TY  - JOUR
AB  - Skeletal muscle mediates the beneficial effects of exercise, thereby improving insulin sensitivity and reducing the risk for type 2 diabetes. Current human skeletal muscle models in vitro are incapable of fully recapitulating its physiological functions especially muscle contractility. By supplementation of insulin-like growth factor 1 (IGF1), a growth factor secreted by myofibers in vivo, we aimed to overcome these limitations. We monitored the differentiation process starting from primary human CD56-positive myoblasts in the presence/absence of IGF1 in serum-free medium in daily collected samples for 10 days. IGF1-supported differentiation formed thicker multinucleated myotubes showing physiological contraction upon electrical pulse stimulation following day 6. Myotubes without IGF1 were almost incapable of contraction. IGF1-treatment shifted the proteome toward skeletal muscle-specific proteins that contribute to myofibril and sarcomere assembly, striated muscle contraction, and ATP production. Elevated PPARGC1A, MYH7 and reduced MYH1/2 suggest a more oxidative phenotype further demonstrated by higher abundance of proteins of the respiratory chain and elevated mitochondrial respiration. IGF1-treatment also upregulated GLUT4 and increased insulin-dependent glucose uptake compared to myotubes differentiated without IGF1. To conclude, addition of IGF1 to serum-free medium significantly improves the differentiation of human myotubes that showed enhanced myofibril formation, response to electrical pulse stimulation, oxidative respiratory capacity and glucose metabolism overcoming limitations of previous standards. This novel protocol enables investigation of muscular exercise on a molecular level.
AU  - Dreher, S.I.*
AU  - Grubba, P.*
AU  - von Toerne, C.
AU  - Moruzzi, A.*
AU  - Maurer, J.*
AU  - Goj, T.*
AU  - Birkenfeld, A.L.
AU  - Peter, A.
AU  - Loskill, P.*
AU  - Hauck, S.M.
AU  - Weigert, C.
C1  - 70630
C2  - 55782
CY  - 6120 Executive Blvd, Suite 600, Rockville, Md, United States
SP  - C1462-C1481
TI  - IGF1 promotes human myotube differentiation toward a mature metabolic and contractile phenotype.
JO  - Am. J. Physiol.-Cell Physiol.
VL  - 326
IS  - 5
PB  - Amer Physiological Soc
PY  - 2024
SN  - 0363-6143
ER  - 

TY  - JOUR
AB  - Fascia is a specialized connective tissue system that permiate, encapsulate, and interconnect between tissues and organs throughout the body. The fascia system regulates pain sensation, organ inflammation, trauma, and a fibrotic diseases. This mini-review summarizes recent findings from animal models, which reveal the inter-dependency between tissues/organs and the fascia system. special mechanisms of fascia response to skin inflammatory and fibrotic microenvironment via the dynamics within the fascia in trauma models, the functional heterogeneity of its fascia-born fibroblasts, and cellular communication, to highlight the significance of their stage-specific differentiation to disease progression. Understanding the molecular mechanisms and cellular processes within the fascia microenvironment, may serve as basis for future clinical translation.
AU  - Lin, Y.
AU  - Dai, R.
AU  - Vogelaar, G.
AU  - Rinkevich, Y.
C1  - 70902
C2  - 55895
CY  - 6120 Executive Blvd, Suite 600, Rockville, Md, United States
SP  - C357-C361
TI  - Mini-review: Organ dependency on fascia connective tissue.
JO  - Am. J. Physiol.-Cell Physiol.
VL  - 327
IS  - 2
PB  - Amer Physiological Soc
PY  - 2024
SN  - 0363-6143
ER  - 

TY  - JOUR
AB  - Metformin-induced glycolysis and lactate production can lead to acidosis as a life-threatening side effect, but slight increases in blood lactate levels in a physiological range were also reported in metformin-treated patients. However, how metformin increases systemic lactate concentrations is only partly understood. Because human skeletal muscle has a high capacity to produce lactate, the aim was to elucidate the dose-dependent regulation of metformin-induced lactate production and the potential contribution of skeletal muscle to blood lactate levels under metformin treatment. This was examined by using metformin treatment (16-776 μM) of primary human myotubes and by 17 days of metformin treatment in humans. As from 78 µM, metformin induced lactate production and secretion and glucose consumption. Investigating the cellular redox state by mitochondrial respirometry, we found metformin to inhibit the respiratory chain complex I (776 µM, P < 0.01) along with decreasing the [NAD+]:[NADH] ratio (776 µM, P < 0.001). RNA sequencing and phospho-immunoblot data indicate inhibition of pyruvate oxidation mediated through phosphorylation of the pyruvate dehydrogenase (PDH) complex (39 µM, P < 0.01). On the other hand, in human skeletal muscle, phosphorylation of PDH was not altered by metformin. Nonetheless, blood lactate levels were increased under metformin treatment (P < 0.05). In conclusion, the findings suggest that metformin-induced inhibition of pyruvate oxidation combined with altered cellular redox state shifts the equilibrium of the lactate dehydrogenase (LDH) reaction leading to a dose-dependent lactate production in primary human myotubes.NEW & NOTEWORTHY Metformin shifts the equilibrium of lactate dehydrogenase (LDH) reaction by low dose-induced phosphorylation of pyruvate dehydrogenase (PDH) resulting in inhibition of pyruvate oxidation and high dose-induced increase in NADH, which explains the dose-dependent lactate production of differentiated human skeletal muscle cells.
AU  - Maurer, J.*
AU  - Zhao, X.*
AU  - Irmler, M.
AU  - Gudiksen, A.*
AU  - Pilmark, N.S.*
AU  - Li, Q.*
AU  - Goj, T.*
AU  - Beckers, J.
AU  - Hrabě de Angelis, M.
AU  - Birkenfeld, A.L.
AU  - Peter, A.
AU  - Lehmann, R.
AU  - Pilegaard, H.*
AU  - Karstoft, K.*
AU  - Xu, G.*
AU  - Weigert, C.
C1  - 68609
C2  - 54712
CY  - 6120 Executive Blvd, Suite 600, Rockville, Md, United States
SP  - C1131-C1143
TI  - Redox state and altered pyruvate metabolism contribute to a dose-dependent metformin-induced lactate production of human myotubes.
JO  - Am. J. Physiol.-Cell Physiol.
VL  - 325
IS  - 4
PB  - Amer Physiological Soc
PY  - 2023
SN  - 0363-6143
ER  - 

TY  - JOUR
AB  - Obesity, especially visceral fat accumulation, increases the risk of type 2 diabetes (T2D). The purpose of this study was to investigate the impact of T2D on the pancreatic fat depot. Pancreatic fat pads from 17 partial pancreatectomized patients (PPP) were collected, pancreatic preadipocytes isolated and in vitro differentiated. Patients were grouped using HbA1c into normal glucose tolerant (NGT), prediabetic (PD) and T2D. Transcriptome profiles of preadipocytes and adipocytes were assessed by RNAseq. Insulin sensitivity was estimated by quantifying AKT phosphorylation on western blots. Lipogenic capacity was assessed with oil red O staining, lipolytic activity via fatty acid release. Secreted factors were measured using ELISA. Comparative transcriptome analysis of preadipocytes and adipocytes indicates defective upregulation of genes governing adipogenesis (NR1H3), lipogenesis (FASN, SCD, ELOVL6, FADS1) and lipolysis (LIPE) during differentiation of cells from T2D-PPP. In addition, the ratio of leptin/adiponectin mRNA was higher in T2D than in NGT-PPP. Preadipocytes and adipocytes of NGT-PPP were more insulin sensitive than T2D-PPP cells in regard to AKT phosphorylation. Triglyceride accumulation was similar in NGT and T2D adipocytes. Despite a high expression of the receptors NPR1 and NPR2 in NGT and T2D adipocytes, lipolysis was stimulated by ANP 1.74-fold in NGT cells only. This stimulation was further increased by the PDE5 inhibitor dipyridamole (3.09-fold). Dipyridamole and forskolin increased lipolysis receptor-independently 1.88-fold and 1.48-fold, respectively, solely in NGT cells. In conclusion, the metabolic status persistently affects differentiation and lipolysis of pancreatic adipocytes. These alterations could aggravate the development of T2D.
AU  - Barroso Oquendo, M.*
AU  - Siegel-Axel, D.I.*
AU  - Gerst, F.
AU  - Lorza-Gil, E.
AU  - Moller, A.
AU  - Wagner, R.
AU  - Machann, J.
AU  - Fend, F.*
AU  - Königsrainer, A.*
AU  - Heni, M.
AU  - Häring, H.-U.
AU  - Ullrich, S.
AU  - Birkenfeld, A.L.
C1  - 61756
C2  - 50291
CY  - 9650 Rockville Pike, Bethesda, Md 20814 Usa
SP  - C1000-C1012
TI  - Pancreatic fat cells of humans with type 2 diabetes display reduced adipogenic and lipolytic activity.
JO  - Am. J. Physiol.-Cell Physiol.
VL  - 320
IS  - 6
PB  - Amer Physiological Soc
PY  - 2021
SN  - 0363-6143
ER  - 

TY  - JOUR
AB  - Hoene M, Runge H, Haring HU, Schleicher ED, Weigert C. Interleukin-6 promotes myogenic differentiation of mouse skeletal muscle cells: role of the STAT3 pathway. Am J Physiol Cell Physiol 304: C128-C136, 2013. First published October 31, 2012; doi:10.1152/ajpcell.00025.2012.-Myogenic differentiation of skeletal muscle cells is characterized by a sequence of events that include activation of signal transducer and activator of transcription 3 (STAT3) and enhanced expression of its target gene Socs3. Autocrine effects of IL-6 may contribute to the activation of the STAT3-Socs3 cascade and thus to myogenic differentiation. The importance of IL-6 and STAT3 for the differentiation process was studied in C2C12 cells and in primary mouse wild-type and IL-6(-/-) skeletal muscle cells. In differentiating C2C12 myoblasts, the upregulation of IL-6 mRNA expression and protein secretion started after increased phosphorylation of STAT3 on tyrosine 705 and increased mRNA expression of Socs3 was observed. Knockdown of STAT3 and IL-6 mRNA in differentiating C2C12 myoblasts impaired the expression of the myogenic markers myogenin and MyHC IIb and subsequently myotube fusion. However, the knockdown of IL-6 did not prevent the induction of STAT3 tyrosine phosphorylation. The IL-6-independent activation of STAT3 was verified in differentiating primary IL-6(-/-) myoblasts. The phosphorylation of STAT3 and the expression levels of STAT3, Socs3, and myogenin during differentiation were comparable in the primary myoblasts independent of the genotype. However, IL-6(-/-) cells failed to induce MyHC IIb expression to the same level as in wild-type cells and showed reduced myotube formation. Supplementation of IL-6 could partially restore the fusion of IL-6(-/-) cells. These data demonstrate that IL-6 depletion during myogenic differentiation does not reduce the activation of the STAT3-Socs3 cascade, while IL-6 and STAT3 are both necessary to promote myotube fusion.
AU  - Hoene, M.
AU  - Runge, H.*
AU  - Häring, H.-U.
AU  - Schleicher, E.D.
AU  - Weigert, C.
C1  - 22659
C2  - 30929
SP  - 128-136
TI  - Interleukin-6 promotes myogenic differentiation of mouse skeletal muscle cells: Role of the STAT3 pathway.
JO  - Am. J. Physiol.-Cell Physiol.
VL  - 304
IS  - 2
PB  - American Physiological Society
PY  - 2013
SN  - 0363-6143
ER  - 

TY  - JOUR
AB  - Muscle contraction during exercise is a major stimulus for the release of peptides and proteins (myokines) that are supposed to take part in the beneficial adaptation to exercise. We hypothesize that application of an in vitro exercise stimulus as electric pulse stimulation (EPS) to human myotubes enables the investigation of the molecular response to exercise in a clearly defined model. We applied EPS for 24 h to primary human myotubes and studied the whole genome-wide transcriptional response as well as the release of candidate myokines. We observed 183 differentially regulated transcripts with fold changes >1.3. The transcriptional response resembles several properties of the in vivo situation in the skeletal muscle after endurance exercise, namely significant enrichment of pathways associated with interleukin and chemokine signaling, lipid metabolism, and antioxidant defense. Multiplex immunoassays verified the translation of the transcriptional response of several cytokines into high-secretion levels (IL-6, IL-8, CXCL1, LIF, CSF3, IL-1B, and TNF) and the increased secretion of further myokines such as angiopoietin-like 4. Notably, EPS did not induce the release of creatine kinase. Inhibitor studies and immunoblotting revealed the participation of ERK1/2-, JNK-, and NF-κB-dependent pathways in the upregulation of myokines. To conclude, our data highlight the importance of skeletal muscle cells as endocrine cells. This in vitro exercise model is not only suitable to identify exercise-regulated myokines, but it might be applied to primary human myotubes obtained from different muscle biopsy donors to study the molecular mechanisms of the individual response to exercise.
AU  - Scheler, M.
AU  - Irmler, M.
AU  - Lerch, S.
AU  - Hartwig, S.
AU  - Staiger, H.
AU  - Al-Hasani, H.
AU  - Beckers, J.
AU  - Hrabě de Angelis, M.
AU  - Häring, H.-U.
AU  - Weigert, C.
C1  - 28037
C2  - 32914
SP  - C877-C886
TI  - Cytokine response of primary human myotubes in an in vitro exercise model.
JO  - Am. J. Physiol.-Cell Physiol.
VL  - 305
IS  - 8
PB  - Amer. Physiological Soc.
PY  - 2013
SN  - 0363-6143
ER  -