Tissue-Nonspecific Alkaline Phosphatase in the Developing Brain and in Adult Neurogenesis

Tissue-nonspecific alkaline phosphatase is expressed both in the developing and adult mammalian brain. Expression is particularly strong in the developing nervous system and associated with neurogenic activity. It ceases during later development but high expression remains in the rodent adult subventricular zone of the lateral ventricles, a neurogenic niche generating new neurons for the olfactory bulb. Lower activity is maintained in specific brain regions. In spite of the wide expression of the enzyme very little is known concerning its regulation of expression and physiological function in nervous tissue. This may be one of the reasons why the expression of TNAP in the nervous system to date has received relatively little attention. The strong and in part transient expression of the enzyme in the developing brain implies, however, a significant role in the control of neural development. Interestingly, several factors that stimulate TNAP expression or activity have a strong impact on neural development. The chapter summarizes major findings regarding the cellular distribution of TNAP in the developing brain and the neurogenic niches of the adult brain and in vitro evidence for a functional role of TNAP in axon growth and progenitor cell proliferation and differentiation. Potential mechanisms of TNAP function are discussed.