Endocrine Actions of Osteocalcin

Osteocalcin is the most abundant noncollagenous protein of bone matrix. Once transcribed, this protein undergoes posttranslational modifications within osteoblastic cells before its secretion, including the carboxylation of three glutamic residues in glutamic acid, which is essential for hydroxyapatite binding and deposition in the extracellular matrix of bone. Recent provocative data from experimental observations in mice showed that the circulating undercarboxylated fraction of osteocalcin increases insulin secretion and sensitivity, lowers blood glucose, and decreases visceral fat in both genders, while it enhances testosterone production by the testes in males. Moreover, both total and undercarboxylated osteocalcins increase following physical activity with potential positive effects on glucose tolerance. Despite that these evidences have been only in part confirmed in humans, further prospective investigations are needed to definitively establish the endocrine role of osteocalcin both in the general population and cohorts of patients with diabetes or other metabolic disorders.

THE EFFECTS OF GROWTH FACTORS ON PROLIFERATION AND MATRIX SYNTHESIS OF FIBROBLASTS FROM GOAT MEDIAL COLLATERAL LIGAMENT

Growth factors have been shown to play a critical role in enhancing tissue healing. In this study, we evaluate the effect of growth factors on cell proliferation and matrix synthesis. Fibroblasts were derived from medial collateral ligaments (MCLs) of goats and grown in culture. Basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF-BB), epidermal growth factor (EGF), and transforming growth factor ( TGF -β1) were used for the treatment of cells. It was found that bFGF, PDGF-BB and EGF significantly increased proliferation of the goat MCL fibroblasts. In addition, among these three growth factors, bFGF, at the concentration of 1.0 ng/ml, had the maximal effect on cell proliferation. Furthermore, both TGF -β1 and EGF significantly increased collagen and noncollagenous protein syntheses of goat MCL fibroblasts. The results of this study may be used as baseline data for the application of growth factors to enhance MCL healing in a goat model.

Eccentric exercise training as a countermeasure to non-weight-bearing soleus muscle atrophy

Although various exercise paradigms have been tested, none has completely prevented muscle atrophy during non-weight bearing. Because loaded eccentric contractions occur during normal daily activity but are absent during non-weight bearing, this investigation tested whether eccentric resistance training could prevent soleus muscle atrophy during non-weight bearing. Adult female rats were randomly assigned to either weight bearing +/- intramuscular electrodes or non-weight bearing +/- intramuscular electrodes groups. Electrically stimulated maximal eccentric contractions (4 sets of 6 repetitions at approximately 0.2 fiber lengths/s, 128 degrees range of motion) were performed on anesthetized animals at 48-h intervals during the 10-day experiment. Non-weight bearing significantly reduced soleus muscle wet weight (28–31%) and noncollagenous protein content (30–31%) compared with controls. Eccentric exercise training during non-weight bearing attenuated but did not prevent the loss of soleus muscle wet weight and noncollagenous protein by 77 and 44%, respectively. The potential of eccentric exercise training as an effective and highly efficient counter-measure to non-weight-bearing atrophy is demonstrated in the 44% attenuation of soleus muscle noncollagenous protein loss by eccentric exercise during only 0.035% of the total non-weight-bearing time period.