Tendon and skeletal muscle matrix gene expression and functional responses to immobilisation and rehabilitation in young males: effect of growth hormone administration

Abstract

We examined the effect of growth hormone (GH) on connective tissue of tendon and skeletal muscle during immobilisation and re-training in humans. Young men (20-30 years; n = 20) were randomly assigned to daily recombinant human GH (rhGH) (33-50 μg kg(-1) day(-1)) or placebo (Plc), and had one leg immobilised for 2 weeks, followed by 6 weeks of strength training. The cross-sectional area (CSA), maximal muscle strength (maximal voluntary contraction, MVC) and biomechanical properties of the quadriceps muscle and patellar tendon were determined. Muscle and tendon biopsies were analysed for mRNA of collagen (COL1A1/3A1), insulin-like growth factors (IGF-1Ea/Ec), lysyl oxidase (LOX), matrix metalloproteases (MMP-2 and MMP-9), decorin and tenascin-C. Fibril morphology was analysed by transmission electron microscopy (TEM) to detect changes in the fibril diameter distribution. In muscle, CSA and MVC declined with immobilisation and recovered with rehabilitation similarly in both groups. Likewise, both groups showed increased IGF-1Ea/Ec and COL1A1/3A1 expression in muscle during re-training after immobilisation compared with baseline, and the increase was more pronounced when subjects received GH. The tendon CSA did not change during immobilisation, but increased in both groups during 6 weeks of rehabilitation (∼14%). A decline in tendon stiffness after immobilisation was observed only in the Plc group, and an increase during 6 weeks of rehabilitation was observed only in the GH group. IGF-1Ea and COL1A1/3A1 mRNA increased with immobilisation in the GH group only, and LOX mRNA was higher in the GH group than in the Plc group after immobilisation. Both groups showed an increase in MMP-2 with immobilisation, whereas no changes in MMP-9, decorin and tenascin-C were observed. The tendon fibril diameter distribution remained unchanged in both groups. In conclusion, GH stimulates collagen expression in both skeletal muscle and tendon, abolishes the normal inactivity-related decline in tendon stiffness and LOX, and results in increased tendon CSA and stiffness during rehabilitation. GH has a matrix-stabilising effect during periods of inactivity and rehabilitation in humans.

Figure 1. Circulating serum concentrations of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) during 2 weeks of immobilisation and 6 weeks of re-training in young males (n= 20) with either recombinant human GH (rhGH) (n= 10) or placebo (n= 10)

A, serum GH. B, serum IGF-1. Data are geometric means ± SEM.

Figure 2. Changes in cross-sectional area (CSA) (muscle and patellar tendon) and maximal muscle strength during 2 weeks of immobilisation and 6 weeks of re-training in young males (n= 20) with either recombinant human growth hormone (rhGH) (n= 10) or placebo (n= 10)

A, CSA of the quadriceps muscle; time effect (P < 0.01) and group interaction (P= 0.09). B, CSA of the patellar tendon; time effect (P < 0.01) and group interaction (P < 0.05). C, maximal isometric muscle strength; time effect (P < 0.01) and group interaction (P= 0.09). *Time effect, P < 0.05, compared with baseline (both groups). $Time effect, P < 0.05, compared with Post immob (both groups). §Time effect, P < 0.05, baseline/Post immob. vs. 2 weeks of re-training (GH). Data are means ± SEM.

Figure 3. Changes in patellar tendon biomechanical properties during 2 weeks of immobilisation and 6 weeks of re-training in young males (n= 20) with either recombinant human growth hormone (rhGH) (n= 10) or placebo (n= 10)

A, patellar tendon stiffness; time effect (P < 0.05) and group interaction (P < 0.05). B, patellar tendon Young's modulus; time effect (P < 0.05) and group interaction (P= 0.06). *Time effect, P < 0.05, compared with baseline (Plc). $Time effect, P < 0.05, from baseline, Post immob and 2 weeks of training (GH). §Group effect, P < 0.05, GH vs. Plc within time point. Data are means ± SEM.

Figure 4. Muscle insulin-like growth factor-1 (IGF-1) and collagen (COL) mRNA expression during 2 weeks of immobilisation and 6 weeks of re-training in young males (n= 20) with either recombinant human growth hormone (rhGH) (n= 10) or placebo (n= 10)

A, IGF-1Ea mRNA (muscle); time effect (P < 0.05) and group interaction (P < 0.05). B, IGF-1Ec mRNA (muscle); time effect (P < 0.05) and group interaction (P < 0.05). C, COL1A1 mRNA (muscle); time effect (P < 0.05) and group interaction (P < 0.05). D, COL3A1 mRNA (muscle); time effect (P < 0.05) and group interaction, (P < 0.05). *Time effect, P < 0.05, compared with baseline. $Group effect, P < 0.05, GH vs. Plc within time point. Data are geometric means ± SEM.

Figure 5. Tendon insulin-like growth factor-1 (IGF-1) and collagen (COL) mRNA expression during 2 weeks of immobilisation in young males (n= 20) with either recombinant human growth hormone (rhGH) (n= 10) or placebo (n= 10)

A, IGF-1Ea mRNA (tendon); time effect (P < 0.05) and group interaction (P < 0.05). B, COL1A1 mRNA (tendon); time effect (P= 0.07) and group interaction (P < 0.05). C, COL3A1 (tendon); time effect (P= 0.1) and group interaction, (P < 0.05). *Time effect, P < 0.05, compared with baseline (GH). $Group effect, P < 0.05, GH vs. Plc within time point. Data are geometric means ± SEM.

Figure 6. Tendon lysyl oxidase (LOX), matrix metalloprotease-2 (MMP-2), matrix metalloprotease-9, decorin and tenascin-C mRNA expression during 2 weeks of immobilisation in young males (n= 20) with either recombinant human growth hormone (rhGH) (n= 10) or placebo (n= 10)

A, LOX mRNA (tendon); time effect (P= 0.5) and group interaction (P < 0.05). B, MMP-2 mRNA (tendon); time effect (P < 0.05) and group interaction (P= 0.2). C, MMP-9 mRNA (tendon); time effect (P= 0.9) and group interaction (P= 0.7). D, decorin (tendon); time effect (P= 0.5) and group interaction (P= 0.8). E, tenascin-C (tendon); time effect (P= 0.7) and group interaction (P= 0.6). *Time effect, P < 0.05, compared with baseline. $Group effect, P < 0.05, GH vs. Plc. within time point. Data are geometric means ± SEM.

Figure 7. Absolute tendon fibril diameter distribution during 2 weeks of immobilisation and after 6 weeks of re-training in young males (n= 20) with either recombinant human growth hormone (rhGH) (n= 10) or placebo (n= 10)

A, fibril diameter distribution of the GH and placebo groups at baseline. B, fibril diameter distribution of the GH and placebo groups after 2 weeks of immobilisation (Post immob). C, fibril diameter distribution of the GH and placebo groups after 6 weeks of training. No time effect or group interactions were seen within time points. Data are means ± SEM.