Increased satellite cell apoptosis in vastus lateralis muscle after anterior cruciate ligament reconstruction.

OBJECTIVE: Recovery of the quadriceps femoris muscle after anterior ligament reconstruction is im-paired. The aim of this study was to investigate satellite cell content and function of the vastus lateralis muscle after anterior ligament reconstruction. METHODS: Biopsies were obtained from the vastus lateralis muscle of 16 recreational athletes immediately before and again 12 weeks after anterior ligament reconstruction. Total satellite cell number (Pax7+), activated (Pax7+/MyoD+), differentiating (Pax7-/MyoD+), and apoptotic (Pax7+/TUNEL+) satellite cells, myofibers expressing myosin heavy chain (MHC) I and II, and neonatal MHC (MHCneo) were determined immunohistochemically. RESULTS: After anterior ligament reconstruction, the number of apoptotic satellite cells was significantly (p = 0.019) increased, concomitant with a significant (p < 0.001) decrease in total satellite cell number, with no change in activated and differentiating satellite cell number. MHCneo+ myofibers tended towards an increase. CONCLUSION: Satellite cell apoptosis and the reduction in the satellite cell pool might provide an explanation for prolonged quadriceps muscle atrophy after anterior ligament reconstruction.

Gene expression changes in vastus lateralis muscle after different strength training regimes during rehabilitation following anterior cruciate ligament reconstruction.

Impaired muscle regeneration has repeatedly been described after anterior cruciate ligament reconstruction (ACL-R). The results of recent studies provided some evidence for negative alterations in knee extensor muscles after ACL-R causing persisting strength deficits in spite of the regain of muscle mass. Accordingly, we observed that 12 weeks of concentric/eccentric quadriceps strength training with eccentric overload (CON/ECC+) induced a significantly greater hypertrophy of the atrophied quadriceps muscle after ACL-R than conventional concentric/eccentric quadriceps strength training (CON/ECC). However, strength deficits persisted and there was an unexpected increase in the proportion of slow type I fibers instead of the expected shift towards a faster muscle phenotype after CON/ECC+. In order to shed further light on muscle recovery after ACL-R, the steady-state levels of 84 marker mRNAs were analyzed in biopsies obtained from the vastus lateralis muscle of 31 subjects before and after 12 weeks of CON/ECC+ (n = 18) or CON/ECC strength training (n = 13) during rehabilitation after ACL-R using a custom RT2 Profiler PCR array. Significant (p < 0.05) changes were detected in the expression of 26 mRNAs, several of them involved in muscle wasting/atrophy. A different pattern with regard to the strength training mode was observed for 16 mRNAs, indicating an enhanced hypertrophic stimulus, mechanical sensing or fast contractility after CON/ECC+. The effects of the type of autograft (quadriceps, QUAD, n = 19, or semitendinosus tendon, SEMI, n = 12) were reflected in the lower expression of 6 mRNAs involved in skeletal muscle hypertrophy or contractility in QUAD. In conclusion, the greater hypertrophic stimulus and mechanical stress induced by CON/ECC+ and a beginning shift towards a faster muscle phenotype after CON/ECC+ might be indicated by significant gene expression changes as well as still ongoing muscle wasting processes and a negative impact of QUAD autograft.

Strength Training Effects on Muscular Regeneration after ACL Reconstruction.

PURPOSE: Protracted quadriceps muscle atrophy is observed after anterior cruciate ligament reconstruction (ACL-R). The aim of this study was to assess if quadriceps strength training with eccentric overload (CON/ECC) is more efficient to induce muscle regeneration after ACL-R than conventional concentric/eccentric (CON/ECC) strength training. METHODS: Biopsies from the vastus lateralis muscle were obtained from 37 recreational athletes after 12 wk of regular rehabilitation after ACL-R and again after 12 wk with twice a week of either conventional CON/ECC (n = 16) or CON/ECC (n = 21) one-legged supervised leg-press training. Immunohistochemical analyses were used to determine satellite cell (SC) number (Pax7); activated SC number (Pax7/MyoD); fibers expressing myosin heavy-chain (MHC) I and II, MHC neonatal, and fiber cross-sectional area. Magnetic resonance imaging was performed to measure quadriceps cross-sectional area and isokinetic testing for the measurement of quadriceps strength. RESULTS: CON/ECC induced a significantly (P = 0.002) greater increase in quadriceps cross-sectional area than did CON/ECC. There also was a significant increase in the fiber cross-sectional areas of all fiber types and in quadriceps strength, but without significant difference between training groups. Only CON/ECC training led to a significant (P < 0.05) increase in percent type I fibers. After training, the number of MHC I/MHCneo fibers was significantly (P < 0.05) greater in the CON/ECC than after in the CON/ECC group. The proportion of hybrid fibers tended to decrease in both groups; percent type II fibers, SC number, and activated SC number remained unchanged. CONCLUSIONS: CON/ECC leads to significantly greater muscle hypertrophy compared with CON/ECC, but without the hypothesized enhancing effect on SC activation. At the same time, CON/ECC+ induces a less favorable slower muscle phenotype for strong and fast movements.