. SNPs associated with cerebrospinal fluid phospho-tau levels influence rate of decline in Alzheimer's disease. PLoS Genet. 2010 Sep;6(9) PubMed.

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  1. This is a very interesting paper from Allison Goate and coworkers, who push genotype-phenotype analyses to the next level—towards understanding how variations in biomarkers relate to risk of progression of disease. A specific allele of calcineurin B, one of the subunits of calcineurin, is associated with rate of progression, phospho-tau levels, and tangle numbers. This is a tour de force of genotype-phenotype correlations and begins to potentially explore the wide variability in disease progression observed clinically. Of importance, age of onset travels not with calcineurin B, but with amyloid-related markers.

    Calcineurin activation has been implicated by Paul Greengard and colleagues, Roberto Malinow’s laboratory, as well as multiple others, as being critical for expression of amyloid-β synaptotoxicity. Recent data from our laboratory, and from Chris Norris and colleagues, demonstrated elevated calcineurin activity in neurons and in glia in AD models and in AD brain, in part due to post-translational changes that lead to a constitutively active form. How this relates to the new genetic findings, and to tau phosphorylation, is not yet clear—and raises new questions about how regulation of calcineurin at the mRNA level relates to activity in the AD brain. Nonetheless, the link of biochemical and genetic data both focusing on calcineurin pathways is intriguing, and serves to highlight the potential importance of this central signaling pathway in AD pathophysiology.

  2. This elegant manuscript by Cruchaga et al. reveals that CSF phospho-tau levels and the rate of disease progression in AD subjects are strongly correlated to the presence of SNPs in the regulatory B subunit of calcineurin, a Ca2+/calmodulin-dependent protein phosphatase implicated in several peripheral and neurologic disorders. These important observations could help establish a novel diagnostic marker in the clinic and lead to the development of treatments tailored to specific patient subpopulations.

    At the same time, caution may be warranted in regard to the functional impact of these SNPs on calcineurin function in AD. The authors suggest that calcineurin B SNPs “reduce calcineurin expression/activity leading to an increase in tau phosphorylation, tau pathology and neurodegeneration in individuals with Aβ deposition.” This conclusion was based on two primary pieces of evidence: First, that calcineurin inhibitors increase tau phosphorylation in mice (1,3) and second, that calcineurin activity is reduced in Alzheimer’s disease brain (4). However, numerous recent findings seem inconsistent with a “reduced calcineurin” hypothesis. In particular, calcineurin inhibitors (or inhibitors of the calcineurin-dependent transcription factor NFAT) typically provide strong protection against synaptic dysfunction (5,6), dendritic atrophy/spine retraction (7-9), neuroinflammation (10,11), amyloid pathology (12,13), neuronal death (14,15), and cognitive decline (16) in a variety of cell culture and/or animal models of AD.

    Moreover, recent studies using alternative antibodies and assays have observed hyperactive, rather than hypoactive, calcineurin signaling in AD mice and in subjects with MCI or AD (8,16-19). The work performed on postmortem human tissue suggests that AD-mediated changes in calcineurin signaling are very complex and depend on a number of factors including: the brain region, cell type (neurons vs glia), and calcineurin isoform (alpha vs beta) investigated; the proteolytic state and subcellular localization of the calcineurin catalytic subunit (i.e. the A subunit); and the pathologic and cognitive status of the subject. Clearly, it will be important to determine how SNPs in the regulatory calcineurin B subunit affect these calcineurin A signaling properties.

    References:

    . Inhibition of calcineurin by infusion of CsA causes hyperphosphorylation of tau and is accompanied by abnormal behavior in mice. Biol Chem. 2006 Jul;387(7):977-83. PubMed.

    . Infusion of FK506, a specific inhibitor of calcineurin, induces potent tau hyperphosphorylation in mouse brain. Brain Res Bull. 2008 Jul 30;76(5):464-8. PubMed.

    . Reduction of calcineurin activity in brain by antisense oligonucleotides leads to persistent phosphorylation of tau protein at Thr181 and Thr231. Mol Pharmacol. 1999 Apr;55(4):632-41. PubMed.

    . Reduction of calcineurin enzymatic activity in Alzheimer's disease: correlation with neuropathologic changes. J Neuropathol Exp Neurol. 1996 Aug;55(8):924-31. PubMed.

    . Soluble oligomers of amyloid Beta protein facilitate hippocampal long-term depression by disrupting neuronal glutamate uptake. Neuron. 2009 Jun 25;62(6):788-801. PubMed.

    . Alzheimer amyloid beta-peptide inhibits the late phase of long-term potentiation through calcineurin-dependent mechanisms in the hippocampal dentate gyrus. Neurobiol Learn Mem. 2002 May;77(3):354-71. PubMed.

    . Natural oligomers of the Alzheimer amyloid-beta protein induce reversible synapse loss by modulating an NMDA-type glutamate receptor-dependent signaling pathway. J Neurosci. 2007 Mar 14;27(11):2866-75. PubMed.

    . Amyloid beta induces the morphological neurodegenerative triad of spine loss, dendritic simplification, and neuritic dystrophies through calcineurin activation. J Neurosci. 2010 Feb 17;30(7):2636-49. PubMed.

    . Abeta plaques lead to aberrant regulation of calcium homeostasis in vivo resulting in structural and functional disruption of neuronal networks. Neuron. 2008 Jul 31;59(2):214-25. PubMed.

    . Interleukin-1beta-dependent signaling between astrocytes and neurons depends critically on astrocytic calcineurin/NFAT activity. J Biol Chem. 2008 Aug 8;283(32) Epub 2008 Jun 9 PubMed.

    . Synapse loss and microglial activation precede tangles in a P301S tauopathy mouse model. Neuron. 2007 Feb 1;53(3):337-51. PubMed.

    . Disrupted intracellular calcium regulates BACE1 gene expression via nuclear factor of activated T cells 1 (NFAT 1) signaling. Aging Cell. 2008 Mar;7(2):137-47. PubMed.

    . RAGE regulates BACE1 and Abeta generation via NFAT1 activation in Alzheimer's disease animal model. FASEB J. 2009 Aug;23(8):2639-49. PubMed.

    . Overactivation of calcineurin induced by amyloid-beta and prion proteins. Neurochem Int. 2008 May;52(6):1226-33. PubMed.

    . Selective induction of calcineurin activity and signaling by oligomeric amyloid beta. Aging Cell. 2008 Dec;7(6):824-35. PubMed.

    . Acute inhibition of calcineurin restores associative learning and memory in Tg2576 APP transgenic mice. Neurobiol Learn Mem. 2007 Sep;88(2):217-24. PubMed.

    . Cognitive decline in Alzheimer's disease is associated with selective changes in calcineurin/NFAT signaling. J Neurosci. 2009 Oct 14;29(41):12957-69. PubMed.

    . Truncation and activation of calcineurin A by calpain I in Alzheimer disease brain. J Biol Chem. 2005 Nov 11;280(45):37755-62. PubMed.

    . Calcineurin triggers reactive/inflammatory processes in astrocytes and is upregulated in aging and Alzheimer's models. J Neurosci. 2005 May 4;25(18):4649-58. PubMed.

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