In the first part of this two-part series, I provided a brief overview of klotho and its biological function in the body. Here, I describe a recent study on the role of klotho in neurodegenerative diseases.
Researchers have recently discovered a new protective quality of klotho protein in the brain. Klotho is a known anti-aging protein that also contains anti-inflammatory properties. In a paper published in Nature Scientific Reports, Nakao et al. describe how klotho not only prevents inflammation but also prevents brain cell death. This study could point to a new role of klotho as a protective protein against neurodegenerative diseases and aging in the brain.
A common characteristic of aging in humans is that oftentimes, the brain develops low-grade, chronic inflammation. This is referred to as ‘inflammaging’ and is a strong risk factor for multiple diseases including cardiovascular disease, kidney disease, and depression among others. Heightened inflammation in the brain has also been associated with cognitive deficits related to aging as well as the progression of neurodegenerative diseases.
Interestingly, while klotho has primarily been studied in the context of inflammatory kidney diseases, the alpha-klotho form of the protein is highly abundant within the choroid plexus of the brain. This has led to the suspicion that klotho may play a large role in protecting the brain from inflammatory diseases and neurodegeneration.
To investigate the role of alpha-klotho in the brain, Nakao et al. sought to grow a culture of cells containing neurons and glial cells. Glial cells are important for supporting the health of neurons. In fact, a subset of glial cells called microglia and astrocytes form the immune system of the brain and are important for regulating neuroinflammation. Astrocytes in particular have been shown to activate the NF-kB inflammation cascade. Samples of both neurons and glial cells were taken from mice and cultured together.
To induce inflammation in their cell culture, Nakao et al. introduced lipopolysaccharides. Lipopolysaccharides are bacterial toxins that activate inflammation in the brain. They have been implicated in the activation of proinflammatory cytokines such as TNF-alpha, interleukin-1, and interleukin-6. By inducing the production of TNF-alpha, lipopolysaccharides have also been associated with promoting the NF-kB inflammation cascade.
The introduction of lipopolysaccharides allowed Nakao et al. to measure the levels of proinflammatory cytokines and NF-kB proteins in the cultured cells. This would also allow them to determine if alpha-klotho could successfully inhibit inflammation by halting the production of proinflammatory cytokines.
After determining that the lipopolysaccharides did in fact activate the production of proinflammatory cytokines like TNF-alpha, the researchers were ready to examine whether alpha-klotho could prevent an inflammatory response.
To do so, Nakao et al. pre-treated the neurons and glial cells with alpha-klotho. After twenty-four hours of exposure to klotho, the researchers then introduced lipopolysaccharides. To determine whether alpha-klotho prevented the activation of the NF-kB inflammation cascade, they examined a protein called RelA. RelA is a subunit of the NF-kB protein that is only released when the NF-kB inflammation cascade is activated. To their surprise, Nakao et al. found that cells that were pre-treated with alpha-klotho had significantly less RelA content, suggesting that alpha-klotho could successfully inhibit the activation of the NF-kB inflammation cascade.
While inflammation is a large component of aging, Nakao et al. were also interested in whether klotho could possibly play a protective role in the brain against neurodegenerative disorders. Neurodegenerative disorders like Alzheimer’s and Parkinson’s disease are defined by the progressive death of neuronal brain cells. If klotho could protect neurons from death, then perhaps the protein may play a larger role in preventing the progression of neurodegenerative diseases.
To test this, Nakao et al. first grew two samples of glial cells, one that was pre-treated with alpha-klotho and the other without. Lipopolysaccharides were then introduced to both samples to induce an immune response in the glial cells. By doing so, the glial cells would produce inflammatory proteins, releasing them into their surrounding solution. Nakao et al. then took samples of each culture’s solution and incorporated the samples into neuronal brain cell cultures.
The results showed that when the neurons were cultured with solution from glial cells that had been pre-treated with alpha-klotho, the neurons had a higher chance of survival. However, alpha-klotho seemed to only be protective to an extent—when neurons were treated with greater quantities of the glial cell solution, there was no difference in neuronal death even with the alpha-klotho pre-treatment.
Further research is required to determine the role of alpha-klotho in neurodegenerative diseases. However, klotho is clearly a fascinating protein with the potential to alter our understanding and treatment of both neurodegenerative diseases and aging. We eagerly await more information about this unique protein and its potential applications.