Date

2012

Author

Severcan, Feride
Puralı, Nuhan
Banerjee, Sreeparna

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Obesity, which arises from changes in lifestyle and feeding habits in developed and developing countries, is becoming a threat for human health due to its increasing prevelance. Especially, the increase in the consumption of high fat diets is one of the main factors that take role in the generation of obesity. Clinical disorders, such as type 2 diabetes, dislipidemia, cardiovascular diseases and hypertension, are all basic metabolic diseases in close relation with obesity. These metabolic disorders generally trigger each others’ prevalence. The common property shared by obesity and these metabolic disorders is the inability of insulin to exert its action on tissues, even though insulin is produced by the body. Impaired insulin sensitivity in skeletal muscle tissue is one of the most common symptom in pathophysiology of diabetes and obesity. While insulin resistance have not been yet fully established for clarity, in recent studies, more and more evidence reveals that the distribution and types of lipids are the deterministic factors in generation of insulin resistance. Therefore, determination of the distribution and types of lipids accumulated in the skeletal muscle are necessary in order to explain the generation of insulin resistance mechanism in obesity. The aim of this study was to establish the structural and functional changes in longissimus dorsi (LD) and quadriceps (Q) skeletal muscle tissue macromolecules, especially lipid, and determination of the types and distribution of the lipids within these tissues in control (C57BL/6J and DBA/2J), Berlin muscle mouse inbred (BMMI) lines and Berlin fat mouse inbred (BFMI) lines and thus, to do the characterization of these skeletal muscle tissues of inbred mouse models. For this this purpose, attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy was used to determine the properties of macromolecules, FTIR microspectroscopy was used to monitor the distribution of these macromolecules especially lipids within the skeletal muscles, confocal microscopy technique was used to monitor the lipid content of muscle fibers and to determine fibers types that these lipids accumulated more intensely and high performance liquid chromatography (HPLC) technique was used to determine the types and amounts of lipids stored in these muscles. In this study, skeletal muscle tissues of the control (C57BL/6J and DBA/2J), BMMI mice which were fed with standard breeding diet (SBD) and BFMI mice which were fed with either SBD or high-fat diet (HFD) were investigated. 14 In this study, serum levels of glucose, triglyceride and non-esterified fatty acid were found to be increased in BMMI806 among the BMMI lines and BFMI860, BFMI861 within the BFMI lines and these lines showed a slower response to insulin injection than the other lines. These results were the indicators of the development of insulin resistance in these lines. BMMI806, BFMI860 and BFMI861 lines represented different properties in comparison to the other lines. ATR-FTIR spectroscopic results revealed that BMMI806, BFMI860 ve BFMI861 mice possess higher amount of triglyceride, cholesterol ester and saturated lipid content, lower amount of unsaturated lipid content, more methly groups in lipid structure and lipids with shorther hydrocarbon chain lenght in comparison to other groups. The lipid content in skeletal muscles of all BFMI mice fed with a HFD increased, except for BFMI852 line which did not respond to feeding with HFD in terms of lipid content. The highest lipid content was found to be in BFMI860 line among the groups fed with a HFD. It had been demonstrated that the skeletal muscles of BMMI806 line amoung BMMI lines, BFMI860 and BFMI861 lines within BFMI mice had the lowest olefinic band area and unsaturation index; therefore these lines are more prone to lipid peroxidation. Lipids extracted from LD an Q skeletal muscles of control, BFMI and BMMI lines of SBD and also BFMI lines of HFD were separated, characterized and quantified by HPLC-ELSD technique. In BFMI lines, lipids were detected in higher concentrations regarding to BMMI lines. Among BFMI lines, the highest lipid concentrations were seen in BFMI860 and BFMI861 lines, respectively. In BFMI lines, other than BFMI860 and BFMI861, the concentration of detected lipids were low. The effects of HFD on the concentration of lipids were obvious. In BFMI lines which fed with HFD, had more lipid content compared to BFMI mice which fed with SBD. These findings support the ATRFTIR spectroscopic results, which was performed on the same tissues of same lines. In LD and Q muscles BMMI826 and BMMI866 lines, which were characterized as myostatin mutants, were found to have less lipid content. In myostatin wild-type BMMI806 line, the lipid concentration was detected to be higher than the other BMMI lines. These findings are also in agreement with the ATR-FTIR spectroscopic results. Lipid amounts in LD and Q skeletal muscles were also determined and compared with each other. According to the results, lipid concentration was found to be higher in LD skeletal muscle when compared to the lipid concentration in Q muscle. Via imaging techniques, higher amount of neutral lipid accumulation was observed in the cross-sections of skeletal muscle type IIa and intermediate muscle fiber, which do 15 have more oxidative metabolism. In these muscle fibers where high lipid accumulation is present, high lipit/protein distribution, high amount of methylene (CH2) groups, low amount of methyl groups (CH3) in the lipid structure, high amount of triglyceride content (carboynl, C=O) and lipids with longer chain lenght were observed. Furthermore, it was also found that, these fibers display a higher unsaturation index and lower glycogen content. This lipid accumulation was found to be the highest in the skeletal muscles of BFMI860 mice when compared to other obese mouse lines. The effect of HFD on BFMI860 mouse line regarding to the lipid accumulation, was observed to be more dramatic. When all results obtained were evaluated, with their genetically complex background, BFMI860 and BMMI806 were determined to be the most suitable lines for the investigation of spontaneous obesity in humans among all BFMI and BMMI lines. Furthermore, according to the results of this study, in LD muscles which is responsible for the posture and include more type IIa fibers than Q muscle, represented more significant results.

Subject Keywords

Obesity, Skeletal muscle, Insulin resistance, Mouse model, ATR-FTIR spektroscopy, FTIR microspektroscopy, Confocal microskopy, HPLC

URI

https://app.trdizin.gov.tr/publication/project/detail/TVRFMU5URXg
https://hdl.handle.net/11511/49917

Collections

Department of Biology, Project and Design