SHH and Huntington disease: We have reported before that Shh mediates brain-derived neurotrophic factor (BDNF)-induced neuroprotection against 3-nitropropionic acid (3-NP), which is an irreversible inhibitor of mitochondrial succinate dehydrogenase, also known as Complex II in the electron respiratory chain, that has been used to investigate the molecular mechanisms concerning cell death, mitochondrial dysfunction, and neurodegeneration in Huntington’s disease (HD) [47,49].