Role of Phosphodiesterases in Huntington's Disease.

Huntington's disease (HD) is an autosomal-dominant rare inherited neurodegenerative disease characterized by a wide variety of symptoms encompassing movement, cognition and behaviour. The cause of the disease is a genetic mutation in the huntingtin protein. The mutation leads to an unstable CAG expansion, translated into a polyglutamine domain within the disease protein. Indeed, huntingtin has a CAG/polyglutamine expansion in the range of 6-39 units in normal individuals, whereas it reaches 39-180 units in HD patients. Mutant huntingtin interacts with and impairs the function of a number of transcription factors. Indeed, the expression and function of cAMP response element-binding protein (CREB) and the brain-derived neurotrophic factor (BDNF) are severely affected in HD. Drugs targeting CREB loss of function and BDNF decrease have been considered as powerful tools to treat HD. Recently, cyclic nucleotide phosphodiesterase (PDE) inhibitors have been shown to reduce striatal and cortical degeneration in transgenic mouse model of HD. The neuroprotective effect is due to the competency of PDE4, 5 and 10 inhibitors to positively modulate CREB and BDNF protein levels, both in striatum and cortex in HD models. In this chapter, we will summarize the data supporting the use of PDE inhibitors as a therapeutic approach to fight HD, deepening the possible mechanisms of action underlying these effects.