Therapeutic Potential of Leptin in Neurodegenerative Disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder, characterised by the build-up of amyloid beta (Aβ) plaques and neurofibrillary tangles comprising hyper-phosphorylated tau. Increasing evidence indicates that in the early stages of AD, elevated levels of oligomeric forms of Aβ and phosphorylated tau (p-tau) gives rise to impaired synaptic function which ultimately drives AD-associated cognitive abnormalities. Thus, developing drugs that can limit the synaptic impairments that occur early in AD may have therapeutic benefits. Clinical evidence increasingly supports a link between lifestyle choices and AD risk. Indeed, there is an association between the circulating levels of the metabolic hormone leptin, mid-life obesity and disease risk, which has in turn stimulated interest in targeting the leptin system to treat AD. It is well-established that leptin readily accesses the brain, with the hippocampus, a key region that degenerates in AD, identified as a prime target for this hormone. Within the hippocampus, leptin has cognitive enhancing properties as it markedly influences the cellular events underlying hippocampal-dependent learning and memory, with significant impact on synaptic plasticity and trafficking of glutamate receptors at hippocampal excitatory CA1 synapses. Moreover, studies using a range of cell-based systems and animal models of disease indicate not only that leptin has powerful pro-cognitive effects, but also that leptin protects against the unwanted synapto-toxic effects of Aβ and tau, as well as enhancing neuronal cell viability. Moreover, recent studies have demonstrated that smaller leptin-based molecules replicate the full repertoire of protective features of whole leptin. Here we review the evidence that the leptin system is a potential novel avenue for drug discovery in AD.