Transgenic neuronal overexpression reveals that stringently regulated p23 expression is critical for coordinated movement in mice

Abstract

Backgroundp23 belongs to the highly conserved p24 family of type I transmembrane proteins, which participate in the bidirectional protein transport between the endoplasmic reticulum and Golgi apparatus. Mammalian p23 has been shown to interact with γ-secretase complex, and modulate secretory trafficking as well as intramembranous processing of amyloid precursor protein in cultured cells. Negative modulation of β-amyloid production by p23 in cultured cell lines suggested that elevation of p23 expression in neurons might mitigate cerebral amyloid burden.ResultsWe generated several lines of transgenic mice expressing human p23 in neurons under the control of Thy-1.2 promoter. We found that even a 50% increase in p23 levels in the central nervous system of mice causes post-natal growth retardation, severe neurological problems characterized by tremors, seizure, ataxia, and uncoordinated movements, and premature death. The severity of the phenotype closely correlated with the level of p23 overexpression in multiple transgenic lines. While the number and general morphology of neurons in Hup23 mice appeared to be normal throughout the brain, abnormal non-Golgi p23 localization was observed in a subset of neurons with high transgene expression in brainstem. Moreover, detailed immunofluorescence analysis revealed marked proliferation of astrocytes, activation of microglia, and thinning of myelinated bundles in brainstem of Hup23 mice.ConclusionsThese results demonstrate that proper level of p23 expression is critical for neuronal function, and perturbing p23 function by overexpression initiates a cascade of cellular reactions in brainstem that leads to severe motor deficits and other neurological problems, which culminate in premature death. The neurological phenotype observed in Hup23 mice highlights significant adverse effects associated with manipulating neuronal expression of p23, a previously described negative modulator of γ-secretase activity and β-amyloid production. Moreover, our report has broader relevance to molecular mechanisms in several neurodegenerative diseases as it highlights the inherent vulnerability of the early secretory pathway mechanisms that ensure proteostasis in neurons.

A Function for EHD Family Proteins in Unidirectional Retrograde Dendritic Transport of BACE1 and Alzheimer’s Disease Aβ Production

“…The antibodies and methods used for staining human and mouse brain tissue are described under Supplemental Experimental Procedures (Zhao et al, 2007; Gong et al, 2011). …”

Characterization of brain cell nuclei with decondensed chromatin

“…These results are supported by previous studies showing that although NeuN expression varies widely among neurons in different regions of the brain, histone deacetylases are in general most strongly expressed in regions rich in neuronal nuclei. For example, NeuN nuclear protein staining levels are reported to be at the highest in layers of neurons within the cortex and the layer of pyramidal neurons in the hippocampus (regions CA1-4 and dentate gyrus) and distinct, but weaker, throughout the granule cell layer of the cerebellum and in the pontine nucleus of the brain stem (Mullen et al, 1992;Weyer and Schilling, 2003;Gong et al, 2011). Based on in situ RNA hybridization experiments, the non-sirtuin histone lysine deacetylases HDAC2, HDAC3, HDAC4, HDAC5, and HDAC11 and the sirtuin deacetylase SIRT1 are highly expressed in neurons in the cortex and hippocampal regions and with few exceptions more weakly expressed in other cell types in the brain (Broide et al, 2007, Huang et al, 2011.…”

Ca2+ Influx through Store-operated Ca2+ Channels Reduces Alzheimer Disease β-Amyloid Peptide Secretion

“…The membranes were sequentially incubated with primary antibodies and horseradish peroxidase-conjugated protein A (Sigma) or goat anti-mouse IgG (Jackson ImmunoResearch Laboratories), and signals were visualized by enhanced chemiluminescence detection (PerkinElmer Life Sciences). Alternatively, the blots were incubated with IR-dye-conjugated secondary antibodies and visualized by the Odyssey infrared imaging system (LI-COR Biosciences) as described (39).…”