Intramyocellular lipid (IMCL) accumulation has been linked to both insulin-resistant and insulin-sensitive (athletes) states. Biochemical analysis of intramuscular triglyceride composition is confounded by extramyocellular triglycerides in biopsy samples, and hence the specific composition of IMCLs is unknown in these states. 1 H magnetic resonance spectroscopy (MRS) can be used to overcome this problem. Thus, we used a recently validated 1 H MRS method to compare the compositional saturation index (CH 2 :CH 3 ) and concentration independent of the composition (CH 3 ) of IMCLs in the soleus and tibialis anterior muscles of 16 female insulin-resistant lipodystrophic subjects with that of age- and gender-matched athletes ( n = 14) and healthy controls ( n = 41). The IMCL CH 2 :CH 3 ratio was significantly higher in both muscles of the lipodystrophic subjects compared with controls but was similar in athletes and controls. IMCL CH 2 :CH 3 was dependent on the IMCL concentration in the controls and, after adjusting the compositional index for quantity (CH 2 :CH 3adj ), could distinguish lipodystrophics from athletes. This CH 2 :CH 3adj marker had a stronger relationship with insulin resistance than IMCL concentration alone and was inversely related to VO 2max . The association of insulin resistance with the accumulation of saturated IMCLs is consistent with a potential pathogenic role for saturated fat and the reported benefits of exercise and diet in insulin-resistant states.
The use of stem/progenitor cells represents a promising approach to treat craniofacial bone defects, but successful treatments will rely on the availability of cells that can be expanded in vitroand which will differentiate appropriately in vivo. The calvaria may represent a source of autologous cells for such purposes. We demonstrate expression of stem cell antigen-1 (Sca-1) in mouse calvaria. We isolated Sca-1+ and Sca-1– cells at high purity and tested the ability of these cells to differentiate into adipose and bone. We show that the Sca-1+ cell fraction has adipogenic differentiation potential and that the cell Sca-1– fraction has osteogenic differentiation potential. The Sca-1+ cell fraction partially retains its adipogenic differentiation potential and the Sca-1– cell fraction partially retains its osteogenic differentiation potential after in vitroexpansion. These data suggest that the calvaria may be used as a source of stem/progenitor cells that can be expanded in vitroand transplanted in vivofor craniofacial tissue regeneration.
1 Context: Paradoxically, intramyocellular lipid (IMCL) accumulation has been linked to both 2 insulin-resistant and to insulin-sensitive (athletes) states. The composition of this lipid store is 3 unknown in these states. 4 Design and Methods:We used a recently validated and potentially widely applicable 1 H 5 magnetic resonance spectroscopy method to compare the compositional saturation index 6 (CH2:CH3 ratio) and concentration independent of composition (CH3) of intramyocellular 7 lipid in the soleus and tibialis anterior muscles of 16 female insulin-resistant lipodystrophic 8 patients with that of age-and gender-matched athletes (n=14) and healthy controls (n = 41). 9Main Outcome: IMCL compositional saturation index (CH2:CH3 ratio). 10
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