Protein Tyrosine Phosphatase 1B (PTP1B): A Potential Target for Alzheimer’s Therapy?

Defective brain insulin signaling has been suggested to contribute to the cognitive deficits in patients with Alzheimer's disease (AD). Although a connection between AD and diabetes has been suggested, a major unknown is the mechanism(s) by which insulin resistance in the brain arises in individuals with AD. Here, we show that serine phosphorylation of IRS-1 (IRS-1pSer) is common to both diseases. Brain tissue from humans with AD had elevated levels of IRS-1pSer and activated JNK, analogous to what occurs in peripheral tissue in patients with diabetes. We found that amyloid-β peptide (Aβ) oligomers, synaptotoxins that accumulate in the brains of AD patients, activated the JNK/TNF-α pathway, induced IRS-1 phosphorylation at multiple serine residues, and inhibited physiological IRS-1pTyr in mature cultured hippocampal neurons. Impaired IRS-1 signaling was also present in the hippocampi of Tg mice with a brain condition that models AD. Importantly, intracerebroventricular injection of Aβ oligomers triggered hippocampal IRS-1pSer and JNK activation in cynomolgus monkeys. The oligomer-induced neuronal pathologies observed in vitro, including impaired axonal transport, were prevented by exposure to exendin-4 (exenatide), an anti-diabetes agent. In Tg mice, exendin-4 decreased levels of hippocampal IRS-1pSer and activated JNK and improved behavioral measures of cognition. By establishing molecular links between the dysregulated insulin signaling in AD and diabetes, our results open avenues for the investigation of new therapeutics in AD. Show more

Profound neuronal dysfunction in the entorhinal cortex contributes to early loss of short-term memory in Alzheimer's disease. Here we show broad neuroprotective effects of entorhinal brain-derived neurotrophic factor (BDNF) administration in several animal models of Alzheimer's disease, with extension of therapeutic benefits into the degenerating hippocampus. In amyloid-transgenic mice, BDNF gene delivery, when administered after disease onset, reverses synapse loss, partially normalizes aberrant gene expression, improves cell signaling and restores learning and memory. These outcomes occur independently of effects on amyloid plaque load. In aged rats, BDNF infusion reverses cognitive decline, improves age-related perturbations in gene expression and restores cell signaling. In adult rats and primates, BDNF prevents lesion-induced death of entorhinal cortical neurons. In aged primates, BDNF reverses neuronal atrophy and ameliorates age-related cognitive impairment. Collectively, these findings indicate that BDNF exerts substantial protective effects on crucial neuronal circuitry involved in Alzheimer's disease, acting through amyloid-independent mechanisms. BDNF therapeutic delivery merits exploration as a potential therapy for Alzheimer's disease. Show more

Type 2 diabetes is a risk factor for Alzheimer's disease, most likely linked to an impairment of insulin signaling in the brain. The incretin hormone glucagon-like peptide-1 (GLP-1) facilitates insulin signaling, and novel long-lasting GLP-1 analogs, such as liraglutide, are on the market as diabetes therapeutics. GLP-1 has been shown to have neuroprotective properties in vitro and in vivo. Here we tested the effects of peripherally injected liraglutide in an Alzheimer mouse model, APP(swe)/PS1(ΔE9) (APP/PS1). Liraglutide was shown to cross the blood-brain barrier in an acute study. Liraglutide was injected for 8 weeks at 25 nmol/kg body weight i.p. once daily in 7-month-old APP/PS1 and wild-type littermate controls. In APP/PS1 mice, liraglutide prevented memory impairments in object recognition and water maze tasks, and prevented synapse loss and deterioration of synaptic plasticity in the hippocampus, commonly observed in this model. Overall β-amyloid plaque count in the cortex and dense-core plaque numbers were reduced by 40-50%, while levels of soluble amyloid oligomers were reduced by 25%. The inflammation response as measured by activated microglia numbers was halved in liraglutide-treated APP/PS1 mice. Numbers of young neurons in the dentate gyrus were increased in APP/PS1 mice with treatment. Liraglutide treatment had little effect on littermate control mice, whose behavior was comparable to wild-type saline controls; however, synaptic plasticity was enhanced in the drug group. Our results show that liraglutide prevents key neurodegenerative developments found in Alzheimer's disease, suggesting that GLP-1 analogs represent a novel treatment strategy for Alzheimer's disease. Show more