New research in humans published today reveals that the so-called FKBP52 protein may prevent the Tau protein from turning pathogenic. This may prove significant for the development of new Alzheimer’s drugs and for detecting the disease before the onset of clinical symptoms.
A study published online today in the Journal of Alzheimer’s Disease (1), for the first time demonstrates that the FKBP52 protein, discovered by Prof. Etienne BAULIEU twenty years ago, may prevent hyperphosphorylation of Tau protein, which has been shown to characterise a number of cerebral neurodegenerative diseases, including Alzheimer’s Disease (AD).
This work has been carried out by Professor Etienne Baulieu and his research team at Inserm (National Institute for medical research in France) with the support of philanthropists who help the Institut Baulieu, based in France.
Limited research exists on Tau and its role in the development of AD, but it is known that many neurodegenerative diseases are characterised by the deposition of pathological hyperphosphorylated forms of Tau protein, into structures known as ‘Tau tangles’. The mechanism of Tau toxicity is unclear and there are currently no drug treatments targeting Tau, nor any biomarkers that predict the risk of a future “Tauopathy”. Professor Baulieu decided to focus on Tau abnormalities and was the first to discover in 2010, an interaction between Tau, and the FKBP52 protein (2).
The new research takes his previous research to the next level. It demonstrates a direct correlation between high levels of hyperphosphorylated Tau protein and reduced levels of FKBP52, in brain cells from patients who have died following Alzheimer’s Disease, compared with normal brain cells. This suggests that FKBP52 could control the aberrant production of pathogenic Tau. When FKBP52 is reduced in the nerve cells of AD patients, pathogenic Tau is free to accumulate and contribute to the degeneration of brain cells.
In conclusion, early measurement of FKBP52 levels could form the basis of a predictive test for Alzheimer’s Disease before the onset of clinical symptoms, and new compounds modulating FKBP52’s activity could become the next generation of treatments for the disease.
FK506-binding protein 4 is a protein that in humans is encoded by the FKBP4 gene.
The protein encoded by this gene is a member of the immunophilin protein family, which play a role in immunoregulation and basic cellular processes involving protein folding and trafficking. This encoded protein is a cis-trans prolyl isomerase that binds to the immunosuppressants FK506 and rapamycin. It has high structural and functional similarity to FK506-binding protein 1A (FKBP1A), but unlike FKBP1A, this protein does not have immunosuppressant activity when complexed with FK506. It interacts with interferon regulatory factor-4 and plays an important role in immunoregulatory gene expression in B and T lymphocytes. This encoded protein is known to associate with phytanoyl-CoA alpha-hydroxylase. It can also associate with two heat shock proteins (hsp90 and hsp70) and thus may play a role in the intracellular trafficking of hetero-oligomeric forms of the steroid hormone receptors. This protein correlates strongly with adeno-associated virus type 2 vectors (AAV) resulting in a significant increase in AAV-mediated transgene expression in human cell lines. Thus this encoded protein is thought to have important implications for the optimal use of AAV vectors in human gene therapy. This gene has been found to have multiple polyadenylation sites.
Commenting on this new research, Professor Baulieu said: “There is still a worrying lack of research into the causes of age-related brain disorders such as Alzheimer’s Disease and dementia. I founded the Institut Baulieu, with the aim of being able to treat and even prevent these diseases.
Research on Tau has been very limited, and until recently, I was among the few scientists focusing on Tau pathology. The discovery of the FKBP52 protein is the only ‘anti-Tau’ perspective so far. Its reduced production in the brains of Alzheimer’s patients marks a turning point in understanding this complex disease.
A role for FKBP52 in Tau protein function
Tau is a microtubule-associated protein, which is widely expressed in the central nervous system, predominantly in neurons, where it regulates microtubule dynamics, axonal transport, and neurite outgrowth. The aberrant assembly of Tau is the hallmark of several human neurodegenerative diseases, collectively known as tauopathies. They include Alzheimer’s disease, Pick’s disease, progressive supranuclear palsy, and frontotemporal dementia and parkinsonism linked to chromosome 17. Several abnormalities in Tau, such as hyperphosphorylation and aggregation, alter its function and are central to the pathogenic process. Here, we describe biochemical and functional interactions between FKBP52 and Tau. FKBP52 is a member of the FKBP (FK506-binding protein) family that comprises intracellular protein effectors of immunosuppressive drugs (such as FK506 and rapamycin). We found that FKBP52, which is abundant in brain, binds directly and specifically to Tau, especially in its hyperphosphorylated form. The relevance of this observation was confirmed by the colocalization of both proteins in the distal part of the axons of cortical neurons and by the antagonistic effect of FKBP52 on the ability of Tau to promote microtubule assembly. Overexpression of FKBP52 in differentiated PC12 cells prevented the accumulation of Tau and resulted in reduced neurite length. Taken together, these findings indicate a role for FKBP52 in Tau function and may help to decipher and modulate the events involved in Tau-induced neurodegeneration.
I believe it takes us one step closer to developing an effective treatment and possible predictive tests for the increasing number of people who may develop Alzheimer’s Disease in our ageing societies.”