Neuronal deletion of the circadian clock gene Bmal1 induces cell-autonomous dopaminergic neurodegeneration
Michael F. Kanan, Patrick W. Sheehan, Jessica N. Haines, Pedro G. Gomez, Adya Dhuler, Collin J. Nadarajah, Zachary M. Wargel, Brittany M. Freeberg, Hemanth R. Nelvagal, Mariko Izumo, Joseph S. Takahashi, Jonathan D. Cooper, Albert A. Davis, Erik S. Musiek
Michael F. Kanan, Patrick W. Sheehan, Jessica N. Haines, Pedro G. Gomez, Adya Dhuler, Collin J. Nadarajah, Zachary M. Wargel, Brittany M. Freeberg, Hemanth R. Nelvagal, Mariko Izumo, Joseph S. Takahashi, Jonathan D. Cooper, Albert A. Davis, Erik S. Musiek
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Research Article Aging Neuroscience

Neuronal deletion of the circadian clock gene Bmal1 induces cell-autonomous dopaminergic neurodegeneration

Abstract

Circadian rhythm dysfunction is a hallmark of Parkinson disease (PD), and diminished expression of the core clock gene Bmal1 has been described in patients with PD. BMAL1 is required for core circadian clock function but also serves nonrhythmic functions. Germline Bmal1 deletion can cause brain oxidative stress and synapse loss in mice, and it can exacerbate dopaminergic neurodegeneration in response to the toxin MPTP. Here we examined the effect of cell type–specific Bmal1 deletion on dopaminergic neuron viability in vivo. We observed that global, postnatal deletion of Bmal1 caused spontaneous loss of tyrosine hydroxylase+ (TH+) dopaminergic neurons in the substantia nigra pars compacta (SNpc). This was not replicated by light-induced disruption of behavioral circadian rhythms and was not induced by astrocyte- or microglia-specific Bmal1 deletion. However, either pan-neuronal or TH neuron–specific Bmal1 deletion caused cell-autonomous loss of TH+ neurons in the SNpc. Bmal1 deletion did not change the percentage of TH neuron loss after α-synuclein fibril injection, though Bmal1-KO mice had fewer TH neurons at baseline. Transcriptomics analysis revealed dysregulation of pathways involved in oxidative phosphorylation and Parkinson disease. These findings demonstrate a cell-autonomous role for BMAL1 in regulating dopaminergic neuronal survival and may have important implications for neuroprotection in PD.

Authors

Michael F. Kanan, Patrick W. Sheehan, Jessica N. Haines, Pedro G. Gomez, Adya Dhuler, Collin J. Nadarajah, Zachary M. Wargel, Brittany M. Freeberg, Hemanth R. Nelvagal, Mariko Izumo, Joseph S. Takahashi, Jonathan D. Cooper, Albert A. Davis, Erik S. Musiek

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Figure 1

Global and brain-specific Bmal1 deletion induces degeneration of dopaminergic neurons in the SNpc.

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Global and brain-specific Bmal1 deletion induces degeneration of dopamin...
(A) Representative images of TH (green) and NeuN (red) staining within the SNpc of Cre–;Bmal1fl/fl control (CAG-Cre–) and CAG-Cre+;Bmal1fl/fl global Bmal1-KO mice (CAG-Cre+). Scale bar: 150 μm. (B) Representative images of TH staining in striatum of CAG-Cre– and Cre+ mice. Scale bar: 200 μm. (C) Stereological counts of TH+ cells in the SNpc of CAG-Cre– controls and CAG-Cre+ Bmal1-KO mice. n = 5–6 mice per genotype. Fold change normalized to average of Cre– condition. (D) Quantification of striatal TH immunoreactivity (IR) intensity from images in B. Fold change normalized to average of Cre– condition. (E) Quantification of NeuN IR (% area) in the SNpc of CAG-Cre– controls and CAG-Cre+ Bmal1-KO mice. n = 6 mice per genotype. Fold change normalized to average of Cre– condition. (F) Representative images of SNpc TH staining (brown) with H&E counterstaining (purple) in the SNpc of Nestin-Cre–;Bmal1fl/fl control and Nestin-Cre+;Bmal1fl/fl brain-specific Bmal1-KO mice. Scale bar: 150 μm. (G) Representative images of TH staining in striatum of Nestin-Cre– and Cre+ mice. Scale bar: 200 μm. (H) Stereological counts of TH+ cells in the SNpc and Nestin-Cre– control (Cre–) and Nestin-Cre+ brain-specific Bmal1-KO mice (Cre+). n = 5 mice per genotype. (I) Striatal TH IR intensity quantified from images in G. For C–E, H, and I, each circle represents averaged counts from a single mouse, and fold change was normalized to average of Cre– condition. In all panels, data represent mean ± SEM. *P < 0.05, **P < 0.01 by 2-tailed t test.