Excitotoxicity has been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). More recently, glial involvement has been shown to be essential for ALS‐related motoneuronal death. Here, we identified an N ‐methyl‐d‐aspartate (NMDA) receptor co‐agonist, d‐serine (d‐Ser), as a glia‐derived enhancer of glutamate (Glu) toxicity to ALS motoneurons. Cell death assay indicated that primary spinal cord neurons from ALS mice were more vulnerable to NMDA toxicity than those from control mice, in a d‐Ser‐dependent manner. Levels of d‐Ser and its producing enzyme, serine racemase, in spinal cords of ALS mice were progressively elevated, dominantly in glia, with disease progression. In vitro , expression of serine racemase was induced not only by an extracellular pro‐inflammatory factor, but also by transiently expressed G93A‐superoxide dismutase1 in microglial cells. Furthermore, increases of d‐Ser levels were also observed in spinal cords of both familial and sporadic ALS patients. Collectively, Glu toxicity enhanced by d‐Ser overproduced in glia is proposed as a novel mechanism underlying ALS motoneuronal death, and this mechanism may be regarded as a potential therapeutic target for ALS.

Elevation of intracranial soluble amyloid-β (Aβ) levels has been implicated in the pathogenesis of Alzheimer's disease (AD). Intracellular events in neurons, which lead to memory loss in AD, however, remain elusive. Humanin (HN) is a short neuroprotective peptide abolishing Aβ neurotoxicity. Recently, we found that HN derivatives activate the Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling axis. We here report that an HN derivative named colivelin completely restored cognitive function in an AD model (Tg2576) by activating the JAK2/STAT3 axis. In accordance, immunofluorescence staining using a specific antibody against phospho- (p-) STAT3 revealed that p-STAT3 levels in hippocampal neurons age-dependently decreased in both AD model mice and AD patients. Intracerebroventricular administration of Aβ1–42 downregulated p-STAT3 whereas passive immunization with anti-Aβ antibody conversely restored hippocampal p-STAT3 levels in Tg2576 mice, paralleling the decrease in the brain Aβ burden. Aβ1–42 consistently modulated p-STAT3 levels in primary neurons. Pharmacological inhibition of the JAK2/STAT3 axis not only induced significant loss of spatial working memory by downregulating an acetylcholine-producing enzyme choline acetyltransferase but also desensitized the M₁-type muscarinic acetylcholine receptor. Thus, we propose a novel theory accounting for memory impairment related to AD: Aβ-dependent inactivation of the JAK2/STAT3 axis causes memory loss through cholinergic dysfunction. Our findings provide not only a novel pathological hallmark in AD but also a novel target in AD therapy.

(2009). Targeting the JAK2/STAT3 axis in Alzheimer's disease. Expert Opinion on Therapeutic Targets: Vol. 13, No. 10, pp. 1155-1167. doi: 10.1517/14728220903213426

Alzheimer's disease (AD) is the most common cause of dementia. Humanin (HN) is a short bioactive peptide abolishing neuronal cell death induced by various familial AD (FAD)-causative genes and amyloid-β (Aβ)in vitro. It has been shown that HN suppresses memory impairment of mice induced by intracerebroventricular administration of Aβ. To potentiate the neuroprotective effect of HN, we synthesized a hybrid peptide named Colivelin composed of activity-dependent neurotrophic factor (ADNF) C-terminally fused to AGA-(C8R)HNG17, a potent HN derivative. Colivelin completely suppresses death induced by overexpressed FAD-causative genes and Aβ1-43 at a concentration of 100 fm, whereas AGA-(C8R)HNG17 does so at a concentration of 10 pm. Colivelin-induced neuroprotection has been confirmed to occur via two neuroprotective pathways: one mediated by Ca²⁺/calmodulin-dependent protein kinase IV, triggered by ADNF, and one mediated by signal transducer and activator of transcription 3, triggered by HN.In vivoanimal studies have further indicated that intracerebroventricular administration of Colivelin not only completely suppresses impairment in spatial working memory induced by repetitive intracerebroventricular injection of Aβ25-35 or Aβ1-42, but also it antagonizes neuronal loss in the CA1 region of hippocampus induced by hippocampal injection of Aβ1-42. In addition, intraperitoneally administered Colivelin suppresses memory impairment caused by a muscarinic acetylcholine receptor antagonist, 3-quinuclidinyl benzilate, indicating that a substantial portion of intraperitoneally administered Colivelin passes through the blood-brain barrier and suppresses functional memory deficit. Thus, Colivelin might serve as a novel drug candidate for treatment of AD.