Helene Rundqvist

Endurance exercise activates matrix metalloproteinases in human skeletal muscle

In the present study, the effect of exercise training on the expression and activity of matrix metalloproteinases (MMPs) in the human skeletal muscle was investigated. Ten subjects exercised one leg for 45 min with restricted blood flow and then exercised the other leg at the same absolute workload with unrestricted blood flow. The exercises were conducted four times per week for 5 wk. Biopsies were taken from the vastus lateralis muscles of both legs at rest before the training period, after 10 days and 5 wk of training, and 2 h after the first exercise bout for analysis of MMP and tissue inhibitor of metalloproteinase-1 (TIMP-1) mRNA, enzyme activity, and protein expression. Levels of MMP-2, MMP-14, and TIMP-1 mRNA in muscle tissue increased after 10 days of training regardless of blood flow condition. MMP-2 mRNA level in laser-dissected myofibers and MMP-2 activity in whole muscle increased with training. The level of MMP-9 mRNA and activity increased after the first bout of exercise. Although MMP-9 mRNA levels appeared to be very low, the activity of MMP-9 after a single bout of exercise was similar to that of MMP-2 after 10 days of exercise. MMP-2 and MMP-9 protein was both present throughout the extracellular matrix of the muscle, both around fibers and capillaries, but MMP-2 was also present within the skeletal muscle fibers. These results show that MMPs are activated in skeletal muscle in nonpathological conditions such as voluntary exercise. The expression and time pattern indicate differences between the MMPs in regards of production sites as well as in the regulating mechanism.

An integrative analysis reveals coordinated reprogramming of the epigenome and the transcriptome in human skeletal muscle after training

Regular endurance exercise training induces beneficial functional and health effects in human skeletal muscle. The putative contribution to the training response of the epigenome as a mediator between genes and environment has not been clarified. Here we investigated the contribution of DNA methylation and associated transcriptomic changes in a well-controlled human intervention study. Training effects were mirrored by significant alterations in DNA methylation and gene expression in regions with a homogeneous muscle energetics and remodeling ontology. Moreover, a signature of DNA methylation and gene expression separated the samples based on training and gender. Differential DNA methylation was predominantly observed in enhancers, gene bodies and intergenic regions and less in CpG islands or promoters. We identified transcriptional regulator binding motifs of MRF, MEF2 and ETS proteins in the proximity of the changing sites. A transcriptional network analysis revealed modules harboring distinct ontologies and, interestingly, the overall direction of the changes of methylation within each module was inversely correlated to expression changes. In conclusion, we show that highly consistent and associated modifications in methylation and expression, concordant with observed health-enhancing phenotypic adaptations, are induced by a physiological stimulus.

Activation of the erythropoietin receptor in human skeletal muscle.

OBJECTIVE Erythropoietin receptor (EPOR) expression in non-hematological tissues has been shown to be activated by locally produced and/or systemically delivered EPO. Improved oxygen homeostasis, a well-established consequence of EPOR activation, is very important for human skeletal muscle performance. In the present study we investigate whether human skeletal muscle fibers and satellite cells express EPOR and if it is activated by exercise. DESIGN AND METHODS Ten healthy males performed 65 min of cycle exercise. Biopsies were obtained from the vastus lateralis muscle and femoral arterio-venous differences in EPO concentrations were estimated. RESULTS The EPOR protein was localized in areas corresponding to the sarcolemma and capillaries. Laser dissection identified EPOR mRNA expression in muscle fibers. Also, EPOR mRNA and protein were both detected in human skeletal muscle satellite cells. In the initial part of the exercise bout there was a release of EPO from the exercising leg to the circulation, possibly corresponding to an increased bioavailability of EPO. After exercise, EPOR mRNA and EPOR-associated JAK2 phosphorylation were increased. CONCLUSIONS Interaction with JAK2 is required for EPOR signaling and the increase found in phosphorylation is therefore closely linked to the activation of EPOR. The receptor activation by acute exercise suggests that signaling through EPOR is involved in exercise-induced skeletal muscle adaptation, thus extending the biological role of EPO into the skeletal muscle.

Effect of Acute Exercise on Prostate Cancer Cell Growth

Physical activity is associated with reduced risk of several cancers, including aggressive prostate cancer. The mechanisms mediating the effects are not yet understood; among the candidates are modifications of endogenous hormone levels. Long-term exercise is known to reduce serum levels of growth stimulating hormones. In contrast, the endocrine effects of acute endurance exercise include increased levels of mitogenic factors such as GH and IGF-1. It can be speculated that the elevation of serum growth factors may be detrimental to prostate cancer progression into malignancy. The incentive of the current study is to evaluate the effect of acute exercise serum on prostate cancer cell growth. We designed an exercise intervention where 10 male individuals performed 60 minutes of bicycle exercise at increasing intensity. Serum samples were obtained before (rest serum) and after completed exercise (exercise serum). The established prostate cancer cell line LNCaP was exposed to exercise or rest serum. Exercise serum from 9 out of 10 individuals had a growth inhibitory effect on LNCaP cells. Incubation with pooled exercise serum resulted in a 31% inhibition of LNCaP growth and pre-incubation before subcutaneous injection into SCID mice caused a delay in tumor formation. Serum analyses indicated two possible candidates for the effect; increased levels of IGFBP-1 and reduced levels of EGF. In conclusion, despite the fear of possible detrimental effects of acute exercise serum on tumor cell growth, we show that even the short-term effects seem to add to the overall beneficial influence of exercise on neoplasia.

Alternative splice variant PGC-1α-b is strongly induced by exercise in human skeletal muscle.

The present study investigated whether exercise induces the expression of PGC-1α splice variants in human skeletal muscle and the possible influence of metabolic perturbation on this response. The subjects exercised one leg for 45 min with restricted blood flow (R-leg), followed by 45 min of exercise using the other leg at the same absolute workload but with normal blood flow (NR-leg). This ischemic model (R-leg) has been shown previously to induce a greater metabolic perturbation and enhance the expression of PGC-1α beyond that observed in the NR-leg. Cultured human myotubes were used to test suggested exercise-induced regulatory stimuli of PGC-1α. We showed, for the first time, that transcripts from both the canonical promoter (PGC-1α-a) and the proposed upstream-located promoter (PGC-1α-b) are present in human skeletal muscle. Both transcripts were upregulated after exercise in the R-leg, but the fold change increase of PGC-1α-b was much greater than that of PGC-1α-a. No differences were observed between the two conditions regarding the marker for calcineurin activation, MCIP1, or p38 phosphorylation. AMPK phosphorylation increased to a greater extent in the R-leg, and AICAR stimulation of cultured human myotubes induced the expression of PGC-1α-a and PGC-1α-b. AICAR combined with norepinephrine yielded an additive effect on the PGC-1α-b expression only. Our results indicate clearly that exercise can activate an upstream promoter in humans and support AMPK as a major regulator of transcripts from the canonical PGC-1α promoter and the involvement of β-adrenergic stimulation in combination with AMPK in the regulation of PGC-1α-b.

Training response of mitochondrial transcription factors in human skeletal muscle

Aim:  Mitochondrial function is essential for physical performance and health. Aerobic fitness is positively associated with mitochondrial (mt) biogenesis in muscle cells through partly unknown regulatory mechanisms. The present study aimed to investigate the influence of exercise and training status on key mt transcription factors in relation to oxidative capacity in human skeletal muscle.

Tumour oxygenation: implications for breast cancer prognosis

There are areas of limited oxygen availability in most solid tumours, including breast cancer. Hypoxia in solid tumours is mainly a consequence of poor perfusion. Structural and functional abnormalities of newly formed tumour vessels cause spatial and temporal heterogeneity of tissue perfusion. The two principal mediators of hypoxia response, HIF‐1 and HIF‐2, are known to be stabilized at different oxygen levels and to have different temporal responses to hypoxia. Recently, stromal HIF‐1 and HIF‐2 have been suggested to have opposing roles in breast cancer progression. There is an established link between intralesional, severe hypoxia near areas of necrosis with high levels of HIF‐1 and poor prognosis in breast cancer. However, the biological effects of moderate hypoxia and the hypoxic response of stromal cells are currently topics of intense investigation.

Fibroblasts—a key host cell type in tumor initiation, progression, and metastasis

Abstract Tumor initiation, growth, invasion, and metastasis occur as a consequence of a complex interplay between the host environment and cancer cells. Fibroblasts are now recognized as a key host cell type involved in host–cancer signaling. This review discusses some recent studies that highlight the roles of fibroblasts in tumor initiation, early progression, invasion, and metastasis. Some clinical studies describing the prognostic significance of fibroblast-derived markers and signatures are also discussed.

Hypoxia and Metastasis in Breast Cancer

In this review we summarize the evidence for a role for hypoxic response in the biology of metastasis, with a particular emphasis on the metastasis of breast cancer and the function of the hypoxia inducible factor (HIF).

Role of Tumor Pericytes in the Recruitment of Myeloid-Derived Suppressor Cells

BACKGROUND Pericytes are members of the tumor stroma; however, little is known about their origin, function, or interaction with other tumor components. Emerging evidence suggest that pericytes may regulate leukocyte transmigration. Myeloid-derived suppressor cells (MDSC) are immature myeloid cells with powerful inhibitory effects on T-cell-mediated antitumor reactivity. METHODS We generated subcutaneous tumors in a genetic mouse model of pericyte deficiency (the pdgfb (ret/ret) mouse) and littermate control mice (n = 6-25). Gene expression profiles from 253 breast cancer patients (stage I-III) were evaluated for clinic-pathological parameters and survival using Cox proportional hazard ratios (HRs) and 95% confidence intervals (CIs) based on a two-sided Wald test. RESULTS We report that pericyte deficiency leads to increased transmigration of Gr1(+)/CD11b(+) cells in experimentally induced tumors. Pericyte deficiency produced defective tumor vasculature, resulting in a more hypoxic microenvironment promoting IL-6 upregulation in the malignant cells. Silencing IL-6 expression in tumor cells attenuated the observed differences in MDSC transmigration. Restoring the pericyte coverage in tumors abrogated the increased MDSC trafficking to pericyte-deficient tumors. MDSC accumulation in tumors led to increases in tumor growth and in circulating malignant cells. Finally, gene expression analysis from human breast cancer patients revealed increased expression of the human MDSC markers CD33 and S100A9 with concomitant decreased expression of pericyte genes and was associated with poor prognosis (HR = 1.88, 95% CI = 1.08 to 3.25, P = .03). CONCLUSIONS Our data uncovers a novel paracrine interaction between tumor pericytes and inflammatory cells and delineates the cellular events resulting in the recruitment of MDSC to tumors. Furthermore, we propose for the first time a role for tumor pericytes in modulating the expression of immune mediators in malignant cells by promoting a hypoxic microenvironment.