Skeletal muscle remodeling in response to alpine skiing training in older individuals.

This study investigated whether regular alpine skiing could reverse sarcopenia and muscle weakness in older individuals. Twenty-two older men and women (67 ± 2 years) underwent 12 weeks of recreational skiing, two to three times a week, each session lasting ∼ 3.5 h. An age-matched, inactive group (n=20, 67 ± 4 years) served as a control (CTRL). Before and after the training period, knee extensors muscle thickness (T(m) ), pennation angle (θ) and fascicle length (L(f) ) of the vastus lateralis muscle were measured by ultrasound. Maximum isokinetic knee extensor torque (MIT) at an angular velocity of 60°/s was measured by dynamometry. After the training, T(m) increased by 7.1% (P<0.001), L(f) by 5.4% (P<0.02) and θ by 3.4% (P<0.05). The increase in T(m) was matched by a significant gain in MIT (13.3%, P<0.001). No significant changes, except for a decrease in θ (2.1%, P<0.02), were found in the CTRL group. The gain in T(m) in the training group correlated significantly with an increase in the focal adhesion kinase content, pointing to a primary role of this mechano-sensitive protein in sarcomere remodeling with muscle hypertrophy. Overall, the results show that alpine skiing is an effective intervention for combating sarcopenia and weakness in old age.

Load-sensitive adhesion factor expression in the elderly with skiing: relation to fiber type and muscle strength.

We hypothesized that 12 weeks of downhill skiing mitigates the functional deficits of knee extensor muscles in elderly subjects due to the specific recruitment of fast motor units during forceful turns on the slope. Downhill skiing led to a 1.4-fold increase in the mean cross-sectional area of slow (P=0.04)- and fast (P=0.08)-type muscle fibers. Fold changes in the expression of the structural component of focal adhesions, gamma-vinculin, were correlated with alterations in concentric force (r=0.64). Hypertrophy of fast fibers was more pronounced in women than in men (1.7 vs 1.1). Gender-specific structural-functional adjustments of knee extensor muscles and attached patellar tendon were reflected by altered expression of pro- vs de-adhesive proteins and a number of correlations. The de-adhesive protein tenascin-C was selectively increased in women compared with men (1.7 vs 1.1) while the content of the adhesive collagen XII was specifically reduced in women. The pro-adhesive focal adhesion kinase showed a specific increase in men compared with women (1.9 vs 1.1). Our findings indicate that quantitatively matched adaptations in slow and fast motor units of extensor muscle underlie the preventive effect of skiing against sarcopenia and support that hypertrophy and reinforcement of fiber adhesion operate in the improvement of muscle strength.

Protein tyrosine kinase expression during the estrous cycle and carcinogenesis of the mammary gland.

The susceptibility of the mammary epithelium to neoplastic transformation is linked to the exposure to estrogen during the estrous cycle. The effects of the estrous cycle on the mouse mammary gland have been investigated by analyzing 3H-thymidine incorporation, milk protein gene expression and DNA fragmentation. We found that the mammary epithelium undergoes limited proliferation, differentiation and apoptosis in a cycle-dependent manner. The estrous-responsive regulators of the mammary epithelium are unknown; however, considering the integral role of protein tyrosine kinases (PTKs) in the control of normal and malignant development, members of this family of enzymes are likely candidates for such regulatory molecules. Using a RT-PCR-based cloning strategy, we have undertaken a survey of PTKs expressed in the mammary gland at defined stages of development, with special emphasis on the estrous cycle. We identified 21 known and 4 novel PTKs. Their expression was analyzed throughout mammary gland development and in mammary neoplasias using a transgenic mouse model for invasive and non-invasive carcinogenesis. Most of the identified PTKs showed highest expression during the estrous cycle and were down-regulated during pregnancy and lactation. Deregulated expression was rarely observed in the non-invasive mammary tumors. In contrast, 10 of 19 PTKs expressed during the estrous cycle were also over-expressed in the invasive carcinomas, mostly involving members of the receptor family of PTKs.