Sertraline slows disease progression and increases neurogenesis in N171-82Q mouse model of Huntington's disease

Abstract

Huntington's disease (HD) is an inherited progressive neurodegenerative disorder resulting from CAG repeat expansion in the gene that encodes for the protein huntingtin. To identify neuroprotective compound (s) that can slow down disease progression and can be administered long term with few side effects in Huntington's disease, we investigated the effect of sertraline, a selective serotonin reuptake inhibitor (SSRI) which has been shown to upregulate BDNF levels in rodent brains. We report here that in HD mice sertraline increased BDNF levels, preserved chaperone protein HSP70 and Bcl-2 levels in brains, attenuated the progression of brain atrophy and behavioral abnormalities and thereby increased survival. Sertraline also enhanced neurogenesis, which appeared to be responsible for mediating the beneficial effects of sertraline in HD mice. Additionally, the effective levels of sertraline are comparable to the safe levels achievable in humans. The findings suggest that sertraline is a potential candidate for treatment of HD patients.

Figure 1

Sertraline increases survival and improves motor behavioral performance, but does not affect body weight loss in HD mice. Twelve-week-old male HD mice were administered sertraline daily at doses of 5, 10, and 20 mg/kg or vehicle (0.2% tween -80) until the end of study. (a) Survival of HD mice was significantly extended by sertraline treatment in a dose-dependent manner. The p values are 0.041 between vehicle and sertraline 5 mg/kg groups, 0.039 between vehicle and sertraline 10 mg/kg groups, and 0.012 between vehicle and sertraline 20 mg/kg groups by Kaplan-Meier analysis. (b) There was no significant difference in body weight loss by sertraline treatment. (c and d) Motor behavioral performance was evaluated by an accelerating rotarod apparatus in 16-(c) and 18-(d) week-old mice, n=8–15. The values are the mean and SE. *p<0.05, compared to the value of nontransgenic-control group; **p<0.05 compared to the values of HD-vehicle group by Standard student t-tests.

Figure 2

Sertraline reduces brain atrophy but not huntingtin inclusions in N171-82Q HD mice. (a) Representative photomicrographs of brain sections of HD mice and nontransgenic mice (nontg), scale bar=120 μm. (b) Quantification of striatal volume and (c) cerebral lateral ventricle volume. Data are presented as mean and SE, n= 4 mice in each group. *p<0.05, compared to the value of nontg control group; **p<0.05 compared to the value of HD-vehicle group by Standard Student t-tests. (d) Representative micrographs of htt inclusions immunostained by EM48 antibody in HD mice treated with sertraline or vehicle. Scale bar =20 μm.

Figure 3

Sertraline normalizes BDNF protein levels and serotonin (5-HT) levels, and upregulates HSP70 and Bcl-2 levels. Twelve-week-old mice were administered sertraline at 10 mg/kg. Mice were euthanized 4 weeks after sertraline administration, (a) BDNF protein levels were measured in cortical tissue by ELISA. (b) Serotonin levels were measured by HPLC method in striatum. The values are the mean and SE, n=6. *p<0.05, compared to the values of nontg control group, **p<0.05 compared to the values of HD-control group by Standard Student t-tests. (c and d). HSP70 protein levels and Bcl-2 levels were measured in striatal tissues by Western blot analysis, the top panels are representative blots, and the bottom panel is the quantification data (mean and SE) from three mice in each group, *p<0.05 compared to the values of nontg-vehicle group; **p<0.05 compared the values of HD-vehicle group by Standard Student t-tests.

Figure 4

Sertraline increases neurogenesis in subgranular zone (SGZ) of dentate gyrus in HD mice and control mice. (a) Sertraline (10 mg/kg) was administered to mice at 12 weeks of age for 4 weeks. Mice then received 5-bromo-2-deoxyuridine (BrdU) and were perfused at 3 days after the last BrdU injection for cell proliferation, Scale bar = 100 μm. (b) mice were perfused 3 weeks after the last BrdU injection for quantifying survival of newly generated cells. (c) representative sections were double labeled with anti-BrdU and anti-NeuN antibody (neuronal marker) or anti-GFAP antibody (astrocyte marker) to identify the phenotypes of newly generated cells. Representative images from confocal microscope, green shows BrdU-positive staining and red shows NeuN- or GFAP-positive staining. Scale bar = 20 μm. (d) Quantification of newly generated neurons in dentate gyrus. All values are the mean and SE. n=4 mice per group. *p<0.05, compared to the values of nontg-vehicle group, **p<0.05 compared to the values of HD vehicle group by standard student t-tests.

Figure 4

Sertraline increases neurogenesis in subgranular zone (SGZ) of dentate gyrus in HD mice and control mice. (a) Sertraline (10 mg/kg) was administered to mice at 12 weeks of age for 4 weeks. Mice then received 5-bromo-2-deoxyuridine (BrdU) and were perfused at 3 days after the last BrdU injection for cell proliferation, Scale bar = 100 μm. (b) mice were perfused 3 weeks after the last BrdU injection for quantifying survival of newly generated cells. (c) representative sections were double labeled with anti-BrdU and anti-NeuN antibody (neuronal marker) or anti-GFAP antibody (astrocyte marker) to identify the phenotypes of newly generated cells. Representative images from confocal microscope, green shows BrdU-positive staining and red shows NeuN- or GFAP-positive staining. Scale bar = 20 μm. (d) Quantification of newly generated neurons in dentate gyrus. All values are the mean and SE. n=4 mice per group. *p<0.05, compared to the values of nontg-vehicle group, **p<0.05 compared to the values of HD vehicle group by standard student t-tests.

Figure 5

Sertraline increases neurogenesis in subventricular zone (SVZ) of mice. Mice were administered sertraline at 10 mg/kg from 12 weeks of age for 4 weeks. Mice were perfused at 3 days after the last BrdU injection for cell proliferation study indicating BrdU-positive cells in SVZ (a) and 3 weeks after the last injection for quantifying survival of newly generated cells indicated by remaining BrdU-positive cells (b). All values are the mean and SE. n=4 mice per group. *p<0.05, compared to the values of nontg vehicle group, **p<0.05 compared to the values of HD vehicle group by standard student t-tests.

Figure 6

Neurogenesis induced by sertraline is required for its survival extension effect and improvement of motor performance in HD mice. (a) Radiographic alignment of the mouse brain with 8 ×10 mm radiation treatment port (left) and corresponding structures (right). The stereotactic head holder is visible in the radiograph as bars on either side of the head. Structures in the right panel are the right and left lateral ventricles (green, red) and dentate gyrus of hippocampus (purple, blue) from the atlas of Paxions and Franklin (2001). (b) There was significant reduction of cell proliferation in both SVZ and SGZ by X-ray irradiation, which was not rescued by sertraline treatment. The values are mean and SE from four HD mice in each group. *p<0.05 compared to the values of sham-vehicle group by standard student t-tests. (c) X-ray irradiation abolished the improved motor performance by sertraline in HD mice. Data are presented as mean and SE from 10 mice in each group. *p<0.05 compared to the values of HD-sham group, ^#p<0.05 compared to the values of HD-sham-sertraline group by standard student t-tests. (d) The survival extension effect of sertraline was partially eliminated by X-ray irradiation. Survival was analyzed by Kaplan-Meier analysis. The p value between sham group and sham+ser group is 0.00125; the p value between X-ray+ser group and sham+ser group is 0.0248.