Vascular and neurogenic rejuvenation of the aging mouse brain by young systemic factors

Abstract

In the adult central nervous system, the vasculature of the neurogenic niche regulates neural stem cell behavior by providing circulating and secreted factors. Age-related decline of neurogenesis and cognitive function is associated with reduced blood flow and decreased numbers of neural stem cells. Therefore, restoring the functionality of the niche should counteract some of the negative effects of aging. We show that factors found in young blood induce vascular remodeling, culminating in increased neurogenesis and improved olfactory discrimination in aging mice. Further, we show that GDF11 alone can improve the cerebral vasculature and enhance neurogenesis. The identification of factors that slow the age-dependent deterioration of the neurogenic niche in mice may constitute the basis for new methods of treating age-related neurodegenerative and neurovascular diseases.

Fig. 1. Rejuvenation of progenitor cells by heterochronic parabiosis

(A-C) Confocal images showing the effects of parabiosis on proliferative (A), neural stem (B) and progenitor cells (C) in the SVZ of isochronic and heterochronic mice. Scale bar: 50μm. (D-E) Quantification of neural stem (D) and progenitor cell (E) populations of the above images (n=9 animals for each experimental group, *p<0.05, **p<0.01, ***p<0.001). Data shown as mean±S.E.M; statistical analysis by ANOVA.

Fig. 2. Heterochronic parabiosis enhances neurogenesis and cognitive functions in the aging mouse

(A) Representative images of olfactory bulbs showing newborn neurons in isochronic and heterochronic parabionts. Scale bar: 100μm. Circles in higher magnification inserts indicate BrdU⁺/NeuN⁺ double-positive cells. (B, C) Quantification of neurogenesis in the olfactory bulbs of old (B) and young (C) parabionts. (n=4, *p<0.05). (D) Measurement of the exploratory time during the olfactory sensitivity assay (n=3). Data shown as mean±S.E.M; statistical analysis by t-test. “n=” indicates the number of animals for each experimental group.

Fig. 3. Young blood induces vascular remodeling and increases blood flow in old mice

(A) Confocal images of the SVZ area showing the changes in vasculature after heterochronic parabiosis. Scale bar: 50μm. (B) Measurement of blood vessel volume in isochronic and heterochronic parabionts (n_old= 9, n_young=6). (C, D) Measurements of cerebral blood flow in the SVZ region of the parabionts: Iso-O versus Iso-Y (C) or Het-O (D) mice (n=4). (E) Perfusion MRI images of the brain. “V” indicates the ventricles. Data shown as mean±S.E.M; statistical analysis by ANOVA in (B) and t-test in (C,D); *p<0.05, **p<0.01, ***p<0.001. “n=” indicates the number of animals for each experimental group.

Fig. 4. GDF11 enhances vascular remodeling and neurogenesis

(A, B) Confocal images of coronal SVZ sections showing that 22-month old mice injected with rGDF11 for 4 weeks have enhanced vascularization (A) as well as increased Sox2⁺ neural stem cell populations (B) compared to control. (C) Measurement of blood vessel volume in rGDF11-treated and control mice (n=9). (D) Quantification of Sox2⁺ cells in the SVZ area (n=6); “n=” indicates the number of animals for each experimental group. (E, F) Quantification (E) and representative images (F) of the percentage of phospho-SMAD2/3⁺ cells in primary brain capillary endothelial cell cultures treated with either GDF11 (40ng/ml) or TFG-β (10ng/ml) in the presence of sodium orthovanadate used to inhibit phosphatase activity for 30 minutes (n=7). Scale bar: 100 μm. Data shown as mean±S.E.M; statistical analysis by t-test, between each experimental condition and the untreated control, *p<0.05, **p<0.01, ***p<0.001.