A personal history of veterinary public health

GH indirectly enhances the regeneration of transgenic zebrafish fins through IGF2a and IGF2b

The somatotropic axis, composed essentially of the growth hormone (GH) and insulin-like growth factors (IGFs), is the main regulator of somatic growth in vertebrates. However, these protein hormones are also involved in various other major physiological processes. Although the importance of IGFs in mechanisms involving tissue regeneration has already been established, little is known regarding the direct effects of GH in these processes. In this study, we used a transgenic zebrafish (Danio rerio) model, which overexpresses GH from the beta-actin constitutive promoter. The regenerative ability of the caudal fin was assessed after repeated amputations, as well as the expression of genes related to the GH/IGF axis. The results revealed that GH overexpression increased the regenerated area of the caudal fin in transgenic fish after the second amputation. Transgenic fish also presented a decrease in gene expression of the GH receptor (ghrb), in opposition to the increased expression of the IGF1 receptors (igf1ra and igf1rb). These results suggest that transgenic fish have a higher sensitivity to IGFs than to GH during fin regeneration. With respect to the different IGFs produced locally, a decrease in igf1a expression and a significant increase in both igf2a and igf2b expression was observed, suggesting that igf1a is not directly involved in fin regeneration. Overall, the results revealed that excess GH enhances fin regeneration in zebrafish through igf2a and igf2b expression, acting indirectly on this major physiological process.

Capacity for recovery and possible mechanisms in immobilization atrophy of young and old animals

The effect of limb immobilization on muscle wasting and recovery of young and old rats was studied. Limb immobilization caused rapid and pronounced muscle weight loss, which was overcome efficiently in the muscles of young animals. However, muscles of old animals did not recover as well, indicating that muscle turnover (degradation and synthesis of proteins) is slower in old muscles than in young ones. The mechanisms of muscle wasting due to immobilization may involve two stages, the fast phase employing calcium-dependent proteolysis and the slower phase recruiting the lysosomal and ubiquitin-proteosome systems. The slow phase most probably involves the penetration of white cells between the muscle fibers and involves the secretion of cytokines that mediate a cascade of intracellular events, which culminates in muscle protein degradation. Thus, it was shown in our study and in other similar reports that through the influence of TNF-alpha and an increase in oxidative stress, there is marked activation of transcription factor NF-kappaB, which in turn induces many proteins to carry the signals that eventually result in protein breakdown. Because protein turnover was shown to slow down with age, it will be of great interest to study these events in aging muscles and to try to ascertain the specific events that make protein breakdown in aged muscles different from that in young ones.