Phosphate as an Agent of Accelerated Aging
Here find an interesting viewpoint on the role of phosphate in mammalian biochemistry, suggesting that it tilts the playing field in the direction of faster degenerative aging. This emerges from work on the longevity-associated gene klotho and its effects on kidney function and vascular function in aging. As is usually the case in such matters, there is no great debate over whether or not specific mechanisms and contributions to aging and age-related diseases exist. The question is whether or not the size of the effect is large enough to care about, and that is always much harder to answer, given the immense complexity of cellular biochemistry.
During the evolution of skeletons, terrestrial vertebrates acquired strong bones made of calcium-phosphate. By keeping the extracellular fluid in a supersaturated condition regarding calcium and phosphate ions, they created the bone when and where they wanted simply by providing a cue for precipitation. To secure this strategy, they acquired a novel endocrine system to strictly control the extracellular phosphate concentration. In response to phosphate intake, fibroblast growth factor-23 (FGF23) is secreted from the bone and acts on the kidney through binding to its receptor Klotho to increase urinary phosphate excretion, thereby maintaining phosphate homeostasis.
The FGF23-Klotho endocrine system, when disrupted in mice, results in hyperphosphatemia and vascular calcification. Besides, mice lacking Klotho or FGF23 suffer from complex aging-like phenotypes, which are alleviated by placing them on a low-phosphate diet, indicating that phosphate is primarily responsible for the accelerated aging. Phosphate acquires the ability to induce cell damage and inflammation when precipitated with calcium. In the blood, calcium-phosphate crystals are adsorbed by serum protein fetuin-A and prevented from growing into large precipitates. Consequently, nanoparticles that comprised calcium-phosphate crystals and fetuin-A, termed calciprotein particles (CPPs), are generated and dispersed as colloids.
CPPs increase in the blood with an increase in serum phosphate and age. Circulating CPP levels correlate positively with vascular stiffness and chronic non-infectious inflammation, raising the possibility that CPPs may be an endogenous pro-aging factor. Terrestrial vertebrates with the bone made of calcium-phosphate may be destined to age due to calcium-phosphate in the blood.