A meta-analysis of 22 cohorts seems to leave little doubt that variants of the longevity gene klotho protect against dementia—at least in people unfortunate enough to have inherited an ApoE4 allele. Researchers led by Michael Belloy, Stanford University, calculated that cognitively normal APOE4 carriers who are heterozygous for the F352V/C370S klotho haplotype are 35 percent less likely to develop mild cognitive impairment or AD. Published April 13 in JAMA Neurology, the study also supports the idea that Klotho VS slows accumulation of Aβ in the brain. “[The] meta-analysis provides strong evidence that individuals who carry APOE4 are not uniformly fated to develop AD,” noted Dena Dubal and Jennifer Yokoyama, University of California, San Francisco, in an accompanying editorial.

  • Analysis of more than 20,000 people says Klotho protects ApoE4 carriers.
  • The gene’s VS haplotype docks their risk of AD by up to a third.
  • Klotho VS associated with less amyloid burden in the brain.

APOE4 is the strongest genetic risk factor for sporadic, late-onset AD. Just recently, a separate paper in JAMA Neurology once again reinforced that ApoE4 genotype and family history of dementia were the principal determinants of amyloid pathology in healthy older people.

Klotho is named for the Greek goddesses who spins the threads of mythological life. The gene has puzzled scientists since it revealed itself to be involved in longevity in 1997. Its protein regulates biology in multiple organs, including the brain, where it seems to enhance learning and memory (May 2014 news). Klotho levels fall with age and in AD (Semba et al., 2014). Curiously, people who carry a single copy of the VS variant live longer than those with no or two copies (Arking et al., 2002). This is likely because heterozygotes have more klotho in their circulation. Higher levels have been tied not only to longevity but also to large cerebral cortex volume, strong functional connectivity, and better cognition (Yokoyama et al., 2015; Yokoyama et al., 2016; Dubal et al., 2014). 

Last year, Dubal and colleagues reported that the VS haplotype associated with lower amyloid burden among 127 healthy ApoE4 carriers in a cohort of 309 middle-aged adults in Wisconsin (Erickson et al., 2019). In Michael Greicius’ lab at Stanford, Belloy and colleagues use big-data approaches to learn what protects ApoE4 carriers against dementia. They wondered if this klotho/AD association would hold up in a larger sample.

Klotho Protects. Among older APOE4 carriers, klotho VS heterozygotes were 36 percent less likely to develop MCI or AD over three years. Protection seems to kick in around age 77. [Courtesy of Belloy et al., JAMA Neurology.]

Belloy examined data from 22 cohorts comprising 36,530 research volunteers in observational aging and AD cohorts. Of those, 22,748 fit the inclusion criteria. They came from Alzheimer’s disease centers, ADNI, NIA, Mayo Clinic, ROSMAP, and Washington University studies, to name a few. Belloy ran case-control comparisons and correlated longitudinal outcomes with klotho genotype.

In the case-control analysis, 26 percent of 11,576 ApoE4-negative volunteers carried one copy of the klotho VS haplotype. This percentage was the same regardless of AD diagnosis, suggesting the klotho haplotype had no bearing on the AD risk of people without the E4 allele.

Among the 9,240 ApoE4 carriers, however, it was a different story. Twenty-nine percent of the cognitively normal among them carried the VS allele versus 25.3 percent of those diagnosed with AD. This worked out to a risk ratio of 0.75 for AD among ApoE4-positive klotho VS carriers. This association was mainly driven by people between age 60 and 80, for whom the odds ratio was 0.69.

To test how klotho might push back dementia, Belloy and colleagues examined longitudinal data from the ADC, ADNI, and ROSMAP cohorts. Among 1,997 cognitively normal APOE4 carriers, klotho VS heterozygotes had a hazard ratio of 0.64 for developing mild cognitive impairment or AD over a period of three years compared with klotho homozygotes. Over five years, their HR was 0.6. Comparing hazard ratios by age suggested that the protection begins to kick in around age 77 (see figure above).

In people who already had MCI, klotho VS seemed less protective. The hazard ratio for incident AD among those with MCI was 0.8 over three years, and 0.75 over five years. “This suggests that the protective nature of KL-VS HET+ status is stronger in control participants and diminishes in affected individuals who have already developed MCI,” the authors wrote.

Klotho Reduces Amyloid. APOE4 carriers heterozygous for klotho VS have less amyloid in their brain. [Courtesy of Belloy et al. JAMA Neurology.]

How does the klotho variant protect? And why only in ApoE4 carriers? Belloy thinks this all ties in with amyloid burden. Similar to Dubal before, Belloy found that klotho VS came with higher CSF Aβ42, and lower uptake of amyloid PET tracers in accumulating regions, including parietal, temporal, frontal, and cingulate cortices. Belloy said klotho might protect ApoE4 carriers only because they are most at risk for amyloid deposition.

This would agree with newly published screening data from the A4 AD prevention trial. Writing in the April 6 JAMA Neurology, researchers led by Reisa Sperling at Brigham and Women’s Hospital, Boston, reported that among 4,486 volunteers aged 65 to 85, only ApoE4 genotype and a family history of dementia distinguished amyloid-positive from amyloid-negative participants. None of the other factors examined that are often associated with AD had any bearing on whether a person had amyloid in his or her brain. They included sex, level of education, marital status, and a range of lifestyle factors such as body mass index, physical activity, hours of sleep, alcohol and caffeine consumption, and tobacco use. “These risk factors for AD dementia may play a role in the vulnerability/resilience to cognitive decline in the setting of elevated Aβ rather than serving as a risk factor for Aβ accumulation itself,” Sperling and colleagues write.

Another reason why klotho VS may only protect ApoE4 carriers is because the latter is an anti-aging factor. “If you have ApoE4 you will likely not live as long,” said Belloy. He thinks klotho, being a longevity factor, might counteract that.

Both the aging and amyloid hypotheses need to be functionally validated, he said.

One approach would be to correlate Aβ and dementia with blood levels of klotho. Belloy said this was beyond the scope of the current study, something Dubal and Yokoyama lamented. “The lack of measurements of the klotho hormone itself from the serum or cerebrospinal fluid of individuals restricts interpretation of the findings, particularly since klotho levels might represent a higher resolution biomarker in assessing the APOE4-AD risk,” they write. Belloy has serum tests in his sights. “If klotho levels do correlate, that would bring us a new biomarker and potentially a new therapeutic target for AD,” he said.—Tom Fagan

Comments

  1. This is an interesting study by Belloy and colleagues, which reports an association between Klotho-VS heterozygosity (KL-VS HET+) and apolipoprotein 4 (APOE4) allele carriage, with risk for conversion to Alzheimer’s disease (AD) and β-amyloid (Aβ) pathology. Specifically, they report that in APOE4 carriers, those who were KL-VS HET+ showed a reduced risk of converting to AD, higher CSF Aβ, and lower PET Aβ when compared to KL-VS HET-. The results presented in this study add to the growing literature supporting the hypothesis that multiple gene variants are likely to interact to influence disease outcomes in AD.

    The main strength of this study is the size and quality of the sample, with participant data available from a number of large longitudinal cohort studies. As discussed by Belloy et al., we have previously investigated whether the interaction between APOE4 and KL-VS is associated with cognitive decline in the Australian Imaging, Biomarker, and Lifestyle (AIBL) study (Porter et al., 2019). We observed no difference in cognitive decline over 7.5 years between KL-VS HET+/HET- in cognitively normal APOE4 carriers and regardless of PET Aβ burden. However, as calculated by Belloy et al., in our sample there is an association between KL-VS, APOE4, and PET Aβ burden in cognitively normal APOE4 carriers, with odds ratios observed similar to those of the current study. Whilst our initial study, referenced here, did not report any influence of KL-VS on cognitive decline, our subsequent studies assessing it in combination with an increased number of genetic variants do report an effect of KL-VS. In our published genetic risk profile (Porter et al., 2018) and episodic memory weighted genetic risk scores (Porter et al., 2018), KL-VS status significantly contributed to the prediction of cognitive performance.

    Overall, Belloy and colleagues’ study is an important one that adds to the growing literature indicating that genetic influence over progression to Alzheimer’s disease is more than just APOE4 alone. Lastly, we strongly agree with the authors’ suggestion that KL-VS genotype be seriously considered in the selection of participants in prevention trials, to increase the likelihood the cohort will convert to AD, and further, as additional genetic variants are assessed in this way that they be similarly considered.

    References:

    . Klotho allele status is not associated with Aβ and APOE ε4-related cognitive decline in preclinical Alzheimer's disease. Neurobiol Aging. 2019 Apr;76:162-165. Epub 2019 Jan 6 PubMed.

    . Cognitive gene risk profile for the prediction of cognitive decline in presymptomatic Alzheimer’s disease. Personalized Medicine in Psychiatry, March–April 2018

    . A Polygenic Risk Score Derived From Episodic Memory Weighted Genetic Variants Is Associated With Cognitive Decline in Preclinical Alzheimer's Disease. Front Aging Neurosci. 2018;10:423. Epub 2018 Dec 19 PubMed.

  2. This is a very extensive meta-analysis of over 20,000 individuals, aimed at elucidating whether an interaction between APOE4 and a polymorphism in the coding region of the klotho gene, known as KL-VS, affects AD outcome. The genotype KL-VSHET+ was associated with reduced risk for AD in individuals carrying APOE4 who were 60 years old or older; control participants carrying APOE4 with KL-VS heterozygosity were at reduced risk of converting to MCI or AD and in control participants who carried APOE4 and were aged 60 to 80 years, KL-VS heterozygosity was associated with higher Aβ in CSF and lower Aβ on PET scans.

    These are very interesting findings which serve as additional validation for the previously published work on the neuroprotective role of klotho. In the past we showed that klotho levels decrease as a function of age in the healthy brain (Duce et al., 2008). We then provided evidence for its protective functions in the CNS and reported possible mechanisms of protection: a reduction in oxidative stress (Zeldich et al., 2014), increased oligodendrocyte differentiation and myelination in vitro and in vivo (Chen et al., 2013; Zeldich, 2015), improved cognition and LTP in an APP model overexpressing klotho (Dubal et al., 2015), and reduced cell death and neuroinflammation in an ALS mouse model (Zeldich et al., 2019). In other words, klotho functions against the common age-related changes that occur in the brain during normal aging and neurodegeneration: it is anti-oxidative, anti-inflammatory, and promotes myelination.

    We and others also showed that being heterozygous for KL-VS, a double mutation associated with higher levels of klotho, is beneficial for cognition and in a multitude of diseases (Dubal et al., 2014). In addition to the benefits due to the higher level of Klotho, we pointed out a biochemical mechanism specific to KL-VS that may explain its effects (Tucker-Zhou et al., 2013). 

    Among the key questions to consider addressing in the future are:

    1. What functions among those described for klotho may interact differently with APOE4 and APOE3?
    2. Is it the anti-inflammatory action of klotho that may affect microglia behavior into phagocytosing Aβ? APOE was recently shown to affect AD in part through its immunomodulatory function. This function of APOE is likely linked to triggering receptor expressed on myeloid cells 2 (TREM2), which is expressed by microglia in the CNS (Shi and Holzman, 2018). 
    3. Or, is it the anti-oxidative role of klotho which precludes chemical modifications in Aβ? Oxidation would make Aβ more insoluble and resistant to degradation.
    4. Regarding the conversion from MCI to AD, does KL-VS prevent white-matter abnormalities which may affect cognition via some indirect or direct lipid interaction with APOE4?
    5. Why do individuals over 80 not benefit from klotho heterozygocity like those aged 60 to 80? I propose that a potential reason is lower levels of klotho as we described to occur with aging. Perhaps under a certain threshold of klotho levels, it is no longer beneficial.
    6. There is an excellent ELISA kit for measuring human klotho levels in blood or CSF. It would be interesting to quantify klotho levels in a subgroup of control, MCI, and AD individuals with KL-VS with APOE4 and APOE3. If klotho levels are similar in APOE4 and 3 carriers, perhaps the modifications caused by the two amino acid substitutions in KL-VS could explain the intriguing interplay between klotho and APOE4.

    Last but not least, this work emphasizes the importance of identifying compounds that boost klotho levels and might delay or even prevent AD.

    References:

    . Gene profile analysis implicates Klotho as an important contributor to aging changes in brain white matter of the rhesus monkey. Glia. 2008 Jan 1;56(1):106-17. PubMed.

    . The antiaging protein Klotho enhances oligodendrocyte maturation and myelination of the CNS. J Neurosci. 2013 Jan 30;33(5):1927-39. PubMed.

    . Biochemical and functional characterization of the klotho-VS polymorphism implicated in aging and disease risk. J Biol Chem. 2013 Dec 20;288(51):36302-11. Epub 2013 Nov 11 PubMed.

    . Life extension factor klotho enhances cognition. Cell Rep. 2014 May 22;7(4):1065-76. Epub 2014 May 10 PubMed.

    . The neuroprotective effect of Klotho is mediated via regulation of members of the redox system. J Biol Chem. 2014 Aug 29;289(35):24700-15. Epub 2014 Jul 18 PubMed.

    . The Anti-Aging Protein Klotho Enhances Remyelination Following Cuprizone-Induced Demyelination. J Mol Neurosci. 2015 Oct;57(2):185-96. Epub 2015 Jun 12 PubMed.

    . Life extension factor klotho prevents mortality and enhances cognition in hAPP transgenic mice. J Neurosci. 2015 Feb 11;35(6):2358-71. PubMed.

    . Interplay between innate immunity and Alzheimer disease: APOE and TREM2 in the spotlight. Nat Rev Immunol. 2018 Dec;18(12):759-772. PubMed.

    . Klotho Is Neuroprotective in the Superoxide Dismutase (SOD1G93A) Mouse Model of ALS. J Mol Neurosci. 2019 Oct;69(2):264-285. Epub 2019 Jun 27 PubMed.

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References

News Citations

  1. Longevity Gene Boosts Brainpower, Even in the Young

Paper Citations

  1. . Klotho in the cerebrospinal fluid of adults with and without Alzheimer's disease. Neurosci Lett. 2014 Jan 13;558:37-40. Epub 2013 Nov 7 PubMed.
  2. . Association of human aging with a functional variant of klotho. Proc Natl Acad Sci U S A. 2002 Jan 22;99(2):856-61. Epub 2002 Jan 15 PubMed.
  3. . Variation in longevity gene KLOTHO is associated with greater cortical volumes. Ann Clin Transl Neurol. 2015 Mar;2(3):215-30. Epub 2015 Jan 26 PubMed.
  4. . Systemic klotho is associated with KLOTHO variation and predicts intrinsic cortical connectivity in healthy human aging. Brain Imaging Behav. 2016 Oct 6; PubMed.
  5. . Life extension factor klotho enhances cognition. Cell Rep. 2014 May 22;7(4):1065-76. Epub 2014 May 10 PubMed.
  6. . KLOTHO heterozygosity attenuates APOE4-related amyloid burden in preclinical AD. Neurology. 2019 Apr 16;92(16):e1878-e1889. Epub 2019 Mar 13 PubMed.

Further Reading

No Available Further Reading

Primary Papers

  1. . Association of Klotho-VS Heterozygosity With Risk of Alzheimer Disease in Individuals Who Carry APOE4. JAMA Neurol. 2020 Apr 13; PubMed.
  2. . Association of Factors With Elevated Amyloid Burden in Clinically Normal Older Individuals. JAMA Neurol. 2020 Apr 6; PubMed.