Fred Haugen

Inhibition by insulin of resistin gene expression in 3T3-L1 adipocytes.

Expression of the gene encoding resistin, a low molecular weight protein secreted from adipose tissue postulated to link obesity and type II diabetes, was examined in 3T3‐L1 adipocytes. Resistin mRNA was detected in 3T3‐L1 cells by day 3 following induction of differentiation into adipocytes; by day 4 the level of resistin mRNA peaked and remained high. The PPARγ activators, rosiglitazone or darglitazone, reduced the level of resistin mRNA. Dexamethasone upregulated resistin mRNA level, but no effect was observed with the β3‐adrenoceptor agonist, BRL 37344. A substantial reduction in resistin mRNA level was observed with insulin, which induced decreases at physiological concentrations. Insulin may be a major inhibitor of resistin production, and this does not support a role for resistin in insulin resistance.

Adiponectin is reduced in gestational diabetes mellitus in normal weight women

Background.  Adiponectin is an adipose tissue‐derived protein counteracting insulin resistance and inflammation. We have compared women with gestational diabetes mellitus (GDM; n = 22) and normal pregnancies (controls; n = 29) to evaluate whether adiponectin represents a link between endocrine function of adipose tissue and the development of diabetes during pregnancy.

IL-7 is expressed and secreted by human skeletal muscle cells

In addition to generating movement, skeletal muscle may have a function as a secretory organ. The aim of the present study was to identify novel proteins with signaling capabilities secreted from skeletal muscle cells. IL-7 was detected in media conditioned by primary cultures of human myotubes differentiated from satellite cells, and concentrations increased with incubation time. By immunoblotting and real-time RT-PCR IL-7 expression was confirmed at both protein and mRNA levels. Furthermore, with immunofluorescence and specific antisera, multinucleated myotubes were found to coexpress IL-7 and myosin heavy chain. During differentiation of human myotubes from satellite cells, IL-7 expression increased at mRNA and protein levels. In contrast, mRNA expression of the IL-7 receptor was 80% lower in myotubes compared with satellite cells. Incubations with recombinant IL-7 under differentiation conditions caused approximately 35% reduction in mRNA for the terminal myogenic markers myosin heavy chain 2 (MYH2) and myogenin (MYOG), suggesting that IL-7 may act on satellite cells to inhibit development of the muscle fiber phenotype. Alternative routes of cell development were investigated, and IL-7 increased migration of satellite cells by 40% after 48 h in a Transwell system, whereas cell proliferation remained unchanged. In vivo, real-time RT-PCR analysis of musculus vastus lateralis (n = 10) and musculus trapezius (n = 7) biopsies taken from male individuals undergoing a strength training program demonstrated that after 11 wk mean IL-7 mRNA increased by threefold (P = 0.01) and fourfold (P = 0.04), respectively. In conclusion, we have demonstrated that IL-7 is a novel myokine regulated both in vitro and in vivo, and it may play a role in the regulation of muscle cell development.

Proteomic identification of secreted proteins from human skeletal muscle cells and expression in response to strength training

Regular physical activity protects against several types of diseases. This may involve altered secretion of signaling proteins from skeletal muscle. Our aim was to identify the most abundantly secreted proteins in cultures of human skeletal muscle cells and to monitor their expression in muscles of strength-training individuals. A total of 236 proteins were detected by proteome analysis in medium conditioned by cultured human myotubes, which was narrowed down to identification of 18 classically secreted proteins expressed in skeletal muscle, using the SignalP 3.0 and Human Genome Expression Profile databases together with a published mRNA-based reconstruction of the human skeletal muscle secretome. For 17 of the secreted proteins, expression was confirmed at the mRNA level in cultured human myotubes as well as in biopsies of human skeletal muscles. RT-PCR analyses showed that 15 of the secreted muscle proteins had significantly enhanced mRNA expression in m. vastus lateralis and/or m. trapezius after 11 wk of strength training among healthy volunteers. For example, secreted protein acidic and rich in cysteine, a secretory protein in the membrane fraction of skeletal muscle fibers, was increased 3- and 10-fold in m. vastus lateralis and m. trapezius, respectively. Identification of proteins secreted by skeletal muscle cells in vitro facilitated the discovery of novel responses in skeletal muscles of strength-training individuals.

Increased circulating mitochondrial DNA after myocardial infarction

DBP (R=0.022; p=0.01), LVM index (R=0.124 pb0.001) and body surface area (R=0.068; pb0.001) associated with AoRD in a model adjusted for age, gender, diabetes mellitus, hypertension, brachial supine SBP and triglycerides. This report provided novel knowledge that either in subjects with low cardiovascular risk (sample A) or in individuals with cardiovascular risk factors (sample B), leg BP, but not brachial BP, was independently related to AoRD. Moreover, the present results showed that changes in body posture influenced this relationship. These findings might have clinical implications. First, they could provide a novel indication for lower limbBPmeasurementas a predictor of AoRD,whichmightexpand its use in clinical practice. Currently, leg BP evaluation is not routinely performed, except when there is suspicion of aortic constriction or peripheral artery insufficiency [9,10]. Second, they suggest that evaluation of leg BP in orthostatic posture might be useful, at least in subjects with cardiovascular risk factors. To our knowledge, there are no reference values for leg BP measured in standing position and no previous study evaluated the relationship between orthostatic leg BP and vascular phenotypes. Conversely, current guidelines recommend assessmentof legBPonly inhorizontal position [9]. Therefore our results may shed novel light in a neglected BP measurement. In conclusion, our study demonstrated that leg BP was associated with AoRD in individuals with or without cardiovascular risk factors, and further showed that changes in body posture played a role in this relationship. Despite the underlying mechanisms, these findings suggest that leg BP evaluation might be an alternative approach in order to predict AoRD. However, further studies in other populations are necessary to confirm this assumption.

Diet-induced obesity increases NF-κB signaling in reporter mice

The nuclear factor (NF)-κB is a primary regulator of inflammatory responses and may be linked to pathology associated with obesity. We investigated the progression of NF-κB activity during a 12-week feeding period on a high-fat diet (HFD) or a low-fat diet (LFD) using NF-κB luciferase reporter mice. In vivo imaging of luciferase activity showed that NF-κB activity was higher in the HFD mice compared with LFD-fed mice. Thorax region of HFD females displayed fourfold higher activity compared with LFD females, while no such increase was evident in males. In male HFD mice, abdominal NF-κB activity was increased twofold compared with the LFD males, while females had unchanged NF-κB activity in the abdomen by HFD. HFD males, but not females, exhibited evident glucose intolerance during the study. In conclusion, HFD increased NF-κB activity in both female and male mice. However, HFD differentially increased activity in males and females. The moderate increase in abdomen of male mice may be linked to glucose intolerance.

Expression of perilipins in human skeletal muscle in vitro and in vivo in relation to diet, exercise and energy balance.

The perilipin proteins enclose intracellular lipid droplets. We describe the mRNA expression of the five perilipins in human skeletal muscle in relation to fatty acid supply, exercise and energy balance. We observed that all perilipins were expressed in skeletal muscle biopsies with the highest mRNA levels of perilipin 2, 4 and 5. Cultured myotubes predominantly expressed perilipin 2 and 3. In vitro, incubation of myotubes with fatty acids enhanced mRNA expression of perilipin 1, 2 and 4. In vivo, low fat diet increased mRNA levels of perilipin 3 and 4. Endurance training, but not strength training, enhanced the expression of perilipin 2 and 3. Perilipin 1 mRNA correlated positively with body fat mass, whereas none of the perilipins were associated with insulin sensitivity. In conclusion, all perilipins mRNAs were expressed in human skeletal muscle. Diet as well as endurance exercise modulated the expression of perilipins.

Retinoic acid signalling is activated in the postischemic heart and may influence remodelling

Background All-trans retinoic acid (atRA), an active derivative of vitamin A, regulates cell differentiation, proliferation and cardiac morphogenesis via transcriptional activation of retinoic acid receptors (RARs) acting on retinoic acid response elements (RARE).We hypothesized that the retinoic acid (RA) signalling pathway is activated in myocardial ischemia and postischemic remodelling. Methods and Findings Myocardial infarction was induced through ligating the left coronary artery in mice. In vivo cardiac activation of the RARs was measured by imaging RARE-luciferase reporter mice, and analysing expression of RAR target genes and proteins by real time RT-PCR and western blot. Endogenous retinoids in postinfarcted hearts were analysed by triple-stage liquid chromatography/tandem mass spectrometry. Cardiomyocytes (CM) and cardiofibroblasts (CF) were isolated from infarcted and sham operated RARE luciferase reporter hearts and monitored for RAR activity and expression of target genes. The effect of atRA on CF proliferation was evaluated by EdU incorporation. Myocardial infarction increased thoracic RAR activity in vivo (p<0.001), which was ascribed to the heart through ex vivo imaging (p = 0.002) with the largest signal 1 week postinfarct. This was accompanied by increased cardiac gene and protein expression of the RAR target genes retinol binding protein 1 (p = 0.01 for RNA, p = 0,006 for protein) and aldehyde dehydrogenase 1A2 (p = 0.04 for RNA, p = 0,014 for protein), while gene expression of cytochrome P450 26B1 was downregulated (p = 0.007). Concomitantly, retinol accumulated in the infarcted zone (p = 0.02). CM and CF isolated from infarcted hearts had higher luminescence than those from sham operated hearts (p = 0.02 and p = 0.008). AtRA inhibited CF proliferation in vitro (p = 0.02). Conclusion The RA signalling pathway is activated in postischemic hearts and may play a role in regulation of damage and repair during remodelling.

Expression of bone morphogenetic protein 4 and its receptors in the remodeling heart.

AIMS Heart failure is associated with activation of fetal gene programs. Bone morphogenetic proteins (BMPs) regulate embryonic development through interaction with BMP receptors (BMPRs) on the cell surface. We investigated if the expression of BMP4 and its receptors BMPR1a and BMPR2 were activated in post-infarction remodeling and heart failure. MAIN METHODS Left ventricular biopsies were taken from explanted hearts of patients with end-stage heart failure due to dilated cardiomyopathy (CMP; n=15) or ischemic heart disease (CAD; n=9), and compared with homograft control preparations from organ donors deceased due to non-cardiac causes (n=7). Other samples were taken from patients undergoing coronary artery bypass grafting (CABG; n=11). Mice were subjected to induced infarction by permanent coronary artery ligation or sham operation, and hearts were sampled serially thereafter (n=7 at each time point). KEY FINDINGS Human and mouse hearts expressed BMP4 and both receptor subtypes. CABG and CMP patients had increased expression of mRNA encoding for BMP4, but unchanged protein. Mouse hearts had increased BMP4 precursor protein 24h after infarction. BMPR1a protein decreased in CAD patients and initially in postinfarcted mouse hearts, but increased again in the latter after two weeks. Human recombinant BMP4 promoted survival after H2O2 injury in HL-1 cells, and also protected adult mouse cardiomyocytes against hypoxia-reoxygenation injury. SIGNIFICANCE Adult hearts express BMP4, the mRNA increasingly so in patients with coronary artery disease with good cardiac function. BMPRs are downregulated in cardiac remodeling and failure. Recombinant BMP4 has protective effects on cultured cardiomyocytes.

Protecting the heart through delivering DNA encoding for heme oxygenase-1 into skeletal muscle

AIM To evaluate if remote gene delivery of HMOX-1 prior to myocardial infarction can prevent cardiac remodeling and preserve function, without causing general angiogenesis. MAIN METHODS Right quadriceps muscles of mice were treated with DNA encoding for HMOX-1 or empty vector (pcDNA) and electroporated to enhance nuclear uptake, while a third group received saline. Transfection efficacy was evaluated by real time PCR and situ hybridization in transfected muscle, contralateral muscle, and heart. Seven days after transfection baseline echocardiography was performed. Myocardial infarction was induced by ligation of the left coronary artery. Six weeks later heart function was reassessed by echocardiography. Hearts were extracted for evaluation of infarct size. Immunoflorescent staining was used to evaluate angiogenesis using the endothelial marker CD31 in cross-sections of the transfected quadriceps muscle, the untreated muscle, and hearts. KEY FINDINGS Gene delivery of HMOX-1 leads to a local expression of HMOX-1 in the treated muscle, but not in any other organ. HMOX-1 treated mice had reduced infarct size (p=0.03) and improved function evident as higher ejection fraction (p=0.001), improved fractional shortening (p<0.0001) and higher stroke volume (p=0.002). HMOX-1 did not cause angiogenesis in the heart or skeletal muscle. SIGNIFICANCE Remote delivery of DNA encoding for HMOX-1 was cardioprotective, as evidenced by preserved cardiac structure and function. Angiogenesis was not induced by HMOX-1 treatment.