Function
The physiological function of Lp(a)/apo(a) is still unknown. A function within the coagulation system seems plausible, given the aspect of the high homology between apo(a) and plasminogen. In fact, the LPA gene derives from a duplication of the plasminogen gene.
Other functions have been related to recruitment of inflammatory cells through interaction with Mac-1 integrin, angiogenesis, and wound healing.
However, individuals without Lp(a) or with very low Lp(a) levels seem to be healthy. Thus plasma Lp(a) is certainly not vital, at least under normal environmental conditions. Since apo(a)/Lp(a) derived rather recently in mammalian evolution - only old world monkeys and humans have been shown to harbour Lp(a) - its function might not be vital but just evolutionarily advantageous under certain environmental conditions, e.g. in case of exposure to certain infectious diseases.
Another possibility, suggested by Linus Pauling, is that Lp(a) is a primate adaptation to L-gulonolactone oxidase (GULO) deficiency, who thought that found only in certain lines of mammals. GULO is required for converting glucose to ascorbic acid (vitamin C), which is needed to repair arteries; following the loss of GULO, those primates that adopted diets less abundant in vitamin C may have used Lp(a) as an ascorbic-acid surrogate to repair arterial walls.
Read more about this topic: Lipoprotein(a)
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