The use of mature zebrafish (Danio rerio) as a model for human aging and disease.

Zebrafish (Danio rerio) have been extensively utilized for understanding mechanisms of development. These studies have led to a wealth of resources including genetic tools, informational databases, and husbandry methods. In spite of all these resources, zebrafish have been underutilized for exploring pathophysiology of disease and the aging process. Zebrafish offer several advantages over mammalian models for these studies, including the ability to perform saturation mutagenesis and the capability to contain thousands of animals in a small space. In this review, we will discuss the use of mature zebrafish as an animal model and provide specific examples to support this novel use of zebrafish. Examples include demonstrating that clinical pathology can be performed in mature zebrafish and that age-associated changes in heat shock response can be observed in zebrafish. These highlights demonstrate the utility of zebrafish as a model for disease and aging.

In vivo visualization of aging-associated gene transcription: evidence for free radical theory of aging.

The expression of a variety of proteins is elevated with aging through unknown mechanisms. The free radical theory of aging promulgates that reactive oxygen species (ROS) promote the aging process. However, the mechanisms as to how ROS contribute to the aging process are not clear. We present data here that demonstrate that aging induced ROS promote aging-associated interleukin-6 (IL-6) gene transcription in mice that are transgenic for the murine IL-6 promoter driving a luciferase reporter cDNA. N-acetylcysteine (NAC), an antioxidant, completely reverses the increased endogenous IL-6 promoter activity in the old mice determined by real-time bioluminescence imaging (BLI). We conclude that ability of ROS to act as secondary messengers and induce gene expression may contribute to the aging process.

Characterization of the heat shock response in mature zebrafish (Danio rerio).

Heat shock proteins (Hsps) are involved in many physiological and pathological processes and are diminished with age in a variety of species. As zebrafish embryos have proven to be excellent models for studying Hsp response during development, we sought to characterize the response in mature zebrafish to demonstrate the utility of the zebrafish model in studying late-life diseases and the biology of aging. Accordingly, mature zebrafish were exposed to a 37 degrees C heat stress and mRNA was isolated from various tissues and subjected to analysis by RT-PCR. We found that Hsp70 was upregulated in brain, liver, and muscle, while Hsp47 was upregulated in brain, but not liver or muscle. Hsp90alpha, Hsp90beta, and heat shock factor 1a (Hsf1a) were expressed in all three tissues, but were not upregulated in response to heat stress. A comparison of Hsp expression in young versus mature zebrafish revealed decreased basal levels of Hsp70 and increased levels of Hsf1a in mature fish. These results indicate that the heat shock response is detectable in mature zebrafish and that there are age differences in their heat shock response, suggesting that mature zebrafish may be a useful model for studying Hsp response during the aging process.

Hematologic and serum biochemical values for zebrafish (Danio rerio).

The zebrafish (Danio rerio) has proven an excellent model for study of vertebrate development and genetics. Mutagenesis studies have produced many blood mutants with defects ranging from hematopoiesis to coagulation. The overwhelming majority of zebrafish studies have focused on development and mutational effects in embryos, whereas effects in mature zebrafish have gone largely unexplored. We believe that zebrafish will prove a valuable model for study of aging and age-related diseases, and we have sought to characterize some of the basic features of mature zebrafish. Accordingly, blood was collected from adult zebrafish and was analyzed to determine reference hematologic and biochemical parameters. White blood cell differential counts indicated predominantly lymphocytes, with mean proportion of 82.95%. Total red blood cell counts averaged 3.02 x 10(6) cells/microl. Except for increases in alanine transaminase (ALT), amylase, and phosphorus values, serum biochemical analytes were within the range of reported values for mammals and other species of fish. Accurate analysis of the many zebrafish mutants generated requires determination of normal characteristics of zebrafish. We believe results such as these will help define normal adult zebrafish, which have a tremendous potential for use in the study of human disease and aging.

Osteoprotegerin abrogates chronic alcohol ingestion-induced bone loss in mice.

To investigate the role of osteoprotegerin (OPG) on alcohol (ethanol)-mediated osteoporosis, we measured a variety of bone remodeling parameters in mice that were either on a control diet, an ethanol (5%) diet, or an ethanol (5%) diet plus OPG administration. OPG diminished the ethanol-induced (1) decrease in bone mineral density (BMD) as determined by dual-energy densitometry, (2) decrease in cancellous bone volume and trabecular width and the increase of osteoclast surface as determined by histomorphometry of the femur, (3) increase in urinary deoxypyridinolines (Dpd's) as determined by ELISA, and (4) increase in colony-forming unit-granulocyte macrophage (CFU-GM) formation and osteoclastogenesis as determined by ex vivo bone marrow cell cultures. Additionally, OPG diminished the ethanol-induced decrease of several osteoblastic parameters including osteoblast formation and osteoblast culture calcium retention. These findings were supported by histomorphometric indices in the distal femur. Taken together, these data show that OPG diminishes ethanol-induced bone loss. Furthermore, they suggest that OPG achieves this through its ability to abrogate ethanol-induced promotion of osteoclastogenesis and promote osteoblast proliferation.

Effects of Lactobacillus spp. on Cytokine Production by RAW 264.7 Macrophage and EL-4 Thymoma Cell Lines.

We have hypothesized that lactobacilli used in fermented dairy products can stimulate immune function via enhancing cytokine secretion by leukocytes. To test the effects of lactobacilli on cytokine production, RAW 264.7 cells (macrophage model) and EL4.IL-2 thymoma cells (T helper cell model) were cultured in the presence of 16 representative strains of heat-killed Lactobacillus spp. cells. In unstimulated RAW 264.7 cells, most lactobacilli, when present at concentrations from 106 to 108 bacterial cells per ml, induced marked tumor necrosis factor alpha (TNF-α) production (up to 411-fold) compared to the negligible TNF-α in controls. A strain-dependent increase in interleukin 6 (IL-6) production (up to 88-fold) was also observed without stimulation at concentrations of 108 bacteria per ml. Upon concurrent stimulation of RAW 264.7 cells with lipopolysaccharide, both IL-6 and TNF-α production were enhanced between 4.2- and 10.6-fold and 1.8- and 8.7-fold, respectively, when cultured with 108 lactobacilli per ml. In unstimulated EL4.IL-2 cells, lactobacilli had no effect on interleukin 2 (IL-2) or interleukin 5 (IL-5) production. Upon stimulation of EL4.IL-2 cells with phorbol 12-myristate-13-acetate, IL-2 secretion increased up to 1.9-fold in the presence of 106 L. bulgaricus Lr 79 cells per ml whereas this cytokine decreased in the presence of 107 or 108 lactobacilli per ml. In contrast, IL-5 secretion increased in the presence of increasing concentrations of lactobacilli (up to 3.1-fold with 108 L. bulgaricus NCK 231 cells per ml). The results indicated that direct interaction of most lactobacilli with macrophages resulted in a concentration-dependent enhancement of cytokine production, whereas the effects on cytokine production by the T-cell model were smaller and strain dependent. The in vitro approaches employed here should be useful in further characterization of the effects of lactobacilli on the gut and systemic immune systems.