Characterization of heterokaryons between skeletal myoblasts and preadipocytes: myogenic potential of 3T3-L1 preadipocytes

Comparison of lipid deposition of intramuscular preadipocytes in Tan sheep co-cultured with satellite cells or alone

The purpose of this study was to investigate the effect of the skeletal muscle satellite cells (SMSCs) on the lipid deposition of the intramuscular preadipocytes (IMPs) in a co-culture system of the Tan sheep cells. The SMSCs and IMPs from Tan sheep were separated and cultured. After the two kinds of cells were separated and cultured, they were inoculated onto a transwell cell chamber co-culture plate for co-cultivation. When the cell density reached more than 90%, the cells were induced to differentiate. After the induction of the SMSCs differentiation for 8 days, the level of the IMPs differentiation and the expression levels of the differentiation marker genes and the key enzymes of the lipid metabolism were assessed. The results showed that the number and area of the lipid droplets in the IMPs in the co-culture system were significantly reduced compared to those in the IMPs culture alone (p < 0.05). Meanwhile, the expression levels of the PPARγ, c/EBPα, ACC, FAS mRNA in the IMPs were significantly decreased (p < 0.05); the expression level of aP2 mRNA was decreased, but the difference was not significant (p > 0.05).These findings indicate that the SMSCs of the Tan sheep in the co-culture system inhibited the lipid deposition by the IMPs.

Autologous myoblasts attenuate atrophy and improve tongue force in a denervated tongue model: a pilot study

OBJECTIVES/HYPOTHESIS

Autologous muscle-derived stem cell (MdSC) therapy is a promising treatment to restore function. No group has evaluated MdSC therapy in a denervated tongue model. The purpose of this pilot investigation was to determine the extent of autologous MdSC survival, effects on tongue muscle atrophy, maximal contractile force, and lingual pressure in a denervated ovine tongue model.

STUDY DESIGN

Pilot animal experiment.

METHODS

Bilateral implantable cuff electrodes were placed around the hypoglossal nerves in two Dorper cross ewes. Tensometer and high-resolution manometry (HRM) testing were performed during supermaximum hypoglossal nerve stimulation to assess baseline tongue strength. Sternocleidomastoid muscle biopsies were acquired to create autologous MdSC cultures. At 1 month, 5 × 10(8) green fluorescent protein (GFP)-labeled autologous MdSCs were injected into the partially denervated tongue. Two-months postinjection, lingual tensometer testing, HRM, and postmortem histological assessment were performed.

RESULTS

GFP+ myofibers were identified in denervated tongue specimens indicating MdSC survival. Muscle fiber diameter was larger in GFP+ fibers for both tongue specimens, suggesting attenuation of muscle atrophy. Myofiber diameter was larger in GFP+ myofibers than preinjury diameters, providing evidence of new muscle formation. These myogenic changes led to a 27% increase in maximal tongue contractile force and a 54% increase in maximum base of tongue pressure in one animal.

CONCLUSIONS

Autologous MdSC therapy may be a viable treatment for the partially denervated tongue, with current findings demonstrating that injected MdSCs survived and fused with tongue myofibers, with a resultant increase in myofiber diameter and an increase in tongue strength.

LEVEL OF EVIDENCE

N/A.

Response of the adipose tissue transcriptome to dihydrotestosterone in mice

Androgens have been postulated to be important modulators of adipose tissue metabolism and fat cell function. In the present study, we investigated the response of male and female mice retroperitoneal adipose tissue to the nonaromatizable androgen dihydrotestosterone (DHT). Adipose tissue samples were obtained in gonadectomized animals treated with vehicle (control group), or injected with 0.1 mg DHT 1, 3, 6, 12, 18, and 24 h prior to necropsy. Fourteen animals were pooled at each time point (total 196 animals). Transcripts that were significantly modulated were considered as androgen-responsive genes. Quantitative real-time RT-PCR was used to confirm results from the microarray analysis in a subset of 46 probe sets in male mice and 98 probe sets in female mice. Considering peak time vs. control, we confirmed 74.0 and 63.3% of the modulated genes by PCR in males and females, respectively. Four genes were significantly stimulated in a similar manner by DHT in both sexes, namely metallothionein 1, growth arrest and DNA-damage-inducible 45 gamma, cyclin-dependent kinase inhibitor 1A, and fk506-binding protein 5. All these genes appear to be involved in the regulation of adipocyte differentiation/proliferation and adipogenesis. In conclusion, this study, which evaluated the acute transcriptome response of adipose tissue to DHT in male and female mice, suggests that DHT consistently modulates genes involved in the regulation of adipogenesis in retroperitoneal adipose tissue of both male and female animals.

Both PPAR.GAMMA. and C/EBP.ALPHA. are Sufficient to Induce Transdifferentiation of Goat Fetal Myoblasts into Adipocytes

The present study was conducted to investigate whether goat fetal myoblasts with no inherent adipogenic potential can be induced to transdifferentiate into adipocytes. Goat fetal myoblasts were transiently transfected by the adipogenic transcription factors, peroxisome proliferator-activated receptor-gamma (PPARgamma) and CCAAT/enhancer-binding protein-alpha (C/EBPalpha). Both PPARgamma and C/EBPalpha were capable of inducing adipogenic transdifferentiation as indicated by the appearance of mature adipocytes when the transfected cells were cultured in adipogenic differentiation medium (ADM). Ectopic expression of PPARgamma induced endogenous C/EBPalpha expression and vice versa only when the cells were cultured in ADM. Removal of troglitazone, a PPARgamma agonist, from the ADM resulted in a dramatic decline in the number of adipocytes, indicating that PPARgamma stimulation is necessary to induce adipogenic transdifferentiation of goat fetal myoblasts. These results demonstrate for the first time that primary cultured myoblasts can be transdifferentiated into adipocytes.

Transcriptome of the subcutaneous adipose tissue in response to oral supplementation of type 2 Leprdb obese diabetic mice with niacin-bound chromium

The effects of oral niacin-bound chromium (NBC) supplementation on the subcutaneous fat tissue of type 2 Lepr db obese diabetic mice were examined using high-density comprehensive mouse genome (45,101 probe sets) expression arrays. The influence of such supplementation on the plasma cardiovascular risk factors of these mice was also investigated. Supplementation of NBC had no significant effect on age-dependent weight gain in the Lepr db obese diabetic mice. However, NBC lowered total cholesterol (TC), TC-to-HDL ratio, LDL cholesterol, and triglyceride levels while increasing HDL cholesterol in the blood plasma. No effect of NBC supplementation was observed on fasting blood glucose levels. Oral glucose tolerance test revealed a significantly improved clearance of blood glucose between 1 and 2 h of glucose challenge in NBC-supplemented mice. Unbiased genome-wide interrogation demonstrated that NBC resulted in the upregulation of muscle-specific gene expression in the fat tissue. Genes encoding proteins involved in glycolysis, muscle contraction, muscle metabolism, and muscle development were specifically upregulated in response to NBC supplementation. Genes in the adipose tissue that were downregulated in response to NBC supplementation included cell death-inducing DNA fragmentation factor (CIDEA) and uncoupling protein-1, which represent key components involved in the thermogenic role of brown adipose tissue and tocopherol transfer protein, the primary carrier of α-tocopherol to adipose tissue. The observation that CIDEA-null mice are resistant to obesity and diabetes suggests that the inhibitory role of NBC on CIDEA expression was favorable. Further studies testing the molecular basis of NBC function and long-term outcomes are warranted.

Comparison of viable cell yield from excised versus aspirated adipose tissue

The correction of soft-tissue defects by adipose tissue transplantation often produces poor and unpredictable results. The implantation of isolated and cultured preadipocytes offers a solution to this problem since these cells differentiate into adipocytes when implanted in vivo. A field of major interest is to maximize the yield of preadipocytes isolated from adipose tissue showing only low contamination with other cell types. Aspiration and excision are two concurrent clinical ways of harvesting adipose tissue for the isolation of preadipocytes. This tissue is usually discarded after surgery. In this study, the yield of preadipocytes obtained from liposuction material was compared to that of excised adipose tissue. Furthermore, we determined the loss of precursor cells if isolation of preadipocytes was delayed for 24 h. Preadipocytes were isolated from the stromal cell fraction of human subcutaneous adipose tissue samples. Harvesting of adipose tissue by suction was performed according to the Coleman procedure (manually applied negative pressure using a 10-ml syringe with a blunt tip cannula). Isolation was either carried out within 60 min after extraction or after storage for 24 h in culture medium at 4 degrees C. Isolated preadipocytes were cultured for 24 h, trypsinized and counted in a Neubauer chamber. Our results show clearly that the yield of preadipocytes isolated from liposuction material (within 60 min after extraction and after 24 h of storage) is higher than the cell yield from excised adipose tissue. Overnight storage for 24 h leads to a significant loss of preadipocytes in excised tissue but not in liposuction material. The high yield of cells isolated from liposuction material proves that extraction by suction does not damage the stromal cell fraction in the adipose tissue. If cell isolation is not performed immediately after the operation, liposuction material is clearly the better alternative for storage.

Formation and characterization of spontaneously formed heterokaryons between quail myoblasts and 3T3-L1 preadipocytes: correlation between differential plasticity and degree of differentiation

Skeletal muscle cells and adipose cells have a close relationship in developmental lineage. Our previous study has shown that the heterokaryons between quail myoblasts and undifferentiated 3T3-L1 cells (preadipocytes) normally differentiated into myotubes, whereas the heterokaryons between myoblasts and differentiated 3T3-L1 cells (adipocytes) failed myogenic differentiation. These results suggest differences between preadipocytes and adipocytes. The purpose of this study was to clarify whether preadipocytes have flexibility in differentiation before terminal adipose differentiation. Presumptive quail myoblasts transformed with a temperature-sensitive mutant of Rous sarcoma virus (QM-RSV cells) and mouse 3T3-L1 cells (either preadipocytes or adipocytes) were co-cultured for 48 h under conditions allowing myogenic differentiation. On co-culture between myoblasts and undifferentiated 3T3-L1 cells, heterokaryotic myotubes formed spontaneously, but not on co-culture with differentiated 3T3-L1 cells. In addition, the heterokaryotic myotubes expressed mouse myogenin derived from the 3T3-L1 cell gene. Our previous study indicated that the fusion sensitivity of differentiating myoblasts change with decreasing cholesterol of the cell membrane during myoblast fusion. Thus we compared the level of membrane cholesterol between undifferentiated and differentiated 3T3-L1 cells. The result showed that the level of membrane cholesterol in 3T3-L1 cells increases during adipose differentiation. Corresponding to the increase in membrane cholesterol content, differentiated 3T3-L1 cells had lower sensitivity to HVJ (Sendai virus)-mediated cell fusion than undifferentiated 3T3-L1 cells. This study demonstrated that 3T3-L1 cells at an undifferentiated state have a capacity for spontaneous fusion with differentiating myoblasts following myogenic differentiation, and that the capacity is lost after terminal adipose differentiation.