The October 2009 blog entry Klotho anti-aging gene in the news describes how the Klotho protein exhibits anti-aging effects in mice when over-expressed and accelerates aging when under-expressed, Klotho’s role with respect to the vitamin D receptor (VDR), and how defects in Klotho expression is correlated with a number of disease processes. I said “As to how Klotho may impact on longevity: a) I have already mentioned its actions in averting tissue glycation, b) the IGF-1 pathway (affected by Klotho) has long been known to be associated with longevity and is that affected by calorie restriction, and c) Klotho promotes the body’s antioxidant defenses.” Research published in the last year reveals an important new link of Klotho to longevity involving phosphate clearance. I discuss that link and possible implications for consummate drinkers of cola drinks in this blog entry. Also, increasing evidence exists that Klotho functions as tumor suppressor, and I also discuss that topic.
Defects in Klotho expression can lead to underexpression of FGF23 and accumulation of phosphates
The 2010 paper Klotho introduces the main topic of this blog entry: “The klotho gene was identified as an “aging-suppressor” gene in mice that accelerates aging when disrupted and extends life span when overexpressed. It encodes a single-pass transmembrane protein and is expressed primarily in renal tubules. The extracellular domain of Klotho protein is secreted into blood and urine by ectodomain shedding. The two forms of Klotho protein, membrane Klotho and secreted Klotho, exert distinct functions. Membrane Klotho forms a complex with fibroblast growth factor (FGF) receptors and functions as an obligate co-receptor for FGF23, a bone-derived hormone that induces phosphate excretion into urine. Mice lacking Klotho or FGF23 not only exhibit phosphate retention but also display a premature-aging syndrome, revealing an unexpected link between phosphate metabolism and aging.”
The link between Klotho, phosphate retention and aging was telegraphed in the October 2009 paper Klotho and aging. “The klotho gene encodes a single-pass transmembrane protein that forms a complex with multiple fibroblast growth factor (FGF) receptors and functions as an obligatory co-receptor for FGF23, a bone-derived hormone that induces negative phosphate balance. Defects in either Klotho or Fgf23 gene expression cause not only phosphate retention but also a premature-aging syndrome in mice, unveiling a potential link between phosphate metabolism and aging.”
The 2010 review Klotho as a regulator of fibroblast growth factor signaling and phosphate/calcium metabolism also describes the situation. “PURPOSE OF REVIEW: This review summarizes the most recent findings on Klotho in the regulation of fibroblast growth factor-23 (FGF23) signaling and phosphate/calcium homeostasis. — RECENT FINDINGS: The klotho gene encodes a single-pass transmembrane protein and functions as an aging-suppressor gene, which extends life span when overexpressed and accelerates the development of aging-like phenotypes when disrupted in mice. FGF23 is a hormone that suppresses phosphate reabsorption in renal proximal tubules. Recent studies have shown that Klotho mice and Fgf23 mice exhibit identical phenotypes including hyperphosphatemia and hypercalcemia in addition to the aging-like syndrome. This may be explained by the fact that Klotho binds to multiple FGF receptors and increases their affinity to FGF23.”
The mechanism of operation of Klotho with respect to FGF23 is further detailed in the 2010 publication Regulation of ion channels by secreted Klotho: mechanisms and implications. “Klotho is an anti-aging protein predominantly expressed in the kidney, parathyroid glands, and choroid plexus of the brain. It is a single-pass transmembrane protein with a large extracellular domain. The extracellular domain of Klotho is cleaved and released into extracellular fluid, including blood, urine, and cerebrospinal fluid. The membrane-bound full-length Klotho and secreted extracellular domain of Klotho have distinct functions. Membrane Klotho interacts with fibroblast growth factor (FGF) receptors to form high-affinity receptors for FGF23. Secreted Klotho functions as a humoral factor that regulates several ion channels and transporters, and other processes, including insulin and insulin-like growth factor signaling.”
FGF23 and its relationship to Klotho are linked to a number of bone and joint diseases, such as described in the 2010 publication [Bone and joint diseases in children. Phosphaturic hormone, FGF23, and bone metabolism]. “Fibroblast growth factor 23 (FGF23) belongs to FGF19 subfamily, whose members function like endocrine factors, and has a phosphaturic effect, leading to hypophosphatemia associated with rickets or osteomalacia when its concentration in blood is elevated. FGF23 is involved in the pathogenesis in many forms of hypophosphatemia including the autosomal dominant and recessive types, the X-linked type and the tumor-induced type. Alpha klotho, originally discovered as an anti-aging factor, along with the FGF receptor type 1 makes a specific receptor for FGF23.”
Accumulated phosphates can accelerate aging
The link between accumulated phosphates and aging is detailed in the 2010 publication Dietary and genetic evidence for phosphate toxicity accelerating mammalian aging. “Identifying factors that accelerate the aging process can provide important therapeutic targets for slowing down this process. Misregulation of phosphate homeostasis has been noted in various skeletal, cardiac, and renal diseases, but the exact role of phosphate toxicity in mammalian aging is not clearly defined. Phosphate is widely distributed in the body and is involved in cell signaling, energy metabolism, nucleic acid synthesis, and the maintenance of acid-base balance by urinary buffering. In this study, we used an in vivo genetic approach to determine the role of phosphate toxicity in mammalian aging. Klotho-knockout mice (klotho(-/-)) have a short life span and show numerous physical, biochemical, and morphological features consistent with premature aging, including kyphosis, uncoordinated movement, hypogonadism, infertility, severe skeletal muscle wasting, emphysema, and osteopenia, as well as generalized atrophy of the skin, intestine, thymus, and spleen. Molecular and biochemical analyses suggest that increased renal activity of sodium-phosphate cotransporters (NaPi2a) leads to severe hyperphosphatemia in klotho(-/-) mice. Genetically reducing serum phosphate levels in klotho(-/-) mice by generating a NaPi2a and klotho double-knockout (NaPi2a(-/-)/klotho(-/-)) strain resulted in amelioration of premature aging-like features. The NaPi2a(-/-)/klotho(-/-) double-knockout mice regained reproductive ability, recovered their body weight, reduced their organ atrophy, and suppressed ectopic calcifications, with the resulting effect being prolonged survival. More important, when hyperphosphatemia was induced in NaPi2a(-/-)/klotho(-/-) mice by feeding with a high-phosphate diet, premature aging-like features reappeared, clearly suggesting that phosphate toxicity is the main cause of premature aging in klotho(-/-) mice. The results of our dietary and genetic manipulation studies provide in vivo evidence for phosphate toxicity accelerating the aging process and suggest a novel role for phosphate in mammalian aging.”
Other effects of Klotho
Of course Klotho does other things beyond binding to FGF23 as outlined in my earlier blog entry and in the 2008 paper Klotho as a regulator of oxidative stress and senescence. “The klotho gene encodes a single-pass transmembrane protein that binds to multiple fibroblast growth factor (FGF) receptors and functions as a co-receptor for FGF23, a bone-derived hormone that suppresses phosphate reabsorption and vitamin D biosynthesis in the kidney. In addition, the extracellular domain of Klotho protein is shed and secreted, potentially functioning as a humoral factor. The secreted Klotho protein can regulate multiple growth factor signaling pathways, including insulin/IGF-1 and Wnt, and the activity of multiple ion channels. Klotho protein also protects cells and tissues from oxidative stress, yet the precise mechanism underlying these activities remains to be determined. Thus, understanding of Klotho protein function is expected to provide new insights into the molecular basis for aging, phosphate/vitamin D metabolism, cancer and stem cell biology.”
Klotho and cancer processes
The 2010 publication Klotho inhibits growth and promotes apoptosis in human lung cancer cell line is one of several dealing with the anti-cancer properties of Klotho. “Recently, published studies suggest that klotho can also serve as a potential tumor suppressor. The aim of this study is to investigate the effects and possible mechanisms of action of klotho in human lung cancer cell line A549. — CONCLUSIONS: Klotho can inhibit proliferation and increase apoptosis of A549 cells, this may be partly due to the inhibition of IGF-1/insulin pathways and involving regulating the expression of the apoptosis-related g nes bax/bcl-2. Thus, klotho can serve as a potential tumor suppressor in A549 cells.”
The 2010 publication The anti-aging gene KLOTHO is a novel target for epigenetic silencing in human cervical carcinoma suggests that turning the Klotho gene off by means of epigenetic silencing may be an important survival strategy used by certain cancers. “Recently, KLOTHO was reported to function as a secreted Wnt antagonist and as a tumor suppressor. Epigenetic gene silencing of secreted Wnt antagonists is considered a common event in a wide range of human malignancies. Abnormal activation of the canonical Wnt pathway due to epigenetic deregulation of Wnt antagonists is thought to play a crucial role in cervical tumorigenesis. In this study, we examined epigenetic silencing of KLOTHO in human cervical carcinoma. — Methylation-specific PCR and bisulfite genomic sequencing analysis of the promoter region of KLOTHO revealed CpG hypermethylation in non-KLOTHO-expressing cervical cancer cell lines and in 41% (9/22) of invasive carcinoma cases. Histone deacetylation was also found to be the major epigenetic silencing mechanism for KLOTHO in the SiHa cell line. — CONCLUSIONS: Epigenetic silencing of KLOTHO may occur during the late phase of cervical tumorigenesis, and consequent functional loss of KLOTHO as the secreted Wnt antagonist may contribute to aberrant activation of the canonical Wnt pathway in cervical carcinoma.”
Statins promote expression of Klotho
Finally, I hearken back to a 2004 publication which suggests that use of statins promotes Klotho expression, HMG-CoA reductase inhibitors up-regulate anti-aging klotho mRNA via RhoA inactivation in IMCD3 cells. The conclusion is “Statins inactivate the RhoA pathway, resulting in overexpression of klotho mRNA, which may contribute to the novel pleiotropic effects of statins towards vascular protection.” Other substances may also activate the expression of Klotho, but discovering them will take more research on my part.
Soft drinks, phosphoric acid and aging
Sixteen years ago, I would head down the corridor in my software company twice or three times a day to the vending machine for a diet coke. I loved the stuff and I still like its taste and short-term impact on me. And I love diet Dr. Pepper for the same reason too. Back then, little did I think I might be pursuing a pro-aging strategy. These and some other soft drinks are strong sources of phosphoric acid, a species of phosphates. If the above-described research is correct, and if I did not have strong Klotho expression to activate FGF23 to clear the phosphates out, accelerated aging could well have been a consequence of my soft drink addiction.
There has been serious questions posed as to whether consistent consumption of diet colas leads to osteoporosis(ref). “New research indicates that there may be more to the soda and osteoporosis connection than simply replacing the good stuff with the useless stuff. — Researchers at Tufts University, studying several thousand men and women, found that women who regularly drank cola-based sodas — three or more a day — had almost 4% lower bone mineral density in the hip, even though researchers controlled for calcium and vitamin D intake. But women who drank non-cola soft drinks, like Sprite or Mountain Dew, didn’t appear to have lower bone density. Soda and Osteoporosis: Possible Culprits. — Phosphoric acid, a major component in most sodas, may be to blame, according to lead study author Katherine Tucker, PhD. — Phosphorus itself is an important bone mineral. But if you’re getting a disproportionate amount of phosphorus compared to the amount of calcium you’re getting, that could lead to bone loss.”
Now to that concern I add another based on the research cited here. Is loading up on phosphoric acid due to frequent drinking of cola sodas robbing of longevity? And If there is a life-shortening effect due to chronic ingestion of drinks containing phosphoric acid, does it apply to everybody or only to people with defective Klotho or FGF23 expression?