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TENSION REDUCTION INDUCES SKELETAL MUSCLE ATROPHY IN A NOVEL IN VITRO GROUND BASED MODEL THAT CAN BE ATTENUATED BY HIGH LEVELS OF INSULIN. P.H.U. Lee, B.C. Creswick, M. Nackman, X. Wang and H.H. Vandenburgh. Dept. of Pathology, Brown Univ., Providence, RI

   Although tissue-engineered skeletal muscle constructs termed BioArtificial Muscles (BAMs) had demonstrated the direct effects of spaceflight on skeletal muscle atrophy on previous space shuttle missions (FASEB J 13, 1031; 1999), no ground based in vitro model of skeletal muscle atrophy currently exists. The objective of this study was to develop and test a ground based model for skeletal muscle atrophy using tension reduction in BAMs to complement spaceflight and ground studies and to test potential pharmacologic countermeasures.

   BAMs made from primary adult mouse myoblasts were tissue-engineered so that active forces generated in response to electrical stimuli can be measured. BAMs ranging from 2-4 weeks in age were reduced in length by 50% or released at one end for at least 7 days and incubated in regular growth medium (GM), or supplemented medium (SM) containing insulin (10 μg/ml)  and FGF (0.2 ng/ml). 

   Compared to controls, after tension reduction in GM, maximum isometric tetanic forces decreased significantly by 21 to 50% in the four experiments, and in separate experiments, the mean myofiber cross-sectional area (CSA) was reduced by 10% (p<0.05), total non-collagenous protein content decreased by 8.7% (p<0.05), and the 6 hr incorporation of C¹⁴-phenylalanine decreased by 22% (p<0.05).  Compared to tension reduced BAMs in GM, peak active forces increased 43 to 76%, protein content increased 4% (p=0.09), and myofiber CSA increased 20% (p<0.05) when incubated in SM.

   These data demonstrate that reducing tension in BAMs induces skeletal muscle atrophy, possibly by decreasing protein synthesis rates. Additionally, high levels of insulin, likely interacting with IGF-1 receptors, may attenuate the induced atrophy.  Further development and utilization of this novel in vitro model of skeletal muscle atrophy may reveal mechanisms of atrophy both on Earth and in spaceflight.

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