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

Research progress of intramuscular fat formation based on co-culture

Intramuscular fat (IMF) is closely related to the meat quality of livestock and poultry. As a new cell culture technique in vitro, cell co-culture has been gradually applied to the related research of IMF formation because it can simulate the changes of microenvironment in vivo during the process of IMF cell formation. In the co-culture model, in addition to studying the effects of skeletal muscle cells on the proliferation and differentiation of IMF, we can also consider the role of many secretion factors in the formation of IMF, thus making the cell research in vitro closer to the real level in vivo. This paper reviewed the generation and origin of IMF, summarized the existing co-culture methods and systems, and discussed the advantages and disadvantages of each method as well as the challenges faced in the establishment of the system, with emphasis on the current status of research on the formation of IMF for human and animal based on co-culture technology.

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.

Adipocytes suppress differentiation of muscle cells in a co-culture system

The development of adipose tissue in skeletal muscle is important for improving meat quality. However, it is still unclear how adipocytes grow in the proximity of muscle fibers. We hypothesized that adipocytes would suppress muscle cell growth so as to grow dominantly within muscle. In this study, we investigated the effect of adipocytes on the differentiation of muscle cells in a co-culture system. The fusion index of C2C12 myoblasts co-cultured with 3T3-L1 adipocytes was significantly lower than that of the control. The expression of myogenin and myosin heavy chain in C2C12 muscle cells co-cultured with 3T3-L1 adipocytes was significantly lower than in the control. Furthermore, the expression of Atrogin-1 and MuRF-1 was higher in C2C12 muscle cells co-cultured with 3T3-L1 adipocytes than the control. These results suggest that 3T3-L1 adipocytes suppress the differentiation of C2C12 myoblasts. In addition, 3T3-L1 adipocytes induced the expression and secretion of IL-6 in C2C12 muscle cells. The fusion index and myotube diameter were higher in C2C12 muscle cells co-cultured with 3T3-L1 cells in medium containing IL-6-neutralizing antibody than the control. Taken together, there is a possibility that adipocyte-induced IL-6 expression in muscle cells could be involved in the inhibition of muscle cell differentiation via autocrine.

The proliferation and differentiation characteristics of co-cultured porcine preadipocytes and muscle satellite cells in vitro

To explore the proliferation and differentiation characteristics of co-cultured porcine preadipocytes and muscle satellite cells, preadipocytes and muscle satellite cells were isolated from the healthy nascent landrace. Oil Red O stain and desmin immunohistochemistry were used to identify the two solo-cultured cells. Methyl thiazolyl tetrazolium (MTT) colorimetric assay was used to detect the proliferation characteristic of co-cultured cells, and the expression level of differentiation marker genes lipoprotein lipase (LPL), peroxisome proliferator-activated receptors (PPARγ), myogenic factor 5 (Myf5), myogenin (MyoG) were analyzed with reverse transcription PCR (RT-PCR) and western blot. The success of co-culture system was proved. In the co-cultured cells, slight lipid droplets were observed and appeared more slowly. The polykaryocytes fused into myotubes in co-cultured cells were less and relatively slow than that in solo myocytes. After fusion, the proliferation rate of co-cultured cells was higher than that in the solo-cultured muscle satellite cells (P < 0.01), and the duration were also longer. On day 5 and 10, the expression of the marker genes in earlier stage of cell differentiation (LPL and Myf5) were lower than those in the solo-cultured cells (P < 0.01) (except LPL gene at day 5). Moreover, the expression of intermediate and advanced stages' maker genes (PPARγ2 and MyoG) were hardly detectable at day 5, but increased significantly on day 10 (P < 0.01). These results confirm that the co-culture system could facilitate the cells' growth and proliferation, meanwhile, inhibited the cell differentiation.