25-Hydroxyvitamin D Depletion Does Not Exacerbate MPTP-Induced Dopamine Neuron Damage in Mice

Recent clinical evidence supports a link between 25-hydroxyvitamin D insufficiency (serum 25-hydroxyvitamin D [25(OH)D] levels <30 ng/mL) and Parkinson’s disease. To investigate the effect of 25(OH)D depletion on neuronal susceptibility to toxic insult, we induced a state of 25(OH)D deficiency in mice and then challenged them with the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We found there was no significant difference between control and 25(OH)D-deficient animals in striatal dopamine levels or dopamine transporter and tyrosine hydroxylase expression after lesioning with MPTP. Additionally, we found no difference in tyrosine hydroxylase expression in the substantia nigra pars compacta. Our data suggest that reducing 25(OH)D serum levels in mice has no effect on the vulnerability of nigral dopaminergic neurons in vivo in this model system of parkinsonism

Serum 25(OH)D levels are not changed in VMAT2 LO mice.

<p>Serum 25(OH)D levels were measured in both young (2–3 month old) and old (12–15 month) VMAT2 WT and LO mice to determine loss of dopamine has any effect on 25(OH)D serum levels No differences were observed between WT and LO mice; however, older mice have higher serum 25-hydroxyvitamin D levels than young mice (***, p<0.0001).</p

MPTP lesioning does not affect serum 25(OH)D levels.

<p>After MPTP lesion, serum 25(OH)D levels were measured to determine if MPTP lesion had any effect (Control/Saline Group- 40.40±1.1 ng/ml; Control/MPTP Group- 40.60±1.1 ng/ml; Vitamin D Depletion/Saline Group- 6.60±0.7 ng/ml; Vitamin D Depletion/MPTP Group- 5.91±1.4 ng/ml; n = 4 (***, p<0.0001).</p

25(OH)D depletion does not exacerbate loss of tyrosine hydroxylase staining in the striatum and nigra after MPTP lesion.

<p>A) Representative TH staining of the striatum. B) Representative TH staining of the nigra.</p

MPP+ levels are not altered by 25(OH)D depletion.

<p>Mice were fed vitamin D depleted chow for 50 days and given a single dose of MPTP (20 mg/kg). MPP+ levels were measured by HPLC.</p

Effects of 25(OH)D depletion on TH and DAT expression in MPTP-lesioned mice.

<p>A) Western analyses of striatal TH and DAT levels after MPTP lesion in vitamin D depletion mice. A representative blot is shown. β-tubulin is shown as a loading control. B,C) Densitometric analyses of striatal TH and DAT are shown (Relative values ± SEM; n = 4, ***p<0.001), respectively.</p

Schematic of experimental design to deplete mice of 25(OH)D levels and challenge with MPTP.

<p>On day 1, mice were weighed and randomly assigned to either a group receiving vitamin D depleted chow or a group receiving control chow supplemented with vitamin D. Mice were weighed weekly to check for changes in body mass. After 36 days, 25(OH)D depletion was confirmed by ELISA assay. Then, mice were trained daily to learn the forepaw stride length task from days 44–48. On day 49, baseline behavior was measured. On day 50, MPTP injections began. Mice received a daily injection of either PBS or 15 mg/kg MPTP for 4 days. The mice were allowed to recover for 7 days. On day 60, post-MPTP behavior was measured prior to sacrificing the mice.</p