Development of the Thymus and Kidney and Effects of Resveratrol on Their Aging in a Short-Lived Fish.

Annual fishes of the genus Nothobranchius have been widely used in cognitive, behavioral, and genetic studies, and have become an excellent animal model for studying aging. However, the development and degeneration of immune organs in annual fishes and the antagonistic effects of resveratrol remain unclear. In the present study, the development of thymus and kidney was investigated systematically using Nothobranchius guentheri from larvae, juveniles, and young and old fish with hematoxylin and eosin staining. We found that thymus primordium was observed first in the larvae at 2 days after hatching (dah). After the lymphoid cells became evident at 5 dah, the thymus acquired an irregular shape at 7 dah. Then it formed a wedge shape at 15 dah. Thymus looked as homogeneous distribution of lymphocytes at 1 month old, and it differentiated into cortex and medulla approximately in 2-month-old fish. Combined with TUNEL and senescence-associated ß-galactosidase (SA-ß-gal) staining, it showed the degeneration of the thymus appeared in 4-month-old fish. Kidney primordium appeared on 1 dah, and the glomerulus was visible at 7 dah. The nephrogenic activity was most apparent in 1-month-old fish. A large hematopoietic tissue was arranged in the renal interstitium in 2- and 3-month-old fish. In 6-month-old fish, the kidney structure became less dense. By 12 months, the kidney exhibited the most pronounced histological characteristics of aging. Feeding resveratrol ameliorated renal fibrosis and SA-ß-gal staining with age, increased SIRT1 and SIRT3 expression, and decreased the levels of NF-κB and inflammatory factors in thymus and kidney of the fish. We provided basic data for the development and degeneration of immune organs and resveratrol's anti-aging effects in short-lived fish.

Metformin Protects Against Inflammation, Oxidative Stress to Delay Poly I:C-Induced Aging-Like Phenomena in the Gut of an Annual Fish.

Metformin, a clinical agent of type 2 diabetes, is reported as a potential geroprotector. Viral infection induces phenotypes of senescence in human T cells, and polyinosinic:polycytidylic acid (poly I:C), a viral mimic, induces upregulation of senescence-associated beta-galactosidase (SA-ß-gal) activity in the ovary of the annual fish Nothobranchius guentheri. However, the effects and mechanisms of metformin on poly I:C-induced aging-like phenomena are poorly understood in vertebrates. In this study, the activity of SA-ß-gal increased in the gut of 12-month-old fish and poly I:C-injected 6-month-old fish, compared to 6-month-old control fish, indicating that poly I:C induces aging-like phenomena in the gut of the fish. Metformin supplementation retarded accumulation of SA-ß-gal in the gut of old fish and poly I:C-treated young fish. The results of qPCR analysis showed that metformin reduced NF-κB-mediated inflammatory response including the decreased level of proinflammatory cytokine IL-8 and increased expression of anti-inflammatory cytokine IL-10 in the gut of the fish with natural aging and poly I:C-injected 6-month-old fish. Metformin also exhibited antioxidant effects, as it reduced reactive oxygen species production that is associated with the upregulation of FoxO3a and PGC-1α in the gut of 6-month-old fish with poly I:C injection. Expression of AMPK and SIRT1 was reduced in the gut of 6-month-old fish with poly I:C treatment, and feeding metformin reversed these declines. Taken together, the present study suggested that poly I:C injection led to aging-like phenomena in the gut and metformin activated AMPK and SIRT1 to reduce NF-κB-mediated inflammation and resist oxidative stress via enhanced expression of FoxO3a and PGC-1α and finally delayed gut aging in vertebrates.

Resveratrol reduces senescence-associated secretory phenotype by SIRT1/NF-κB pathway in gut of the annual fish Nothobranchius guentheri.

Senescent cells display a senescence-associated secretory phenotype (SASP), which contributes to aging. Resveratrol, an activator of SIRT1, has anti-aging, anti-inflammatory, anti-oxidant, anti-free radical and other pharmacological effects. The genus of the annual fish Nothobranchius has become an emerging animal model for studying aging. However, the underlying mechanism for resveratrol to delay aging by SASP regulation has not been elucidated in vertebrates. In this study, the annual fish N. guentheri were fed with resveratrol for long-term treatment. The results showed that resveratrol reversed intensive senescence-associated ß-galactosidase activity with aging process, down-regulated levels of SASP-associated proinflammatory cytokines IL-8 and TNFα, and up-regulated expression of anti-inflammatory cytokine IL-10 in gut of the fish. Resveratrol increased SIRT1 expression, and inhibited NF-κB by decreasing RelA/p65, Ac-RelA/p65 and p-IκBα levels and by increasing the interaction between SIRT1 and RelA/p65. Moreover, resveratrol reversed the decline of intestinal epithelial cells (IECs) and intestinal stem cells (ISCs) caused by aging in gut of the fish. Together, our results implied that resveratrol inhibited SASP through SIRT1/NF-κB signaling pathway and delayed aging of the annual fish N. guentheri.

Oogenesis, vitellogenin-mediated ovarian degeneration and immune response in the annual fish Nothobranchius guentheri.

Annual fishes of the genus Nothobranchius show expression of age-related biomarkers at behavioral and histological levels. They therefore represent an excellent animal model for aging studies. However, oocyte development, histological and biochemical degeneration and immune response of ovary in the annual fishes remain unclear. Here, using one of these short-lived fishes, Nothobranchius guentheri, we reported that oogenesis process was divided into four stages (oogonium, primary growth stage, cortical alveolus stage and vitellogenesis stage), and old ovaries showed histological degeneration (with decreased mature oocytes and increased atretic oocytes) accompaning with high levels of senescence-associated beta-galactosidase and lipofuscin by down-regulation of vitellogenin (the precursor of yolk proteins). Moreover, poly(I:C) induced inflammation with overexpression of NF-κB and IL-8, and up-regulated vitellogenin expression. It was a first analysis for vitellogenin to participate in ovarian degeneration and immune response in ovary of fish, indicating that vitellogenin fulfilled a critical role in ovary development and innate immune system.