Identification of the neuronal receptor for the cognitive-enhancing soluble klotho ligand

Ageing is the main risk factor for cognitive decline, including problems with learning and memory. In this project we will focus on the anti-ageing protein, klotho, which has cognitive-enhancing properties. Klotho enhances the function of nerve cells, particularly the changes in synapses that are required for learning and memory. In addition, klotho protects nerve cells against oxidative damage which increases in the aged brain. These cognitive-enhancing properties of klotho are mediated by klotho interacting with an unknown receptor on the surface of nerve cells. We hypothesise that identification and characterisation of the receptor for klotho on human nerve cells will provide new opportunities for cognitive-enhancing strategies to combat age-related cognitive dysfunction. The objectives of this project are to take the essential next steps in exploring the cognitive-enhancing potential of klotho by: 1) identifying the receptor for klotho on the surface of human nerve cells; 2) validating the receptor for klotho in cells and brain tissue; and 3) determining the how the klotho receptor links to the beneficial changes in nerve cell function. We will use a range of state-of-the-art biochemical and cell biological approaches to address these objectives, and will link our findings to changes seen in the human brain by using human stem cell-derived neurons and post mortem human brain material. Identification of the klotho receptor will open the way to novel pharmacological approaches to mimic klotho activity in age-associated cognitive dysfunction.

Cognitive dysfunction is a key symptom of ageing. Strategies to enhance cognition would impact on quality of life for a significant proportion of our ageing population. The klotho protein protects against cognitive decline through enhancing NMDA receptor-dependent synaptic plasticity, which is required for learning and memory, and protecting neurons against oxidative damage. These effects of klotho are mediated by the proteolytically-shed soluble ectodomain (soluble klotho) through interaction with an unknown receptor on the surface of neurons. The objectives of this proposal are to take the essential next steps in exploring the cognitive-enhancing potential of klotho by: 1) identifying the receptor for soluble klotho on the surface of human induced-pluripotent stem cell-derived neurons by translating methods successfully used to isolate cell-surface integrins (chemical cross-linking, mass spectrometry identification) in conjunction with bioinformatics; 2) validating the ability of the receptor to mediate the effects of soluble klotho on NMDA receptor-dependent synaptic plasticity and protection against oxidative stress in cells and brain tissue using a combination of genetic and pharmacological approaches; and 3) determining the neuronal klotho receptor-induced signalling pathways that link to changes in synaptic plasticity and protection against oxidative damage using mass cytometry. Identification of the neuronal receptor for soluble klotho and its downstream signalling pathways will open the way to important new pharmacological approaches to mimic klotho activity in age-associated cognitive dysfunction.

Several groups stand to benefit from this research:
1) Individuals with age-associated cognitive dysfunction, including people with dementia, their carers and the general public.
Knowledge on the mechanism of action of soluble klotho is relevant to our understanding of how ageing processes impact on homeostasis/physiological function in cognitive systems, and how this can lead to age-related frailty and poor health. Information gained from this project may lead to strategies for improving lifelong health and wellbeing associated with age-associated cognitive dysfunction.

Future studies will use the information obtained to develop pharmacological probes/small molecules to assess the contribution of klotho to cognitive decline in ageing and in neurodegenerative disorders using in vivo models. Such molecules may prove valuable in slowing or halting the decline in cognition in ageing and age-related neurodegenerative diseases.

2) UK and world-wide health services.
As age-associated cognitive dysfunction is critically linked to age-related frailty and poor health, improving lifelong health and wellbeing associated with age-associated cognitive dysfunction will reduce pressure on the health and social care systems. Any intervention that slows, halts or reverses the cognitive decline that occurs on ageing or in dementia will have significant quality of life (and extension of life) benefits for the individual, and in addition reduced hospital and care home stays, with positive impact on the health and wealth of the nation.

3) Ageing researchers.
The results from this project will have significant impact on ageing researchers in a number of ways. Identification of the neuronal receptor for klotho and the signalling pathways elicited by klotho will be of interest as it will highlight alternative routes for delaying or halting age-associated dyshomeostasis. For the same reason, determination of the link between the identified receptor and the downstream effects of klotho on neuronal protection and synaptic plasticity will be of relevance to those interested in age-associated cognitive decline, including those with an interest in age-associated neurodegenerative diseases.

4) Researchers in other disciplines.
The approaches developed in this work will be a paradigm for studying other ligand-receptor interactions and thus will be of interest to a broader range of molecular and cellular researchers.

5) Researchers on this project.
This project is multidisciplinary and translational in its nature and provides an excellent training opportunity for all researchers involved. We will learn from the diverse skill set across the team. This project represents an excellent opportunity for developing research and transferable skills for use in future projects.