TY - JOUR

T1 - Expression of insulin-like growth factor I, insulin-like growth factor binding proteins, and collagen mRNA in mechanically loaded plantaris tendon

AU - Olesen, Jens L

AU - Heinemeier, Katja M

AU - Haddad, Fadia

AU - Langberg, Henning

AU - Flyvbjerg, Allan

AU - Kjaer, Michael

AU - Baldwin, Kenneth M

PY - 2006

Y1 - 2006

N2 - Insulin-like growth factor I (IGF-I) is known to exert an anabolic effect on tendon fibroblast production of collagen. IGF-I's regulation is complex and involves six different IGF binding proteins (IGFBPs). Of these, IGFBP-4 and -5 could potentially influence the effect of IGF-I in the tendon because they both are produced in fibroblast; however, the response of IGFBP-4 and -5 to mechanical loading and their role in IGF-I regulation in tendinous tissue are unknown. A splice variant of IGF-I, mechano-growth factor (MGF) is upregulated and known to be important for adaptation in loaded muscle. However, it is not known whether MGF is expressed and upregulated in mechanically loaded tendon. This study examined the effect of mechanical load on tendon collagen mRNA in relation to changes in the IGF-I systems mRNA expression. Data were collected at 2, 4, 8 and 16 days after surgical removal of synergistic muscle to the plantaris muscle of the rat, thus increasing the load to plantaris muscle and tendon. Nearly a doubling of the tendon mass was observed after 16 days of loading. A rapid rise in tendon procollagen III mRNA was seen after 2 days whereas the increase in procollagen I mRNA was significant from day 8. MGF was expressed and upregulated in loaded tendon tissue with a faster response than IGF-I, which was increased from day 8. Finally, IGFBP-4 mRNA was increased with a time pattern similar to procollagen III, whereas IGFBP-5 decreased at day 8. In conclusion, loading of tendon tissue results in an upregulation of IGF-I, IGFBP-4, and procollagen and is associated with an increase in tendon mass. Also, MGF is expressed with an early upregulation in loaded tendon tissue. We suggest that the IGF-I system could be involved in collagen synthesis in tendon in response to mechanical loading.

AB - Insulin-like growth factor I (IGF-I) is known to exert an anabolic effect on tendon fibroblast production of collagen. IGF-I's regulation is complex and involves six different IGF binding proteins (IGFBPs). Of these, IGFBP-4 and -5 could potentially influence the effect of IGF-I in the tendon because they both are produced in fibroblast; however, the response of IGFBP-4 and -5 to mechanical loading and their role in IGF-I regulation in tendinous tissue are unknown. A splice variant of IGF-I, mechano-growth factor (MGF) is upregulated and known to be important for adaptation in loaded muscle. However, it is not known whether MGF is expressed and upregulated in mechanically loaded tendon. This study examined the effect of mechanical load on tendon collagen mRNA in relation to changes in the IGF-I systems mRNA expression. Data were collected at 2, 4, 8 and 16 days after surgical removal of synergistic muscle to the plantaris muscle of the rat, thus increasing the load to plantaris muscle and tendon. Nearly a doubling of the tendon mass was observed after 16 days of loading. A rapid rise in tendon procollagen III mRNA was seen after 2 days whereas the increase in procollagen I mRNA was significant from day 8. MGF was expressed and upregulated in loaded tendon tissue with a faster response than IGF-I, which was increased from day 8. Finally, IGFBP-4 mRNA was increased with a time pattern similar to procollagen III, whereas IGFBP-5 decreased at day 8. In conclusion, loading of tendon tissue results in an upregulation of IGF-I, IGFBP-4, and procollagen and is associated with an increase in tendon mass. Also, MGF is expressed with an early upregulation in loaded tendon tissue. We suggest that the IGF-I system could be involved in collagen synthesis in tendon in response to mechanical loading.

KW - Animals

KW - Biomechanics

KW - Collagen

KW - Female

KW - Gene Expression Regulation

KW - Insulin-Like Growth Factor Binding Protein 4

KW - Insulin-Like Growth Factor Binding Protein 5

KW - Insulin-Like Growth Factor Binding Proteins

KW - Insulin-Like Growth Factor I

KW - Muscle, Skeletal

KW - Procollagen

KW - Protein Isoforms

KW - RNA, Messenger

KW - Rats

KW - Rats, Sprague-Dawley

KW - Tendons

KW - Time Factors

KW - Up-Regulation

KW - Weight-Bearing

U2 - 10.1152/japplphysiol.00636.2005

DO - 10.1152/japplphysiol.00636.2005

M3 - Journal article

C2 - 16782835

VL - 101

SP - 183

EP - 178

JO - Journal of Applied Physiology

JF - Journal of Applied Physiology

SN - 8750-7587

IS - 1

ER -