Carbonic anhydrase inhibitors clear tau build-up in zebrafish models of tauopathies
· News-MedicalA drug commonly used to treat glaucoma has been shown in zebrafish and mice to protect against the build-up in the brain of the protein tau, which causes various forms of dementia and is implicated in Alzheimer’s disease.
Tauopathies are neurodegenerative diseases characterised by the build-up in the brain of tau protein ‘aggregates’ within nerve cells. These include forms of dementia, Pick's disease and progressive supranuclear palsy, where tau is believed to be the primary disease driver, and Alzheimer’s disease and chronic traumatic encephalopathy (neurodegeneration caused by repeated head trauma, as has been reported in football and rugby players), where tau build-up is one consequence of disease but results in degeneration of brain tissue.
There has been little progress in finding effective drugs to treat these conditions. One option is to repurpose existing drugs. However, drug screening – where compounds are tested against disease models – usually takes place in cell cultures, but these do not capture many of the characteristics of tau build-up in a living organism.
To work around this, the Cambridge team turned to zebrafish models they had previously developed. Zebrafish grow to maturity and are able to breed within two to three months and produce large numbers of offspring. Using genetic manipulation, it is possible to mimic human diseases as many genes responsible for human diseases often have equivalents in the zebrafish.
Using this approach, the team showed that inhibiting an enzyme known as carbonic anhydrase – which is important for regulating acidity levels in cells – helped the cell rid itself of the tau protein build-up. It did this by causing the lysosomes – the ‘cell’s incinerators’ – to move to the surface of the cell, where they fused with the cell membrane and ‘spat out’ the tau.
When the team tested methazolamide on mice that had been genetically engineered to carry the P301S human disease-causing mutation in tau, which leads to the progressive accumulation of tau aggregates in the brain, they found that those treated with the drug performed better at memory tasks and showed improved cognitive performance compared with untreated mice.
Analysis of the mouse brains showed that they indeed had fewer tau aggregates, and consequently a lesser reduction in brain cells, compared with the untreated mice.
Fellow joint author Dr Farah Siddiqi, also from the Cambridge Institute for Medical Research and the UK Dementia Research Institute, said: “We were excited to see in our mouse studies that methazolamide reduces levels of tau in the brain and protects against its further build-up. It confirms what we’d shown when screening carbonic anhydrase inhibitors using zebrafish models of tauopathies.”
Professor Rubinsztein, UK Dementia Research Institute and Cambridge Institute for Medical Research, University of CambridgeMethazolamide shows promise as a much-needed drug to help prevent the build-up of dangerous tau proteins in the brain. Although we’ve only looked at its effects in zebrafish and mice, so it is still early days, we at least know about this drug’s safety profile in patients. This will enable us to move to clinical trials much faster than we might normally expect if we were starting from scratch with an unknown drug compound. This shows how we can use zebrafish to test whether existing drugs might be repurposed to tackle different diseases, potentially speeding up significantly the drug discovery process.”
The team hopes to test methazolamide on different disease models, including more common diseases characterized by the build-up of aggregate-prone proteins, such as Huntington’s and Parkinson’s diseases.
The research was supported by the UK Dementia Research Institute (through UK DRI Ltd, principally funded through the Medical Research Council), Tau Consortium and Wellcome.
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Journal reference:
Lopez, A., et al. (2024). Carbonic anhydrase inhibition ameliorates tau toxicity via enhanced tau secretion. Nature Chemical Biology. doi.org/10.1038/s41589-024-01762-7.