Quantifiable Biomarkers of Normal Aging in the Japanese Medaka Fish (Oryzias latipes)

BACKGROUND: Small laboratory fish share many anatomical and histological characteristics with other vertebrates, yet can be maintained in large numbers at low cost for lifetime studies. Here we characterize biomarkers associated with normal aging in the Japanese medaka (Oryzias latipes), a species that has been widely used in toxicology studies and has potential utility as a model organism for experimental aging research. PRINCIPAL FINDINGS: The median lifespan of medaka was approximately 22 months under laboratory conditions. We performed quantitative histological analysis of tissues from age-grouped individuals representing young adults (6 months old), mature adults (16 months old), and adults that had survived beyond the median lifespan (24 months). Livers of 24-month old individuals showed extensive morphologic changes, including spongiosis hepatis, steatosis, ballooning degeneration, inflammation, and nuclear pyknosis. There were also phagolysosomes, vacuoles, and residual bodies in parenchymal cells and congestion of sinusoidal vessels. Livers of aged individuals were characterized by increases in lipofuscin deposits and in the number of TUNEL-positive apoptotic cells. Some of these degenerative characteristics were seen, to a lesser extent, in the livers of 16-month old individuals, but not in 6-month old individuals. The basal layer of the dermis showed an age-dependent decline in the number of dividing cells and an increase in senescence-associated β-galactosidase. The hearts of aged individuals were characterized by fibrosis and lipofuscin deposition. There was also a loss of pigmented cells from the retinal epithelium. By contrast, age-associated changes were not apparent in skeletal muscle, the ocular lens, or the brain. SIGNIFICANCE: The results provide a set of markers that can be used to trace the process of normal tissue aging in medaka and to evaluate the effect of environmental stressors

Reflectance-Based Vegetation Index Assessment of Four Plant Species Exposed to Lithium Chloride

This study considers whether a relationship exists between response to lithium (Li) exposure and select vegetation indices (VI) determined from reflectance spectra in each of four plant species: Arabidopsis thaliana, Helianthus annuus (sunflower), Brassica napus (rape), and Zea mays (corn). Reflectance spectra were collected every week for three weeks using an ASD FieldSpec Pro spectroradiometer with both a contact probe (CP) and a field of view probe (FOV) for plants treated twice weekly in a laboratory setting with 0 mM (control) or 15 mM of lithium chloride (LiCl) solution. Plants were harvested each week after spectra collection for determination of relevant physical endpoints such as relative water content and chlorophyll content. Mixed effects analyses were conducted on selected endpoints and vegetation indices (VI) to determine the significance of the effects of treatment level and length of treatment as well as to determine which VI would be appropriate predictors of treatment-dependent endpoints. Of the species considered, A. thaliana exhibited the most significant effects and corresponding shifts in reflectance spectra. Depending on the species and endpoint, the most relevant VIs in this study were NDVI, PSND, YI, R1676/R1933, R750/R550, and R950/R750

Histology of retina.

<p>Each panel is a transverse section of a similar region of the retina. Paraffin embedded sections were stained with hematoxylin and eosin as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013287#s4" target="_blank">Materials and Methods</a>. Cell layers are indicated at right: GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; IS/OS– inner segment/outer segment of the photoreceptor cells; RPE/C, retinal pigment epithelium/cells. Arrowheads in center and right panel indicated regions where pigmented cells have been lost.</p

BrdU incorporation and senescence-associated β-galactosidase activity in skin and skeletal muscle.

<p>Each panel is a transverse section showing skeletal muscle (at top) and skin (at bottom). Cryosections were prepared and stained as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013287#s4" target="_blank">Materials and Methods</a>. (<b>A</b>) Senescence-associated β-galactosidase detected by histochemical analysis using X-gal substrate (blue staining). Positive areas are denoted by white arrows. Tissue was counterstained with eosin. Insets show higher magnification views of boxed regions. (<b>B</b>) BrdU incorporation detected by immunofluorescence (green channel). Positive cells are denoted by white arrows. Nuclei were counterstained with 7-amino actinomycin D (7-AAD) (red channel). (<b>C</b>) BrdU-positive cells per field were quantified as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013287#s4" target="_blank">Materials and Methods</a>. Error bars denote standard deviation. Significance was determined based on Student's <i>t</i>-test (**, <i>P</i><0.01). Each field is 2.26×10⁵ µm².</p