Nigrostriatal alterations in bone morphogenetic protein receptor II dominant negative mice

Abstract

Background: We previously demonstrated that exogenous application of bone morphogenetic protein 7 (BMP7) reduced 6-hydroxydopamine-mediated neurodegeneration in a rodent model of Parkinson's disease. The purpose of this study is to examine the endogenous neurotrophic properties of BMP Receptor II in dopaminergic neurons of the nigrostriatal pathway.

Methods: Adult male BMPRII dominant negative (BMPRIIDN) mice and their wild type controls (WT) were placed in the activity chambers for 3 days to monitor locomotor activity. Animals were sacrificed for tyrosine hydroxylase (TH) immunostaining. A subgroup of BMPRIIDN and WT mice were injected with high doses of methamphetamine (MA) and were sacrificed for terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) histochemistry at 4 days after injection.

Results: BMPRIIDN mice had lower locomotor activity than the WT. There is a significant decrease in TH neuronal number in substantia nigra compacta, TH fiber density in the substantia nigra reticulata, and TH immunoreactivity in striatum in the BMPRIIDN mice, suggesting that deficiency in endogenous BMP signaling reduces dopaminergic innervation and motor function in the nigrostriatal pathway. Administration of MA increased TUNEL labeling in the substantia nigra in the BMPRIIDN mice.

Conclusions: Endogenous BMPs have trophic effects on nigrostriatal dopaminergic neurons. Deficiency in BMP signaling increases vulnerability to insults induced by high doses of MA.

Fig. 1

Locomotor activity of BMPRIIDN and WT mice. Animals were individually placed in the activity chambers for 3 days. Ten different locomotor parameters were recorded daily. BMPRIIDN mice (dashed tracing) had a significant decrease in horizontal (total distance traveled, movement time, horizontal activity, number of movement, p<0.01, two-way ANOVA), vertical movement (vertical activity, vertical time, number of vertical movement, p<0.05, two-way ANOVA), and stereotypy (stereotype time, # of stereotypy, stereotypy counts, p<0.05, two-way ANOVA) than the wild type mice (solid tracing)

Fig. 2

BMPRIIDN mice exhibit decreased TH-immunoreactivity in nigra and striatum. Photomicrographs were taken from WT and BMPRIIDN mice. THir is reduced in striatum (WT: A1 vs. BMPRIIDN: A2), VTA (WT: B1 vs. BMPRIIDN: B2), SNpc (WT: C1 vs. BMPRIIDN: C2) in the BMPRIIDN mouse. Less THir fibers were also found in the SNpr in this animal (WT: D1 vs. BMPRIIDN: D2). Calibration: A: 2000 μm; B: 500 μm; C, D: 250 μm. (E) TH immunoreactivity is reduced in BMPRIIDN mice. Averaged THir was taken from 5 WT (clear bar) and 5 BMPRIIDN (dark bar) mice. THir and TH neuronal density were normalized by comparison to the mean of WT controls. In all regions, BMPRIIDN mice had significantly less THir than the WT (*p<0.05, t-test)

Fig. 3

High doses of MA altered TUNEL and THir in nigrostriatal pathway. BMPRIIDN (A1) and WT (A2) mice were sacrificed on the 4th day after MA administration (10 mg/kg, ×4). MA injection induced TUNEL labeling. There is an enhancement of TUNEL activity in SNpc (−3.64 mm to bregma) in the BMPRIIDN (A1), compared to the WT (A2). Calibration: 50 μm. (B) The optical density of TUNEL labeling was averaged in 2 regions in SNpc (AP to bregma: −3.64 and −3.80 mm). MA injection significantly increased TUNEL density in the BMPRIIDN mice (p< 0.05, 2-way ANOVA). (C1–C3) THir in nigra and striatum after MA injection in BMPRIIDN and WT mice. THir was examined at 4^th day after MA injection. MA significantly reduced THir in striatum and SNpr in the WT mice. There is no difference in THir in striatum and nigra with and without MA treatment in the BMPRIIDN mice (*p<0.05, 1-way ANOVA)