Circadian clock proteins regulate neuronal redox homeostasis and neurodegeneration
Erik S. Musiek, … , David M. Holtzman, Garret A. FitzGerald
Erik S. Musiek, … , David M. Holtzman, Garret A. FitzGerald
Published November 25, 2013
Citation Information: J Clin Invest. 2013;123(12):5389-5400. https://doi.org/10.1172/JCI70317.
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Research Article

Circadian clock proteins regulate neuronal redox homeostasis and neurodegeneration

Abstract

Brain aging is associated with diminished circadian clock output and decreased expression of the core clock proteins, which regulate many aspects of cellular biochemistry and metabolism. The genes encoding clock proteins are expressed throughout the brain, though it is unknown whether these proteins modulate brain homeostasis. We observed that deletion of circadian clock transcriptional activators aryl hydrocarbon receptor nuclear translocator–like (Bmal1) alone, or circadian locomotor output cycles kaput (Clock) in combination with neuronal PAS domain protein 2 (Npas2), induced severe age-dependent astrogliosis in the cortex and hippocampus. Mice lacking the clock gene repressors period circadian clock 1 (Per1) and period circadian clock 2 (Per2) had no observed astrogliosis. Bmal1 deletion caused the degeneration of synaptic terminals and impaired cortical functional connectivity, as well as neuronal oxidative damage and impaired expression of several redox defense genes. Targeted deletion of Bmal1 in neurons and glia caused similar neuropathology, despite the retention of intact circadian behavioral and sleep-wake rhythms. Reduction of Bmal1 expression promoted neuronal death in primary cultures and in mice treated with a chemical inducer of oxidative injury and striatal neurodegeneration. Our findings indicate that BMAL1 in a complex with CLOCK or NPAS2 regulates cerebral redox homeostasis and connects impaired clock gene function to neurodegeneration.

Authors

Erik S. Musiek, Miranda M. Lim, Guangrui Yang, Adam Q. Bauer, Laura Qi, Yool Lee, Jee Hoon Roh, Xilma Ortiz-Gonzalez, Joshua T. Dearborn, Joseph P. Culver, Erik D. Herzog, John B. Hogenesch, David F. Wozniak, Krikor Dikranian, Benoit I. Giasson, David R. Weaver, David M. Holtzman, Garret A. FitzGerald

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Figure 1

Marked age-dependent cerebral astroglial activation in Bmal1 KO mice.

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Marked age-dependent cerebral astroglial activation in Bmal1 KO mice. ...
GFAP staining of sections from 6-month-old WT (A) and Bmal1 KO (B) mice shows severe astrogliosis throughout the brain of KO mice and most severe in cortex. Scale bars: 200 μm. (C) GFAP staining of retrosplenial cortex sections from WT and KO mice at 2 weeks of age (0.5 months), 2.5 months, and 6 months of age demonstrates age-dependent astrogliosis, which is present by age 2.5 months. Scale bar: 100 μm (D) Quantification of Gfap mRNA by qPCR and GFAP immunoreaction (IR; % area) by immunostaining of cortex samples shows age-dependent increases in astrogliosis. qPCR was normalized to 18S mRNA levels and is expressed as fold change compared with 2.5-month-old WT control mice. Black circles represent WT mice, and gray triangles represent KO mice (n = 3 mice/point). *P < 0.05 by 1-way ANOVA versus 2-week-old WT mice. (E) Region-specific astrocyte activation in Bmal1 KO brain. Ten mice per genotype were stained for GFAP, while 3 mice per genotype were quantified. Cing, cingulate cortex; Piri, piriform cortex; Sens, sensory cortex; Rs, retrosplenial cortex; Hipp, hippocampus; Str, striatum; Sept, septum; Thal, thalamus. (F) Increased COX2 protein (F and G) and Ptghs2 mRNA (G) in 6-month-old Bmal1 KO cortex. (H) Increased Tnfa mRNA by qPCR in Bmal1 KO cortex. n = 4 mice/genotype (G and H). *P < 0.05 versus WT by 2-way ANOVA with Bonferroni’s post test.