Disruption of leptin signalling has been implicated as playing a role in the development of Alzheimer's disease (AD). Leptin has previously been shown to be affected by amyloid-beta (Aβ)-related signalling; however, pathways that link leptin to the disease pathogenesis have not been determined. To characterize the association between increasing age-dependent Aβ levels with leptin signalling and the vulnerable brain regions in AD, we assessed the mRNA and protein expression profile of leptin and leptin receptor (Ob-Rb) at 9 and 18-month-age in APP/PS1 mice. Immunohistochemical labelling demonstrated that leptin and Ob-Rb proteins were localised to neocortical and hippocampal neurons in APP/PS1 and wildtype (WT) mice. Neuronal leptin and Ob-Rb immunolabelling was more prominent in the neocortex of both groups at 9 month of age, while, at 18 months, labelling was reduced in the hippocampus of APP/PS1 mice relative to WT. Immunoblotting analysis demonstrated decreased hippocampal leptin levels, concomitantly with an increased Ob-Rb levels, in APP/PS1 mice compared with WT controls at 18 month of age. While no leptin mRNA was found in either of the groups analysed, Ob-Rb mRNA was significantly decreased in the hippocampus of APP/PS1 mice at both ages analysed. In addition, a significant decreased protein kinase B (Akt) activity concomitantly with an upregulation of suppressor of cytokine signaling-3 (SOCS3) and protein-tyrosine phosphatase 1B (PTP1B) transcripts was present. Thus, these results collectively indicate alterations of leptin signalling in the hippocampus of APP/PS1 mice, providing novel insights about the pathways that could link aberrant leptin signaling to the pathological changes of AD.

Axon degeneration has been implicated as a pathological process in several neurodegenerative diseases and acquired forms of neural injury. We have previously shown that stabilizing microtubules can protect axons against excitotoxin-induced fragmentation, however, the alterations of microtubules following excitotoxicity that results in axon degeneration are currently unknown. Hence, this study investigated whether excitotoxicity affects the post-translational modifications of microtubules and microtubule-associated proteins, and whether reversing these changes has the potential to rescue axons from degeneration. To investigate microtubule alterations, primary mouse cortical neurons at 10 days in vitro were treated with 10 or 25 μM kainic acid to induce excitotoxicity and axon degeneration. Post-translational modifications of microtubules and associated proteins were examined at 6 h following kainic acid exposure, relative to axon degeneration. While there were no changes to tyrosinated tubulin or MAP1B, acetylated tubulin was significantly (p < 0.05) decreased by 40% at 6 h post-treatment. To determine whether increasing microtubule acetylation prior to kainic acid exposure could prevent axon fragmentation, we investigated the effect of reducing microtubule deacetylation with the HDAC6 inhibitor, trichostatin A. We found that trichostatin A prevented kainic acid-induced microtubule deacetylation and significantly (p < 0.05) protected axons from fragmentation. These data suggest that microtubule acetylation is a potential target for axonal protection where excitotoxicity may play a role in neuronal degeneration.

Background: Alzheimer’s disease (AD) has challenged single-target therapeutic strategies, raising the possibility that combined therapies may offer a more effective treatment strategy. Objective: There is substantial evidence for the efficacy of leptin (L) (neuroprotective hormone) and pioglitazone (P) (anti-inflammatory agent) as monotherapies in AD. We have previously shown that combination treatment of L+P in APP/PS1 mice at the onset of pathology significantly improved memory and reduced brain Aβ levels relative to control mice. In this new study, we sought to replicate our previous findings in a new cohort of APP/PS1 mice to further confirm whether the combined treatment of L+P is superior to each treatment individually. Method: We have re-evaluated the effects of L+P co-treatment in APP/PS1 mice using thioflavin-S staining, MOAβ immunolabeling, and enzyme-linked immunosorbent assay (ELISA) to examine effects on Aβ levels and pathology, relative to animals that received L or P individually. Results: We demonstrated that a combination of L and P significantly enhances the anti-Aβ effect of L or P in the hippocampus of APP/PS1 mice. Conclusion: Our findings suggest that combining L and P significantly enhances the anti-Aβ effect of L or P in the hippocampus of APP/PS1 mice and maybe a potential new effective strategy for AD ther- apy.

Axon degeneration and axonal loss is a feature of neurodegenerative disease and injury and occurs via programmed pathways that are distinct from cell death pathways. While the pathways of axonal loss following axon severing are well described, less is known about axonal loss following other neurodegenerative insults. Here we use primary mouse cortical neuron cultures grown in compartmentalized chambers to investigate the role of calcium in the degeneration of axons that occurs following a somal insult by the excitotoxin kainic acid. Calcium influx has been implicated in both excitotoxicity and axon degeneration mechanisms, however the link between a somal insult and axonal calcium increase is unclear. Live imaging of axons demonstrated that pharmacologically preventing intracellular calcium increases through the endoplasmic reticulum or mitochondria significantly (p < 0.05) reduced axon degeneration. Live calcium‐imaging with the Ca2+ indicator Fluo‐4 demonstrated that kainic acid exposure to the soma resulted in a rapid, and transient, increase in calcium in the axon, which occured even at low kainic acid concentrations that do not cause axon degeneration within 24 h. However, this calcium transient was followed by a gradual increase in axonal calcium, which was associated with axonal loss. Furthermore, treatment with a range of doses of the microtubule stabilizing drug taxol, which protects against axon fragmentation in this model, prevented this gradual calcium increase, suggesting that the intra‐axonal calcium changes are downstream of microtubule associated events. Biochemical analysis of taxol treated neurons demonstrated a shift in microtubule post‐translational modifications, with a significant (p < 0.05) increase in acetylated tubulin and a significant (p < 0.05) decrease in tyrosinated tubulin, suggestive of a more stable microtubule pool. Together our results suggest that axonal degeneration following excitotoxicity is dependent on an increase in axonal calcium, which is downstream of a microtubule‐dependent event.

Cognitive dysfunction is a key symptom of aging and neurodegenerative disorders, such as Alzheimer’s disease. Strategies to enhance cognition would impact the quality of life for a significant proportion of the ageing population. The ɑ-klotho protein may protect against cognitive decline through multiple mechanisms: such as promoting optimal synaptic function via activation of N-methyl-D-aspartate receptor signalling; stimulating the anti-oxidant defence system; reducing inflammation; promoting autophagy; and enhancing clearance of amyloid-β. However, the molecular and cellular pathways by which ɑ-klotho mediates these neuroprotective functions have yet to be fully elucidated. Key questions remain unanswered: which form of ɑ-klotho (transmembrane, soluble or secreted) mediates its cognitive enhancing properties; what is the neuronal receptor for ɑ-klotho and which signalling pathways are activated by ɑ-klotho in the brain to enhance cognition; how does peripherally administered ɑ-klotho mediate neuroprotection; and what is the molecular basis for the beneficial effect of the VS variant of ɑ-klotho? In this review we summarise the recent research on neuronal ɑ-klotho and discuss how the neuroprotective properties of ɑ-klotho could be exploited to tackle age- and neurodegeneration-associated cognitive dysfunction.