Sequential activation of individual caspases, and of alterations in Bcl-2 proapoptotic signals in a mouse model of Huntington's disease.

Caspases play an important role in neurodegeneration in Huntington's disease (HD). Members of the Bcl-2 family are critical modulators of terminal cell death pathways. However, alterations of Bcl-2 family members and their functional role in an in vivo model of HD have not been documented. With the goal of gaining mechanistic insight, we used a transgenic mouse model of HD (R6/2) to investigate the chronology of caspase activation and functional alterations in members of the Bcl-2 family. In R6/2 mice caspase activation precedes proapoptotic changes in Bcl-2 family members. Of the caspases that we screened, caspase-1-like activation was the first to be detected in the disease process (7 weeks). Proapoptotic changes in members of the Bcl-2 family were first detected at 9 weeks. To demonstrate a potential functional/therapeutic role of Bcl-2 in HD, we crossed R6/2 mice with mice overexpressing Bcl-2 in neurons. Transgenic expression of Bcl-2 in R6/2 mice resulted in slight prolonged survival. Understanding the chronology of apoptotic events provides important information for appropriate therapeutic targeting in this devastating and untreatable disease.