Humanin derivative, HNG, enhances neurotransmitter release.

BACKGROUND: Humanin (HN) is an endogenous 24-residue peptide that was first identified as a protective factor against neuronal death in Alzheimer's disease (AD). We previously demonstrated that the highly potent HN derivative HNG (HN with substitution of Gly for Ser14) ameliorated cognitive impairment in AD mouse models. Despite the accumulating evidence on the antagonizing effects of HN against cognitive deficits, the mechanisms behind these effects remain to be elucidated. METHODS: The extracellular fluid in the hippocampus of wild-type young mice was collected by microdialysis and the amounts of neurotransmitters were measured. The kinetic analysis of exocytosis was performed by amperometry using neuroendocrine cells. RESULTS: The hippocampal acetylcholine (ACh) levels were increased by intraperitoneal injection of HNG. HNG did not affect the physical activities of the mice but modestly improved their object memory. In a neuronal cell model, rat pheochromocytoma PC12 cells, HNG enhanced ACh-induced dopamine release. HNG increased ACh-induced secretory events and vesicular quantal size in primary neuroendocrine cells. CONCLUSIONS: These findings suggest that HN directly enhances regulated exocytosis in neurons, which can contribute to the improvement of cognitive functions. GENERAL SIGNIFICANCE: The regulator of exocytosis is a novel physiological role of HN, which provides a molecular clue for HN's effects on brain functions under health and disease.

Behavioral and electrophysiological evidence for a neuroprotective role of aquaporin-4 in the 5xFAD transgenic mice model.

Aquaporin-4 (AQP4) has been suggested to be involved in the pathogenesis of neurodegenerative diseases including Alzheimer's disease (AD), which may be due to the modulation of neuroinflammation or the impairment of interstitial fluid bulk flow system in the central nervous system. Here, we show an age-dependent impairment of several behavioral outcomes in 5xFAD AQP4 null mice. Twenty-four-hour video recordings and computational analyses of their movement revealed that the nighttime motion of AQP4-deficient 5xFAD mice was progressively reduced between 20 and 36 weeks of age, with a sharp deterioration occurring between 30 and 32 weeks. This reduction in nighttime motion was accompanied by motor dysfunction and epileptiform neuronal activities, demonstrated by increased abnormal spikes by electroencephalography. In addition, all AQP4-deficient 5xFAD mice exhibited convulsions at least once during the period of the analysis. Interestingly, despite such obvious phenotypes, parenchymal amyloid ß (Aß) deposition, reactive astrocytosis, and activated microgliosis surrounding amyloid plaques were unchanged in the AQP4-deficient 5xFAD mice relative to 5xFAD mice. Taken together, our data indicate that AQP4 deficiency greatly accelerates an age-dependent deterioration of neuronal function in 5xFAD mice associated with epileptiform neuronal activity without significantly altering Aß deposition or neuroinflammation in this mouse model. We therefore propose that there exists another pathophysiological phase in AD which follows amyloid plaque deposition and neuroinflammation and is sensitive to AQP4 deficiency.

Humanin affects object recognition and gliosis in short-term cuprizone-treated mice.

Humanin (HN) is a 24-residue peptide that manipulates cell survival under various stresses. A highly potent HN derivative, HNG, reduced amyloid burden and neuroinflammation and suppressed cognitive impairment in Alzheimer's disease model mice. Cuprizone (CPZ), a copper chelator, provokes demyelination in the central nervous system of mice. A shorter (one week) exposure to CPZ induces schizophrenia-like behavior and glial activation prior to demyelination. We tested the effect of HNG on these short-term responses to CZP in mice. Intraperitoneal injection of HNG for one week improved object recognition memory but not working memory in CPZ-treated mice. Quantitative PCR analyses showed that HNG significantly suppressed CPZ-induced activation of microglia, but did not alter the reduced level of a myelin-specific transcript. These results suggest that HN can suppress neuroinflammation and the associated cognitive deficit in a wider range of neurological disorders beyond Alzheimer's disease.

Humanin ameliorates diazepam-induced memory deficit in mice.

Humanin (HN) is an endogenous 24-residue peptide. A highly potent HN derivative, S14G-HN, which has a substitution of serine 14 to glycine, reduced amyloid burden and suppressed cognitive impairment in a mouse model of Alzheimer's disease. S14G-HN also suppressed amnesia induced by a muscarinic receptor antagonist in rodents. To understand the effects of HN on brain function, we tested the effect of S14G-HN on diazepam (DZP)-induced memory impairment and anxiety in mice using the object recognition test and zero-maze test, respectively. Intraperitoneal injection of S14G-HN reversed the DZP-induced memory deficit, whereas no significant change was observed in behavioral markers of anxiety. S14G-HN had no effect on locomotor activity in either test, indicating that S14G-HN did not affect physical functioning or motivation. These results suggest that HN preferentially influences cognitive function but not emotional function in the central nervous system.