from a different cell type (human muscle). A lower performance was obtained, indicating the possibility that the signature is T cell-specific. As a whole our results suggest that this approach can be useful to identify age-modulated genes.

Leukocyte and Skeletal Muscle Telomere Length and Body Composition in Monozygotic Twin Pairs Discordant for Long-term Hormone Replacement Therapy

Estrogen-based hormone replacement therapy (HRT) may be associated with deceleration of cellular aging. We investigated whether long-term HRT has effects on leukocyte (LTL) or mean and minimum skeletal muscle telomere length (SMTL) in a design that controls for genotype and childhood environment. Associations between telomeres, body composition, and physical performance were also examined. Eleven monozygotic twin pairs (age 57.6 ± 1.8 years) discordant for HRT were studied. Mean duration of HRT use was 7.3 ± 3.7 years in the user sister, while their co-twins had never used HRT. LTL was measured by qPCR and SMTLs by southern blot. Body and muscle composition were estimated by bioimpedance and computed tomography, respectively. Physical performance was measured by jumping height and grip strength. HRT users and non-users did not differ in LTL or mean or minimum SMTL. Within-pair correlations were high in LTL (r = 0.69, p = .020) and in mean (r = 0.74, p = .014) and minimum SMTL (r = 0.88, p = .001). Body composition and performance were better in users than non-users. In analyses of individuals, LTL was associated with BMI (r 2 = 0.30, p = .030), percentage total body (r 2 = 0.43, p = .014), and thigh (r 2 = 0.55, p = .004) fat, while minimum SMTL was associated with fat-free mass (r 2 = 0.27, p = .020) and thigh muscle area (r 2 = 0.42, p = .016). We found no associations between HRT use and telomere length. Longer LTLs were associated with lower total and regional fat, while longer minimum SMTLs were associated with higher fat-free mass and greater thigh muscle area. This suggests that telomeres measured from different tissues may have different associations with measures of body composition.

Hormone Replacement Therapy Associated White Blood Cell DNA Methylation and Gene Expression are Associated With Within-Pair Differences of Body Adiposity and Bone Mass

The loss of estrogen during menopause causes changes in the female body, with wide-ranging effects on health. Estrogen-containing hormone replacement therapy (HRT) leads to a relief of typical menopausal symptoms, benefits bone and muscle health, and is associated with tissue-specific gene expression profiles. As gene expression is controlled by epigenetic factors (including DNA methylation), many of which are environmentally sensitive, it is plausible that at least part of the HRT-associated gene expression is due to changes in DNA methylation profile. We investigated genome-wide DNA methylation and gene expression patterns of white blood cells (WBCs) and their associations with body composition, including muscle and bone measures of monozygotic (MZ) female twin pairs discordant for HRT. We identified 7,855 nominally significant differentially methylated regions (DMRs) associated with 4,044 genes. Of the genes with DMRs, five (ACBA1, CCL5, FASLG, PPP2R2B, and UHRF1) were also differentially expressed. All have been previously associated with HRT or estrogenic regulation, but not with HRT-associated DNA methylation. All five genes were associated with bone mineral content (BMC), and ABCA1, FASLG, and UHRF1 were also associated with body adiposity. Our study is the first to show that HRT associates with genome-wide DNA methylation alterations in WBCs. Moreover, we show that five differentially expressed genes with DMRs associate with clinical measures, including body fat percentage, lean body mass, bone mass, and blood lipids. Our results indicate that at least part of the known beneficial HRT effects on body composition and bone mass may be regulated by DNA methylation associated alterations in gene expression in circulating WBCs.

Intramuscular sex steroid hormones are associated with skeletal muscle strength and power in women with different hormonal status

Estrogen (E₂)-responsive peripheral tissues, such as skeletal muscle, may suffer from hormone deficiency after menopause potentially contributing to the aging of muscle. However, recently E₂ was shown to be synthesized by muscle and its systemic and intramuscular hormone levels are unequal. The objective of the study was to examine the association between intramuscular steroid hormones and muscle characteristics in premenopausal women (n = 8) and in postmenopausal monozygotic twin sister pairs (n = 16 co-twins from eight pairs) discordant for the use of E₂-based hormone replacement. Isometric skeletal muscle strength was assessed by measuring knee extension strength. Explosive lower body muscle power was assessed as vertical jump height. Due to sequential nature of enzymatic conversion of biologically inactive dehydroepiandrosterone (DHEA) to testosterone (T) and subsequently to E₂ or dihydrotestosterone (DHT), separate linear regression models were used to estimate the association of each hormone with muscle characteristics. Intramuscular E₂, T, DHT, and DHEA proved to be significant, independent predictors of strength and power explaining 59–64% of the variation in knee extension strength and 80–83% of the variation of vertical jumping height in women (P < 0.005 for all models). The models were adjusted for age, systemic E₂, and total body fat mass. The statistics used took into account the lack of statistical independence of twin sisters. Furthermore, muscle cells were shown to take up and actively synthesize hormones. Present study suggests intramuscular sex steroids to associate with strength and power regulation in female muscle providing novel insight to the field of muscle aging.

Estrogen influences on neuromuscular function in postmenopausal women

Exposure to ovarian sex steroids during different life phases has long-term effects on women's health and wellbeing. Menopause is characterized by rapid decline in ovarian sex steroids already during mid-life, between the ages of 46 and 52. Due to the menopause-related hormonal changes, women in most western countries live more than one-third of their lives in postmenopausal status. The role of ovarian steroids on neuromuscular function in middle-aged and older women has been investigated since the 1980s with increasing volume of research during the last decades. This review considers how different components of the neuromuscular system may be influenced by estrogens and so affects neuromuscular function in postmenopausal women. The main focus is on muscle strength and power, which are closely associated with mobility and functional capacity among older populations. In the end of the review, we summarize recent findings on the underlying biological mechanisms in skeletal muscle that could explain the association between hormone replacement therapy and neuromuscular function among postmenopausal women.

Circulating miR-21, miR-146a and Fas ligand respond to postmenopausal estrogen-based hormone replacement therapy--a study with monozygotic twin pairs

Biological aging is associated with physiological deteriorations, which are partly due to changes in the hormonal profile. MicroRNAs regulate various processes associated with cell senescence; differentiation, replication and apoptosis. Serum microRNAs have potential to serve as noninvasive markers for diagnostics/prognostics and therapeutic targets. We analysed the association of estrogen-based hormone replacement therapy (HRT) with selected microRNAs and inflammation markers from the serum, leukocytes and muscle biopsy samples from 54 to 62 year-old postmenopausal monozygotic twins (n=11 pairs) discordant for HRT usage. Premenopausal 30-35 year-old women (n=8) were used as young controls. We focused on the hormonal aging and on the interaction between HRT use and the modulation of miR-21, miR-146a and classical inflammation markers. Fas-ligand was analysed since it functions in both apoptosis and inflammation. The inflammatory profile was healthier among the premenopausal women compared to the postmenopausal twins. Serum miR-21 and miR-146a levels and FasL concentrations were lower in HRT users compared to their non-using co-twins, demonstrating their responsiveness to HRT. Based on the pairwise FasL analysis, FasL concentration is likely to be genetically controlled. Overall, we suggest that postmenopausal estrogen deficiency sustains the development of "inflamm-aging". Estrogen sensitive, specific circulating microRNAs could be potential, early biomarkers for age-associated physiological deteriorations.

Gene-based association identifies SPATA13-AS1 as a pharmacogenomic predictor of inhaled short-acting beta-agonist response in multiple population groups

Inhaled short-acting beta-agonist (SABA) medication is commonly used in asthma patients to rapidly reverse airway obstruction and improve acute symptoms. We performed a genome wide association study of SABA medication response using gene-based association tests. A linear mixed model approach was first used for SNP associations, and results were later combined using GATES to generate gene-based associations. Our results identified SPATA13-AS1 as being significantly associated with SABA bronchodilator response in 328 healthy African Americans. In replication, this gene was associated with SABA response among 2 separate groups of African Americans with asthma (n=1,073, p=0.011 and n=1,968, p=0.014), 149 healthy African Americans (p=0.003), and 556 European Americans with asthma (p=0.041). SPATA13-AS1 was also associated with longitudinal SABA medication usage in 2 separate groups of African Americans with asthma (n=658, p=0.047 and n=1,968, p=0.025). Future studies are needed to delineate the precise mechanism by which SPATA13-AS1 may influence SABA response.

Gender differences in skeletal muscle substrate metabolism - molecular mechanisms and insulin sensitivity

It has become increasingly apparent that substrate metabolism is subject to gender-specific regulation, and the aim of this review is to outline the available evidence of molecular gender differences in glucose and lipid metabolism of skeletal muscle. Female sex has been suggested to have a favorable effect on glucose homeostasis, and the available evidence from hyperinsulinemic-euglycemic clamp studies is summarized to delineate whether there is a gender difference in whole-body insulin sensitivity and in particular insulin-stimulated glucose uptake of skeletal muscle. Whether an eventual higher insulin sensitivity of female skeletal muscle can be related to gender-specific regulation of molecular metabolism will be topic for discussion. Gender differences in muscle fiber type distribution and substrate availability to and in skeletal muscle are highly relevant for substrate metabolism in men and women. In particular, the molecular machinery for glucose and fatty acid oxidative and storage capacities in skeletal muscle and its implications for substrate utilization during metabolic situations of daily living are discussed, emphasizing their relevance for substrate choice in the fed and fasted state, and during periods of physical activity and recovery. Together, handling of carbohydrate and lipids and regulation of their utilization in skeletal muscle have implications for whole-body glucose homeostasis in men and women. 17-β estradiol is the most important female sex hormone, and the identification of estradiol receptors in skeletal muscle has opened for a role in regulation of substrate metabolism. Also, higher levels of circulating adipokines as adiponectin and leptin in women and their implications for muscle metabolism will be considered.

Estrogen replacement and skeletal muscle: mechanisms and population health

There is a growing body of information supporting the beneficial effects of estrogen and estrogen-based hormone therapy (HT) on maintenance and enhancement of muscle mass, strength, and connective tissue. These effects are also evident in enhanced recovery from muscle atrophy or damage and have significant implications particularly for the muscular health of postmenopausal women. Evidence suggests that HT will also help maintain or increase muscle mass, improve postatrophy muscle recovery, and enhance muscle strength in aged females. This is important because this population, in particular, is at risk for a rapid onset of frailty. The potential benefits of estrogen and HT relative to skeletal muscle function and composition combined with other health-related enhancements associated with reduced risk of cardiovascular events, overall mortality, and metabolic dysfunction, as well as enhanced cognition and bone health cumulate in a strong argument for more widespread and prolonged consideration of HT if started proximal to menopausal onset in most women. Earlier reports of increased health risks with HT use in postmenopausal women has led to a decline in HT use. However, recent reevaluation regarding the health effects of HT indicates a general lack of risks and a number of significant health benefits of HT use when initiated at the onset of menopause. Although further research is still needed to fully delineate its mechanisms of action, the general use of HT by postmenopausal women, to enhance muscle mass and strength, as well as overall health, with initiation soon after the onset of menopause should be considered.

Hormone replacement therapy improves contractile function and myonuclear organization of single muscle fibres from postmenopausal monozygotic female twin pairs

Ageing is associated with a decline in muscle mass and strength leading to increased physical dependency in old age. Postmenopausal women experience a greater decline than men of similar age in parallel with the decrease in female sex steroid hormone production. We recruited six monozygous female twin pairs (55-59 years old) where only one twin pair was on hormone replacement therapy (HRT use = 7.8 ± 4.3 years) to investigate the association of HRT with the cytoplasmic volume supported by individual myonuclei (myonuclear domain (MND) size,) together with specific force at the single fibre level. HRT use was associated with a significantly smaller (∼27%; P < 0.05) mean MND size in muscle fibres expressing the type I but not the IIa myosin heavy chain (MyHC) isoform. In comparison to non-users, higher specific force was recorded in HRT users both in muscle fibres expressing type I (∼27%; P < 0.05) and type IIa (∼23%; P < 0.05) MyHC isoforms. These differences were fibre-type dependent, i.e. the higher specific force in fast-twitch muscle fibres was primarily caused by higher force per cross-bridge while slow-twitch fibres relied on both a higher number and force per cross-bridge. HRT use had no effect on fibre cross-sectional area (CSA), velocity of unloaded shortening (V0) and relative proportion of MyHC isoforms. In conclusion, HRT appears to have significant positive effects on both regulation of muscle contraction and myonuclei organization in postmenopausal women.

Microarray analysis reveals novel features of the muscle aging process in men and women

To develop a global view of muscle transcriptional differences between older men and women and sex-specific aging, we obtained muscle biopsies from the biceps brachii of young and older men and women and profiled the whole-genome gene expression using microarray. A logistic regression-based method in combination with an intensity-based Bayesian moderated t test was used to identify significant sex- and aging-related gene functional groups. Our analysis revealed extensive sex differences in the muscle transcriptome of older individuals and different patterns of transcriptional changes with aging in men and women. In older women, we observed a coordinated transcriptional upregulation of immune activation, extracellular matrix remodeling, and lipids storage; and a downregulation of mitochondrial biogenesis and function and muscle regeneration. The effect of aging results in sexual dimorphic alterations in the skeletal muscle transcriptome, which may modify the risk for developing musculoskeletal and metabolic diseases in men and women.

The genetic pleiotropy of musculoskeletal aging

Musculoskeletal aging is detrimental to multiple bodily functions and starts early, probably in the fourth decade of an individual's life. Sarcopenia is a health problem that is expected to only increase as a greater portion of the population lives longer; prevalence of the related musculoskeletal diseases is similarly expected to increase. Unraveling the biological and biomechanical associations and molecular mechanisms underlying these diseases represents a formidable challenge. There are two major problems making disentangling the biological complexity of musculoskeletal aging difficult: (a) it is a systemic, rather than "compartmental," problem, which should be approached accordingly, and (b) the aging per se is neither well defined nor reliably measurable. A unique challenge of studying any age-related condition is a need of distinguishing between the "norm" and "pathology," which are interwoven throughout the aging organism. We argue that detecting genes with pleiotropic functions in musculoskeletal aging is needed to provide insights into the potential biological mechanisms underlying inter-individual differences insusceptibility to the musculoskeletal diseases. However, exploring pleiotropic relationships among the system's components is challenging both methodologically and conceptually. We aimed to focus on genetic aspects of the cross-talk between muscle and its "neighboring" tissues and organs (tendon, bone, and cartilage), and to explore the role of genetics to find the new molecular links between skeletal muscle and other parts of the "musculoskeleton." Identification of significant genetic variants underlying the musculoskeletal system's aging is now possible more than ever due to the currently available advanced genomic technologies. In summary, a "holistic" genetic approach is needed to study the systems's normal functioning and the disease predisposition in order to improve musculoskeletal health.

Tissue-Specific Effects of Loss of Estrogen during Menopause and Aging

The roles of estrogens have been best studied in the breast, breast cancers, and in the female reproductive tract. However, estrogens have important functions in almost every tissue in the body. Recent clinical trials such as the Women's Health Initiative have highlighted both the importance of estrogens and how little we know about the molecular mechanism of estrogens in these other tissues. In this review, we illustrate the diverse functions of estrogens in the bone, adipose tissue, skin, hair, brain, skeletal muscle and cardiovascular system, and how the loss of estrogens during aging affects these tissues. Early transcriptional targets of estrogen are reviewed in each tissue. We also describe the tissue-specific effects of selective estrogen receptor modulators (SERMs) used for the treatment of breast cancers and postmenopausal symptoms.

Biogerontology in Finland

This paper describes current biogerontology research in Finland especially in the universities with professorships in gerontology/geriatrics. If biogerontology is broadly taken to include all research in basic mechanisms of normal ageing as well as age-related diseases, the most prevalent current topics include basic research in genetics, mitochondrial function, musculoskeletal physiology, neurodegenerative and vascular diseases. The research activity of each institute and their international collaboration is briefly described with examples focused on recent publications in the field of biogerontology.