Klotho: The Ageing-Suppressor Gene

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Klotho The Ageing-Suppressor Gene

• By
• Naglaa Fathy Alhusseini
• Assistant prof. of Medical Biochemistry
• Faculty of Medicine
• Benha University
• 2013

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Overview

• Introduction
• Klotho-deficient mice
• Klotho-overexpressing transgenic mice
• Klotho protein functions
• Conclusions

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Introduction

• Klotho
• in Greek mythology, three goddesses determine
  life span of every one by controlling the thread
  of life. They are Klotho, Lachesis, and Atropos
  who spins, measures, and cuts the thread of life,
  respectively.

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• Control the life (spins the thread of life) and
  destiny of everyone
• She is the goddess who helps life to unfold, in
  contrast to The (apoptotic) Atropos, who cuts the
  thread of life

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Introduction

• Gene
• Identified app. 16 years ago, by the Japanese
  group of Kuro-o et al.
• Named after Greek goddess,As prolonging lifespan
  is probably the most important role of this
  ageing-suppressor gene
• The klotho gene is composed of 5 exons
• The klotho gene is expressed in limited tissues
  and cell types. The highest expression is
  observed in distal convoluted tubules in the
  kidney and choroid plexus in the brain .
• Lower expression is detected in pituitary gland,
  brain, parathyroid gland pancreas, ovary, testis,
  placenta, skeletal muscle, urinary bladder, colon
  , inner ear , and breast epithelial cells

Nature 1997 390 4551
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Introduction

• Japanese researchers reported
• Defect in Klotho gene expression in the mouse
  resulted in a syndrome that resembled
• Human ageing, including
• Short lifespan, infertility, arteriosclerosis,
  skin atrophy, osteoporosis and emphysema
• The gene encoded a membrane protein that
• Shared sequence similarity with the
  beta-glucosidase enzymes

Nature 1997 390 4551
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Klotho- deficient mice
7-week-old normal mouse (left) and a klotho
mouse, an animal model that shows multiple
phenotypes resembling human aging
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Ageing Research Reviews 200984351
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Ageing Research Reviews 200984351
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Introduction

• The Klotho gene encodes
• Single-pass transmembrane protein
• Belongs to a family 1 glycosidase
• Expressed primarily in renal tubules (distal
  tubules)
• Present in the circulation and urine

Blood Cells Mol Dis 1998 24 83100
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• Klotho-deficient mice and FGF23-deficient mice
  have an identical phenotype including
• Hyperphosphataemia, hypercalcaemia, elevated
  plasma calcitriol and vascular calcification, in
  addition to premature ageing
• In contrast, over-expression of the Klotho gene
• Extends the lifespan and increases resistance to
  oxidative stress

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Regulation of FGF23 signaling by Klotho

• The common phenotypes of Klotho and FGF23
  overexpression and deletion, respectively, led to
  the postulate of a
• Common signal transduction pathway
• Kuro et al. showed that
• Klotho protein directly bound to multiple FGFRs
• The KlothoFGFR complex bound to FGF23 with
  higher affinity than FGFR or Klotho alone

J Biol Chem 2006 281 61206123
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Regulation of FGF23 signaling by Klotho

• Conversion by Klotho of canonical FGF receptor
  into FGF23-specific receptor

Nephrol Dial Transplant 2007 22 15241526
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Regulation of FGF23 signaling by Klotho

• The fact that FGF23 requires Klotho as a
  co-receptor explains
• Why Klotho-deficient mice develop phenotypes
  identical with those observed in FGF23-deficient
  mice and
• Why Klotho-deficient mice had extremely high
  serum FGF23 levels

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Function of the transmembrane form of Klotho

• 1- Regulation of phosphate metabolism
• Recent studies have identified FGF23 as a novel
  endocrine factor that lowers blood phosphate and
  vitamin D levels .
• FGF23 is secreted from osteocytes in response to
  high blood phosphate and vitamin D levels . FGF23
  acts on kidney to induce phosphaturia .
• FGF23 induces a negative phosphate balance by
  functioning as a phosphaturic hormone as well as
  a counter-regulatory hormone for vitamin D
• Kuro-o 2009, Klotho and aging NIH

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Function of the secreted form of Klotho

• 1- Suppression of insulin/IGF-1 signaling
• Klotho-deficient mice are hypoglycemic and
  extremely sensitive to insulin. In contrast,
  Klotho-overexpressing transgenic mice are
  moderately resistant to insulin and IGF-1,
  although they maintain normal fasting blood
  glucose levels and are not diabetic.
• These observations suggest that Klotho may
  inhibit the insulin/IGF-1 signaling pathway.
• The ability of Klotho to inhibit insulin/IGF-1
  signaling may be associated with anti-aging
  properties of Klotho, since numerous lines of
  genetic evidence indicate that moderate
  inhibition of insulin-like signaling pathway is
  one of the evolutionarily conserved mechanisms
  for suppressing aging
• Kuro-o 2009, Klotho and aging NIH

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• 2- Suppression of oxidative stress
• Activation of insulin/IGF-1 signaling increases
  activity of a serine-threonine kinase, which
  inactivate the transcription factors FOXOs
  (up-regulate expression of multiple target genes,
  including antioxidant enzymes such as catalase
  and mitochondrial manganese-superoxide dismutase
  (SOD2) .
• Catalase and SOD2 detoxify harmful reactive
  oxygen species (ROS) hydrogen peroxide and
  superoxide, respectively, and reduce oxidative
  stress.
• Thus, activation of FOXOs by inhibiting
  insulin/IGF-1 signaling can increase cellular
  protection against oxidative stress and may
  contribute to the suppression of aging.

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• 3- Nitric oxide production
• Klotho deficiency causes a reduction of NO
  synthesis in vascular endothelial cells.
• Consistent with this finding, Klotho-deficient
  mice exhibit impaired angiogenesis, which is
  dependent on endothelium-derived NO

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• 4- Klotho as a suppressor of breast cancer
• clinical and laboratory data indicate a critical
  role for insulin/IGF-1 signaling in breast
  cancer. Notably
• 1) increased serum insulin levels are associated
  with adverse prognosis in breast cancer
• 2) High circulating IGF-1 levels are associated
  with increased risk of pre-menopausal breast
  cancer and
• 3) Inhibition of insulin/IGF-1 signaling inhibits
  growth of breast cancer cells.
• Since secreted Klotho protein inhibits
  activation of insulin/IGF-1 receptors, Klotho may
  function as a suppressor of breast cancer.
• Kuro-o 2009, Klotho and aging NIH

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• In addition, several lines of experimental
  evidence support the notion that Klotho functions
  as a tumor suppressor.
• 1) Forced expression of Klotho in breast cancer
  cell lines reduces their proliferation.
• Inhibition of IGF-1 signaling by Klotho
  increased expression of CCAAT/enhancer-binding
  proteins (C/EBP)
• Klotho may be a suppressor of breast cancer. It
  remains to be determined whether the anti-breast
  cancer activity of Klotho depends primarily on
  its ability to suppress IGF-1 signaling or on
  other unknown mechanisms.

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• Defects in Klotho expression can lead to
  underexpression of FGF23 and accumulation of
  phosphates.  Accumulated phosphates can
  accelerate aging.  Phosphate retention can lead
  to an aging phenotype.
• FGF23 and its relationship to Klotho are linked
  to a number of bone and joint diseases.
• Klotho is a regulator of oxidative stress and
  cell senescence.
• Klotho inhibits growth and promotes apoptosis in
  some cancer lines.
• Klotho protein protects against endothelial
  dysfunction and hypertension.

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• Control of Klotho expression comes about through
  epigenetic mechanisms some cancers can silence
  Klotho expression.
• Consuming cola drinks rich in phosphoric acid
  when coupled with Klotho insufficiency may exert
  a pro-aging effect.
• In humans, studies suggest that Klotho KL-VS gene
  polymorphisms may be associated with stroke,
  coronary artery disease and longevity.
• Klotho pathways might be targets for anti-aging
  interventions.

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Human KLOTHO gene polymorphism and mutations

• . A functional variant of human Klotho protein
  contains six sequence variations .
• Interestingly, heterozygotes for this variant
  have advantage for longevity, while homozygotes
  are disadvantageous for survival, because
  homozygotes are significantly under-represented
  in the aged. In contrast, heterozygotes have
  longer life span than wild-types in multiple
  populations, suggesting that the KLOTHO gene
  variation affects human life span.
• Kuro-o 2009, Klotho and aging NIH

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• In addition, homozygosity of this variant is
  associated with traditional cardiovascular risk
  factors including low high-density lipoprotein
  cholesterol and high systolic blood pressure and
  newly identified as an independent risk factor
  for stroke and early-onset coronary artery
  disease.
• In contrast, heterozygosity is associated with
  lower risk for stroke and coronary artery
  disease, which is consistent with its association
  with long life span. In addition to this KLOTHO
  variant, several single-nucleotide polymorphisms
  (SNPs) are associated with bone mineral density
  glucose metabolism and cognitive function

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Additional observations gleaned from more-recent
publications

• Low levels of Klotho may serve as an early
  warning biomarker for kidney disease and
  cardiovascular complications
• Klotho suppresses renal fibrosis.
• inflammatory cytokines, such as TWEAK and TNFa,
  downregulate Klotho expression through an
  NF?B-dependent mechanism. These results may
  partially explain the relationship between
  inflammation and diseases characterized by
  accelerated aging of organs, including CKD.

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Klotho expression can be modulated by
dehydration.

• Some observations disclose a powerful effect of
  dehydration on decrease Klotho expression, an
  effect at least partially mediated by enhanced
  release of ADH and aldosterone.  

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Klotho as a tumor suppressor gene

• Epigenetic silencing of the tumor suppressor
  klotho in human breast cancer , Cancer colon and
  gastric cancer

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Age-related decline in Klotho may be related to
promoter methylation.

• methylation of the promoter can decrease gene
  transcription. These results provide evidence
  that changes in KL gene expression with age may,
  at least in part, be the result of epigenetic
  changes to the 5' regulatory region.

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Conclusions

• The discovery of the klotho gene has led to
  identification of multiple novel endocrine axes
  mediated by endocrine FGFs and Klothos that
  regulates various metabolic processes.
• The transmembrane form of Klotho protein
  functions as a co-receptor for FGF23 and
  regulates phosphate, calcium, and vitamin D
  metabolism.
• The extracellular domain of Klotho protein is
  shed and secreted into the systemic circulation
  where it functions as an endocrine factor. The
  secreted Klotho protein controls multiple ion
  channels and growth factor signaling pathways
  including insulin, IGF-1.

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Conclusions

• potentially participating in biology of cancer
  and stem cells. Identification of the common
  molecular basis for these multiple function of
  Klotho will be of particular importance to
  understand the anti-aging properties of Klotho.

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Thank You!