Probes for INS

Age-associated reduced motivation is a hallmark of neuropsychiatric disorders in the elderly. In our rapidly aging societies, it is critical to keep motivation levels high enough to promote healthspan and lifespan. However, how motivation is reduced during aging remains unknown. Here, we used multiple mouse models to evaluate motivation and related affective states in young and old mice. We also compared the effect of social isolation, a common stressor, to those of aging. We found that both social isolation and aging decreased motivation in mice, but that Bdnf expression in the ventral tegmental area (VTA) was selectively decreased during aging. Furthermore, VTA-specific Bdnf knockdown in young mice recapitulated reduced motivation observed in old mice. These results demonstrate that maintaining Bdnf expression in the VTA could promote motivation to engage in effortful activities and potentially prevent age-associated neuropsychiatric disorders.

A major limitation of mechanistic studies in aging brains is the lack of routine methods to robustly visualize and discriminate the cellular distribution of tissue antigens using fluorescent immunohistochemical multi-labeling techniques. Although such approaches are routine in non-aging brains, they are not consistently feasible in the aging brain due to the progressive accumulation of autofluorescent pigments, particularly lipofuscin, which strongly excite and emit over a broad spectral range. Consequently, aging research has relied upon colorimetric antibody techniques, where discrimination of tissue antigens is often challenging. We report the application of a simple, reproducible, and affordable protocol using multispectral light-emitting diodes (mLEDs) exposure for the reduction/elimination of lipofuscin autofluorescence (LAF) in aging brain tissue from humans, non-human primates, and mice. The mLEDs lamp has a broad spectral range that spans from the UV to infrared range and includes spectra in the violet/blue and orange/red. After photo quenching, the LAF level was markedly reduced when the tissue background fluorescence before and after mLEDs exposure was compared (p < 0.0001) across the spectral range. LAF elimination was estimated at 95 ± 1%. This approach permitted robust specific fluorescent immunohistochemical co-visualization of commonly studied antigens in aging brains. We also successfully applied this method to specifically visualize CD44 variant expression in aging human cerebral white matter using RNAscope fluorescent in-situ hybridization. Photo quenching provides an attractive means to accelerate progress in aging research by increasing the number of molecules that can be topologically discriminated by fluorescence detection in brain tissue from normative or pathological aging.

A, Upset plot showing the overlap between putamen conserved marker genes of Ast-0, Ast-1 and Ast-2 astrocyte with marker genes of mouse DAA and Gfap-high astrocytes from Habib et al., 2020. B, Violin plots showing the expression level distributions of orthologous genes of murine DAA and Gfap-high astrocyte marker genes in the putamen astrocytes. C, PCA plot using murine DAA and Gfap-high astrocyte marker gene logFC of gene expression (comparing murine DAA and Gfap-high astrocyte with Gfap-low astrocytes, downloaded from Habib et al., 2020) and the logFC of the human orthologous genes (comparing putamen Ast-1 and Ast-2 with Ast-0 astrocytes). D,E, Violin plots showing the expression level distributions of reactive astrocyte marker genes in astrocytes from the (D) putamen and (E) prefrontal cortex. F, Violin plots showing the expression level distributions of A1-, A2-specific activated astrocyte markers and JAK-STAT3 pathway genes. G, Top 10 GO terms in the Biological Process category enriched in the astrocyte subpopulation signature genes (hypergeometric test, FDR-adjusted P value < 0.05, ≥ 5 query genes). Conserved marker genes plotted in panel (B), (D) and (E) were determined by FindConservedMarkers using Wilcoxon Rank Sum test and _metap_ R package with meta-analysis combined P value < 0.05 comparing gene expression in the given cluster with the other cell clusters for AD (n = 4), PD (n = 4) and the controls (n = 4). Genes plotted in (F) were not statistically significantly higher in any of the astrocyte subpopulations.

Aging, a universal process that affects all cells in an organism, is a major risk factor for a group of neuropathies called glaucoma, where elevated intraocular pressure is one of the known stresses affecting the tissue. Our understanding of molecular impact of aging on response to stress in retina is very limited; therefore, we developed a new mouse model to approach this question experimentally. Here we show that susceptibility to response to stress increases with age and is primed on chromatin level. We demonstrate that ocular hypertension activates a stress response that is similar to natural aging and involves activation of inflammation and senescence. We show that multiple instances of pressure elevation cause aging of young retina as measured on transcriptional and DNA methylation level and are accompanied by local histone modification changes. Our data show that repeated stress accelerates appearance of aging features in tissues and suggest chromatin modifications as the key molecular components of aging. Lastly, our work further emphasizes the importance of early diagnosis and prevention as well as age-specific management of age-related diseases, including glaucoma.