Arc/Arg3.1 regulates an endosomal pathway essential for activity-dependent ß-amyloid generation.

Assemblies of ß-amyloid (Aß) peptides are pathological mediators of Alzheimer's Disease (AD) and are produced by the sequential cleavages of amyloid precursor protein (APP) by ß-secretase (BACE1) and γ-secretase. The generation of Aß is coupled to neuronal activity, but the molecular basis is unknown. Here, we report that the immediate early gene Arc is required for activity-dependent generation of Aß. Arc is a postsynaptic protein that recruits endophilin2/3 and dynamin to early/recycling endosomes that traffic AMPA receptors to reduce synaptic strength in both hebbian and non-hebbian forms of plasticity. The Arc-endosome also traffics APP and BACE1, and Arc physically associates with presenilin1 (PS1) to regulate γ-secretase trafficking and confer activity dependence. Genetic deletion of Arc reduces Aß load in a transgenic mouse model of AD. In concert with the finding that patients with AD can express anomalously high levels of Arc, we hypothesize that Arc participates in the pathogenesis of AD.

Novel role of neuronal Ca2+ sensor-1 as a survival factor up-regulated in injured neurons.

A molecular basis of survival from neuronal injury is essential for the development of therapeutic strategy to remedy neurodegenerative disorders. In this study, we demonstrate that an EF-hand Ca2+-binding protein neuronal Ca2+ sensor-1 (NCS-1), one of the key proteins for various neuronal functions, also acts as an important survival factor. Overexpression of NCS-1 rendered cultured neurons more tolerant to cell death caused by several kinds of stressors, whereas the dominant-negative mutant (E120Q) accelerated it. In addition, NCS-1 proteins increased upon treatment with glial cell line-derived neurotrophic factor (GDNF) and mediated GDNF survival signal in an Akt (but not MAPK)-dependent manner. Furthermore, NCS-1 is significantly up-regulated in response to axotomy-induced injury in the dorsal motor nucleus of the vagus neurons of adult rats in vivo, and adenoviral overexpression of E120Q resulted in a significant loss of surviving neurons, suggesting that NCS-1 is involved in an antiapoptotic mechanism in adult motor neurons. We propose that NCS-1 is a novel survival-promoting factor up-regulated in injured neurons that mediates the GDNF survival signal via the phosphatidylinositol 3-kinase-Akt pathway.

Regulation of the neuronal fate by DeltaFosB and its downstream target, galectin-1.

In mammals, the regulation of the cell fate to either proliferate, differentiate, arrest cell growth, or initiate programmed cell death is the most fundamental mechanism for maintaining normal cell function and tissue homeostasis. Under multiple signaling pathways, Jun and Fos family proteins are known to play important roles as components of an AP-1 (activator protein-1) complex, to regulate the transcription of various genes involved in cell proliferation, differentiation and programmed cell death. DeltaFosB, one of the AP-1 subunits encoded by alternatively spliced fosB mRNA, triggers one round of proliferation in quiescent rat embryo cell lines, followed by a different cell fate such as morphological alteration or delayed cell death. As one of the downstream targets of the DeltaFosB in rat3Y1 cell line, we identified rat galectin-1 and its novel variant, galectin-1beta, and demonstrated that the expression of galectin-1 is required for the proliferative activation of quiescent rat1A cells by DeltaFosB, thus indicating that galectin-1 is one of functional targets of DeltaFosB. The expression of DeltaFosB is highly inducible in the adult brain in response to various insults such as ischemic reperfusion injury, seizure induced by electric stimulation or cocaine administration. On the other hand, galectin-1 has also been shown to be involved in the regeneration of damaged axons in the peripheral nerve, as well as in neurite outgrowth or synaptic connectivity in the olfactory system during development. We herein propose that DeltaFosB together with galectin-1, may therefore mediate neuroprotection and neurogenesis in response to brain damage.

[A case of brain ischemia presenting spectacular shrinking deficit in adult-onset Still's disease associated with antiphospholipid antibody syndrome].

A 63-year-old man presenting remittent fever and multiple arthralgia was diagnosed as adult-onset Still's disease (AOSD), and started with prednisolone treatment. However, he suddenly developed loss of consciousness, paresis of the right upper extremity and aphasia shortly after the treatment. We detected an increased signal of brain tissue lactate at the branch territory of left middle cerebral artery by MR spectroscopy (MRS), but no lesions by diffusion-weighted nor T2-weighted MRI, suggesting acute brain ischemia of embolic mechanism. Most of the symptoms resolved in a couple of hours after the onset, showing spectacular shrinking deficit (SSD). The patient also revealed complication of antiphospholipid antibody syndrome (APS), which may be associated with ischemic event. This is the first case of acute brain ischemia with SSD, which occurred in AOSD with APS. MRS was superior to diffusion MRI in detection of acute brain ischemia.