Activation of a synapse weakening pathway by human Val66 but not Met66 pro-brain-derived neurotrophic factor (proBDNF)

Sumangali Kailainathan,Thomas M Piers,Jee Hyun Yi,Seongmin Choi,Mark S Fahey,Eva Borger,Frank J Gunn-Moore,Laurie O’Neill,Michael Lever,Daniel J Whitcomb,Kwangwook Cho,Shelley J Allen

doi:10.1016/j.phrs.2015.12.008

Abstract

This study describes a fundamental functional difference between the two main polymorphisms of the pro-form of brain-derived neurotrophic factor (proBDNF), providing an explanation as to why these forms have such different age-related neurological outcomes. Healthy young carriers of the Met66 form (present in ∼30% Caucasians) have reduced hippocampal volume and impaired hippocampal-dependent memory function, yet the same polymorphic population shows enhanced cognitive recovery after traumatic brain injury, delayed cognitive dysfunction during aging, and lower risk of late-onset Alzheimer’s disease (AD) compared to those with the more common Val66 polymorphism. To examine the differences between the protein polymorphisms in structure, kinetics of binding to proBDNF receptors and in vitro function, we generated purified cleavage-resistant human variants. Intriguingly, we found no statistical differences in those characteristics. As anticipated, exogenous application of proBDNF Val66 to rat hippocampal slices dysregulated synaptic plasticity, inhibiting long-term potentiation (LTP) and facilitating long-term depression (LTD). We subsequently observed that this occurred via the glycogen synthase kinase 3β (GSK3β) activation pathway. However, surprisingly, we found that Met66 had no such effects on either LTP or LTD. These novel findings suggest that, unlike Val66, the Met66 variant does not facilitate synapse weakening signaling, perhaps accounting for its protective effects with aging.

Highlights

In order to establish whether physical differences between them could account for their contrasting effects in cognitive function, these polymorphic proteins were produced as cleavage-resistant forms and compared directly for the first time for differences in structure, receptor binding kinetics and function
In order to try to explain the age-related functional differences seen in carriers of the common Val66Met polymorphism, the separate human recombinant proteins were produced and the biophysical, kinetic, cellular and synaptic differences between the two common pro-form of brain-derived neurotrophic factor (proBDNF) polymorphisms were assessed
Neither could the polymorphisms be differentiated in terms of their binding kinetics to receptor binding domains

Summary

Introduction

␤-D-1-thiogalactopyranoside; LDH, lactate dehydrogenase; LTD, long-term depression; LTP, long-term potentiation; LD, luminal domain; NAD, nicotinamide adenine dinucleotide; p75NTR, pan-neurotrophin receptor; PMS, phenazinemethosulfate; PONDR, predictor of naturally disordered regions; RU, response units; SNP, single nucleotide polymorphism; SDS PAGE, sodium dodecyl sulfate polyacrylamide electrophoresis; s.e.m., standard error of mean; SPR, surface plasmon resonance; The neurotrophin brain-derived neurotrophic factor (BDNF) is first translated as the precursor form, proBDNF. Studies show a slower overall cognitive decline with increasing age in healthy proBDNF Met carriers [4,5,6,7] compared with Val. Evidence would suggest that Met confers some neuroprotective effects that are not present with Val. Evidence would suggest that Met confers some neuroprotective effects that are not present with Val66 Why this is the case and the mechanisms responsible, remain to be fully explained

Methods

Results

Discussion

Conclusion