Klotho protein in Alzheimer's disease: Diet leading to immortality?

Introduction

Klotho was a Greek goddess, the youngest of Morari—personifications of destiny. She spins the thread of human life. ¹ Why did she give the name to the protein discovered in 1997? Probably due to its anti-aging functions which allow it to spin the thread of human life longer. ² Kuro-o et al. ¹ have identified new molecules while creating transgenic mice. Since 1997 this protein has begun to interest scientists all over the world wishing to discover the mystery of aging. Will Klotho protein help to create medicine that stops aging? Or maybe even make humans immortal?

However, this molecule may be also used in creating therapies for patients suffering from diseases which are incurable today, in particular neurodegenerative diseases like Alzheimer's disease (AD), Parkinson's disease or multiple sclerosis. In our work we would like to focus on the first condition. This is the most common type of dementia, currently affecting 50 million people worldwide and the number is growing. ³

Recent studies show that Klotho protein level is dependent on type of food. While the role of Klotho in aging and neurodegeneration has been extensively reviewed, the impact of diet on Klotho expression remains relatively underexplored. Most existing reviews focus on genetic regulation and pharmacological modulation of Klotho, with limited discussion on how specific dietary components influence its levels and function. Given the growing evidence linking nutrition to Klotho expression and cognitive health, further exploration of dietary strategies to enhance Klotho activity could provide new perspectives on AD prevention and treatment.

Alzheimer's disease: main facts

AD is the most common cause of dementia in people aged 65 and above. ⁴ 5–8% people over 65 suffer from dementia and, as incidence of disease increases with age, 20–25% at the age over 85 is affected. ⁵

It was first described in 1907 by Alois Alzheimer. ⁶ In his case report, he connected syndromes of dementia with neuropathological findings—intracellular neurofibrillary tangles and extracellular plaques. Nowadays we know that plaques contain amyloid-β (Aβ) and that neurofibrillary tangles are built mostly of tau. ⁷

AD is associated with several risk factors such as genetic factors, increasing age, head injuries, infections, vascular diseases and environmental factors. ⁸

Typically AD manifests as amnestic cognitive impairment in which the severity of symptoms depends on the stage of the disease. Prototypical clinical phenotype of AD is progressive dementia with prominent amnestic symptoms. At the early stage, AD patients may declare subjective decline in mental abilities while objective cognitive testing may not reveal any abnormalities. ⁹ As the disease progresses, problems with short-term memory, spatial orientation, impaired language skills and aphasia appear. ¹⁰

Currently there are three classes of pharmacological therapy for patients with AD. The first group of drugs most commonly used in the treatment of AD are cholinesterase inhibitors, intended for the treatment of mild, moderate, and severe forms of dementia. Cholinesterase inhibitors include donepezil, galantamine, and rivastigmine. ¹¹ The only representative of the second class of drugs is memantine, which is dedicated for patients with moderate to severe AD. Memantine is mainly non-competitive N-methyl-D-aspartate receptor antagonist. The newest class of drugs are monoclonal antibodies directed against Aβ deposits. Aducanumab and lecanemab have already been introduced for the treatment of AD, and donanemab is next. Some enthusiastically call therapy with these drugs a new era of AD treatment.

Structure and function of Klotho protein

Klotho is the protein that is highly associated with the aging process, which led to much research being conducted last decade. However, the aging process is not completely clear. What we know now is that Klotho insufficiency is linked with aging.

In humans, Klotho is a single-pass membrane protein consisting of two extracellular domains KL1 and KL2. There are three isoforms α-, β-, and γ-Klotho. β-Klotho is largely expressed in the liver, gut and spleen while γ-Klotho in skin and kidney. ¹² α- Klotho is the best known isoform, and it is expressed mostly in kidneys and in smaller amounts in brain choroid plexus.^13,14 α- Klotho consists of two extracellular domains KL1 and KL2. Cleaved by proteases, such as ADAM10 and ADAM17 (α-proteases), Klotho protein becomes soluble Klotho. Soluble Klotho is a major form detected in body fluids and in this specific form it acts as an endocrine hormone, affecting many tissues. ¹⁵ There are many factors that increase expression of α-proteases and α-Klotho such as insulin, growth factors, and cytokines. ¹⁶ Inhibition of α-proteases is caused by tissue inhibitors of metalloproteinases. ¹⁷ Recent studies show that ligustilide, a natural compound stored in celery can also increase expression of α-Klotho in models of mice with AD. ¹⁸

Extracellular domains of Klotho proteins bind to FGFR1 to create a high affinity receptor for FGF23. FGF23 is bone-derived protein that regulates concentration of phosphate in plasma (increasing exertion in and vitamin D metabolism). ¹⁹ Klotho supplementation reduces cellular aging by inhibiting the p53/p21 signaling pathway which is responsible for cell death. ²⁰ The deficiency of Klotho protein results in excessive expression of p53/p21 proteins. ²¹

Klotho is increasingly recognized for its neuroprotective properties, particularly in the context of AD. Beyond its role in aging and metabolic regulation, recent research suggests that Klotho influences key pathological processes in AD, including Aβ accumulation, tau hyperphosphorylation, oxidative stress, and neuroinflammation. Recent studies highlight Klotho's neuroprotective role in AD through multiple mechanisms, including enhanced Aβ clearance via neprilysin upregulation and inhibition of β-secretase (BACE1), reducing amyloid accumulation. Additionally, Klotho modulates tau pathology by suppressing glycogen synthase kinase-3β activity, thereby preventing tau hyperphosphorylation and promoting autophagic clearance of tau aggregates. ²² It also mitigates neuroinflammation by downregulating NF-κB signaling and pro-inflammatory cytokines while enhancing mitochondrial function and antioxidant defense systems to counteract oxidative stress. These combined actions position Klotho as a promising target for AD therapy, with ongoing research focusing on strategies to boost its expression through pharmacological and lifestyle interventions. ²³ (Figure 1)

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Figure 1.

Structure and function of Klotho protein.

Klotho expression in the hippocampus

Klotho protein is found in organs such as the pituitary glands, parathyroid gland, skeletal muscles, brain, testes, kidneys, inner ear, ovaries, colon, and breast epithelial cells in its transmembrane form. Mapping the presence of Klotho protein in the brain proved that Klotho protein expression is strongest in the choroid plexus and significant in the brain parenchyma. The presence of Klotho protein was confirmed in the gray matter, including the cerebral cortex and hippocampus. ²⁴ The hippocampus is responsible for memory and plays a central role in learning. It is particularly vulnerable to inflammatory injury due to its high density of receptors for inflammatory mediators. The hippocampus in older people undergoes cognitive deterioration, which is also observed in neurodegenerative diseases such as AD. Although hippocampal degeneration is also observed in dementia with Lewy bodies, the degree of deterioration is much greater in AD. ²⁵ Klotho overexpression may have a beneficial effect on the aging brain and have a positive effect on neurodegenerative conditions. ²⁶ Hippocampal neurons are protected by Klotho protein from amyloid and glutamate toxicity. The protection works by activating an antioxidant enzyme system. Based on this, we can conclude that Klotho is a neuroprotective protein. Moreover, Klotho is essential for oligodendrocyte maturation and myelin integrity. ²⁷

Klotho protein expression in the hippocampus has been shown to decrease during aging. Secreted Klotho in CA1 area neurons positively affected object localization, passive avoidance memory performance, and improved object recognition. Overexpression of Klotho increased the initial enhancement of synaptic transmission in area CA1 and altered the parameters of synaptic transmission. ²⁸ Lower Mini-Mental State Examination scores were associated with low plasma Klotho levels. ²⁹ There are drugs that increase Klotho concentrations in the blood, some of which cross the blood-brain barrier. Increased Klotho levels have been reported with mTOR inhibitors (rapamycin, everolimus), inhibitors of the renin-angiotensin system (losartan, valsartan), pentoxifylline, statins (fluvastatin), and vitamin D. ³⁰

Nutritional factors affecting Klotho protein expression

Among others such as cerebrovascular diseases (which is known to be the most commonly reported risk factor), hypertension, obesity, physical activity, diabetes, diet is known to be a risk factor for AD. ³¹ Nowadays there is no diet dedicated especially to AD patients, but a lot of studies analyze which dietary elements have positive and negative influence on developing AD or how they influence on cognitive function. Not only deficiency but also surplus of dietary compounds have an impact, positive or negative, on developing AD. ³²

Impact of nutrition on Klotho protein expression

It was investigated that the level of Klotho protein decreases with age in humans, as a result cell death rate increases. ⁴⁷ Limiting of the Klotho protein amount was also observed in patients suffering from chronic kidney disease, AD, and diabetes. ⁴⁸ Some research proves that decreased concentration of Klotho protein in the serum correlates with higher mortality rate. ⁴⁹ What is interesting is that it is only accurate in patients with low levels of physical activity, because exercising alters this relation.

Klotho protein is said to be an AD-related protein. Co-receptor β-klotho binds to FGF21, which is a neuroprotective endocrine hormone. This combination is said to delay the onset of AD. ⁴⁶ Klotho protein is coded by the KL gene, which appears in 20% of patients in variant KL-VS. It consists of 6 missense variants, heterozygosity for KL-VS is connected with an increased amount of Klotho protein. ⁵⁰ Heterozygosity of KL-VS increases circulation of Klotho while carrying two variants decreases it. ⁴⁶ In research conducted by Belloy et al., ⁴⁶ it was investigated whether KL-VS variant reduces risk of amyloid deposits in patients who are APOE*4 carriers which do not have any cognitive decline. Investigation with PET proved that KL-VS variant reduces risk of amyloid accumulation, but only in APOE*4 carriers. These findings show the importance of focusing on the KL-VS variant in future studies. Especially in clinic trials, limiting group of APOE*4 to those without KL-VS variant. This would distinguish participants of clinical trials, with increased risk of amyloid deposition, before even their symptoms occur. This will support the creation of AD drug targets. ⁵¹

Dubal and Yokoyama ⁴⁹ conducted a high-powered meta-analysis including more than 20,000 individuals. Participants were above 60 years old and divided into different groups due to normal cognitive aging, mild cognitive impairment, and AD. They also proved that among APOE*4 carriers with KL-VS heterozygosity there is reduced risk for mild cognitive impairment or AD occurrence. What is interesting is that correlation was the strongest in the people between 60 and 80 years old. KL-VS homozygosity was connected with decreased Klotho levels and shorter life span. ⁴⁶

In the study conducted by Gaitán et al., ⁵⁰ it was observed that KL-VS carriers compared to non-carriers have higher serum and cerebrospinal fluid (CSF) Klotho levels. What is more, there was higher concentration in CSF than in serum, and women had higher Klotho CSF and serum concentration compared to men. It was also described that levels of Klotho in CSF are higher in younger people. ⁵²

Klotho protein exerts neuroprotective effects through multiple mechanisms, including modulation of insulin/insulin-like growth factor (IGF-1) signaling, oxidative stress reduction, enhancement of synaptic plasticity, and suppression of neuroinflammation. By acting as an endogenous inhibitor of IGF-1 signaling, Klotho enhances cellular stress resistance and mitigates Aβ accumulation and tau hyperphosphorylation, both key features of AD. Additionally, Klotho counteracts oxidative stress by upregulating antioxidant enzymes such as superoxide dismutase and catalase while inhibiting Nicotinamide Adenine Dinucleotide Phosphate (Reduced form) oxidase, thus protecting neurons from damage and supporting mitochondrial function.

Another critical role of Klotho is its impact on synaptic plasticity and cognitive function. It enhances long-term potentiation in the hippocampus and modulates N-Methyl-D-Aspartate receptor activity, improving glutamatergic neurotransmission and memory consolidation. Furthermore, Klotho exerts anti-inflammatory effects by inhibiting NF-κB signaling and reducing the production of pro-inflammatory cytokines like Tumor Necrosis Factor-α and IL-6, thereby preventing excessive microglial activation and synaptic dysfunction.

Through its combined actions in metabolic regulation, oxidative stress reduction, synaptic maintenance, and inflammation control, Klotho emerges as a crucial neuroprotective factor with potential therapeutic implications for AD. Future studies should explore strategies to enhance Klotho expression in the brain, either through pharmacological agents or lifestyle modifications, to maximize its neuroprotective potential.^53,54

Correlation between type of eaten food and the level of Klotho protein

It has been known for a long time that some types of diet have a beneficial impact on our health. Recent studies show that it also influences Klotho protein levels. Wu et al. ³⁴ investigated Klotho levels in 7906 people with four different dietary pattern: the Mediterranean, the low-carbohydrate-diet, a low-fat diet and a low-carbohydrate diet. The positive correlation occurred between the Mediterranean diet and Klotho levels. It was significant also considering different subgroups which differed with sex, age, or occurrence of obesity. ⁵⁵ The Mediterranean diet is rich in meat from fish, olive oil which is full of monounsaturated fats, fresh vegetables, fruits, whole grains, and moderate alcohol consumption. This diet is praised not only due to its beneficial role in cognitive decline, but it also reduces risk of cardiovascular diseases, diabetes, obesity, and some cancers like breast cancer or colorectal cancer. ⁵⁶ Wu et al. ³⁴ suggest that the Mediterranean diet has such a beneficial effect in the study compared to other dietary patterns because of the food synergy. This concept assumes to look at foods in general not as a single food component in order to gain further perspective. There are correlations between different food ingredients, and there are interactions between the food and human system. ⁵⁷

For example, a low-fat diet does not affect cholesterol level so much as a Mediterranean diet due to the fact that not only saturated and polyunsaturated fat affect serum cholesterol amount. ⁵⁸ What also distinguishes the Mediterranean diet from other dietary patterns is that there is a closer focus on food-based approach rather than nutrient-based. This allows us to observe complex metabolic correlations between the foods. ⁵⁴

Shafie et al. ⁵⁶ in the study revealed that high-protein and low-calorie diets increase Klotho protein levels in the mouse brains. The rats were divided into five groups according to the type of food they were eating for 10 weeks: high-fat food, low-calorie food, high-protein food, low-calorie and high-protein food, and a control group which was applied to normal food. Behavioral and molecular assessments revealed. Both high-protein diet and low-calorie diet improved their cognitive function, the best results were while adjusting high-protein and low-calorie diet. ⁵⁹

The research by Ostojic et al. ⁵⁷ showed that there are significant gender differences in Klotho level. Woman had higher serum level, and additionally, some food components like dietary fibers, phosphorus, and potassium consumed every day were resulting in higher Klotho levels but only in men. In this study, there were also two participants who were consuming high doses of alcohol every day, their Klotho protein levels were lower than in other people. ⁶⁰ The study conducted by Jurado-Fasoli and colleagues ⁵⁸ showed no significant associations between total energy intake with Klotho plasma levels. The only exception was a direct association between alcohol intake and Klotho protein serum levels in women. ⁶¹

Interestingly there was association among energy-adjusted carbohydrates/total sugars and Klotho protein levels. ⁶⁰ Similar results were observed in the study on animals. ⁶² This may be explained by regulatory features of Klotho protein. This molecule is involved in the glucose homeostasis as a part signaling pathway including insulin and IGF-1. ⁶³ IGF-1 may be responsible for Klotho protein upregulation as a response for higher dietary carbohydrates uptake. ⁶⁰ Villagomez et al. ⁶¹ investigated sugar sweetened beverage intake in young children and its correlation with serum Klotho. There was found a positive correlation between any consumption of sugar sweetened beverage and increase of Klotho level. Interestingly, the same study found the possibility of family stress and low socioeconomic status lead to the low serum Klotho level. ⁶⁴

Klotho protein is believed to be part of the controlling system of blood tension regulation via sodium reabsorption. It was observed that Klotho haplo-deficiency correlates with blood pressure elevation. There were also Klotho haplo-deficiency was connected with arterial stiffness and renal dysfunction.^65,66 Applying exogenous Klotho may increase blood pressure. Hu et al. ¹³ measured the influence of sodium levels on Klotho protein. High dietary salt intake resulted in a decrease of serum Klotho level and increased while low salt intake. ⁶⁷

The study by Wang et al. ⁶⁵ showed that everyday vitamin C consumption positively correlates with serum Klotho level. Another food element that influences Klotho level is resveratrol. This is one of the antioxidants. This is a natural polyphenol which occurs naturally in grapes and red wine. It is known for years from its beneficial role in fighting obesity, cardiovascular disease, obesity, and cancer. ⁵⁴ Recent discoveries show its anti-inflammatory features ⁶⁸ and its role in increasing Klotho protein level. Hsu et al. ⁶⁹ suggests that resveratrol increases renal Klotho expression due to enhancing transcription factors such as ATF3 and c-Jun, which belongs to activator protein 1 family. ⁶⁹ Those molecules are engaged in the cell lifespan regulation. ⁷⁰ What is more, Klotho promoter activity is reduced by excessive expression of p16 and p56 tumor suppressor proteins, ⁶⁸ while Peroxisome Proliferator-Activated Receptor-γ agonists or the epidermal growth factor indicate induction of Klotho transcription. ⁷¹ Resveratrol induces ATF3 and c-Jun mRNA as well as Sirt1 mRNA. Sirt-1 may enhance the induction effect of resveratrol on Klotho mRNA expression in a different way than ATF3 and c-Jun.^72–74

Interestingly, Klotho protein may also influence other molecules’ levels. For example, creatine uptake via upregulation of CT1 transporter. This transmembrane protein which transports creatine into target cells in sodium and chloride dependent mechanisms. ⁷⁵ Klotho protein leads to upregulation of creatine transporters by stabilizing the carrier in the membrane of the cell (Figure 2).^76–78

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Figure 2.

Types of dietary patterns which lead to changes of Klotho protein level.

Summary

Several reviews have examined the role of Klotho in aging and neurodegenerative diseases, primarily focusing on its genetic regulation, molecular mechanisms, and potential as a therapeutic target. These studies have largely emphasized Klotho's impact on oxidative stress, neuroinflammation, and synaptic function in AD. However, relatively few reviews have explored the influence of lifestyle factors, particularly diet, on Klotho expression and its implications for cognitive health. Given emerging evidence that certain dietary patterns and nutrients can modulate Klotho levels, this review aims to bridge that gap by analyzing the potential role of nutrition in regulating Klotho and its protective effects in AD. By synthesizing findings from recent studies on dietary modulation of Klotho, we provide a novel perspective on how nutrition-based interventions could complement existing therapeutic strategies for AD.

Current information suggests that Klotho protein has diverse functions, including a significant role in neurodegenerative diseases. Reduced plasma Klotho protein levels increase the risk of mortality due to normal aging. The presented review of scientific papers shows that reduced serum Klotho protein levels are associated with higher mortality. This occurs mainly among patients with low levels of physical activity, as exercise alters this relationship. Nowadays there is no diet dedicated especially to AD patients, but a lot of studies analyze which dietary elements have positive and negative influence on developing AD. It has been discovered that the types of dietary patterns that lead to an increase in Klotho protein levels are high intake of vitamin C, resveratrol, low salt intake, Mediterranean diet, high-protein and low-calorie diet, high-carbohydrate intake.