Differentially expressed genes and morphological changes during lengthened immobilization in rat soleus muscle.
To examine the effect of lengthened immobilization on the expression of genes and concomitant morphological changes in soleus muscle, rat hindlimbs were immobilized at the ankle in full dorsiflexion by plaster cast. After removing the muscle (after 1 hr, 1, 4, and 7 days of immobilization), morphology and differential gene expression were analyzed through electron microscopy and differential display reverse transcription-polymerase chain reaction (DDRT-PCR), respectively. At the myotendinous junction (MTJ), a large cytoplasmic space appeared after 1 hr of immobilization and became enlarged over time, together with damaged Z lines. Interfibrillar space was detected after 1 day of immobilization, but diminished after 7 days. At the muscle belly, Z-line streaming and widening were observed following 1 hr of immobilization. Disorganization of myofilaments (misalignment of adjacent sarcomeres, distortion, or absence of Z lines) was detected after 4 days. Furthermore, mitochondrial swelling and cristae disruption were observed after 1 day of stretching. A set of 15 differentially expressed candidate genes was identified through DDRT-PCR. Of 11 known genes, seven (Atp5g3, TOM22, INrf2, Slc25a4, Hdac6, Tpm1, and Sv2b) were up and three (Podxl, Myh1, and Surf1) were down-regulated following immobilization. In the case of Acyp2, 1-day stretching-specific expression was observed. Atp5g3, Slc25a4, TOM22, and Surf1 are mitochondrial proteins related to energy metabolism, except TOM22, which has a chaperone-like activity located in the mitochondrial outer membrane. Together with these, INrf2, Hdac6, Podxl, and Acyp2 are related more or less to stress-induced apoptosis, indicating the responses to apoptotic changes in mitochondria caused by stretching. The expression of both Tpm1 and Myh1, fast twitch isoforms, suggests adaption to the immobilization. These results altogether indicate that lengthened immobilization regulates the expression of several stress/apoptosis-related and muscle-specific genes responsible for the slow-to-fast transition in soleus muscle despite profound muscle atrophy.
Kim
Ji Won
JW
Department of Physical Therapy, College of Health Science, Baekseok University, Cheonan, South Korea.
Kwon
Oh Yun
OY
Kim
Myoung Hee
MH
D000818:Animals; D020869:Gene Expression Profiling; D019417:Hindlimb Suspension; D007103:Immobilization / Q000009:adverse effects*; D017403:In Situ Hybridization; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000737:chemistry / Q000473:pathology; D018657:Muscle Fibers, Slow-Twitch / Q000737:chemistry / Q000473:pathology; D009124:Muscle Proteins / Q000235:genetics* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000254:growth & development / Q000294:innervation / Q000473:pathology*; D015347:RNA Probes; D051381:Rats; D017207:Rats, Sprague-Dawley
D009124:Muscle Proteins; D015347:RNA Probes