Impaired striatal function in Huntington's disease is due to aberrant p75NTR signaling

Huntington's disease (HD) is a rare genetic neurodegenerative disorder for which there is currently no cure. Early hyperkinetic motor symptoms are consistent with reduced activity of indirect pathway striatal projection neurons (iSPNs) responsible for suppression of unwanted actions. Our recent work suggests that one of the factors contributing to this deficit is impaired brain-derived neurotrophic factor (BDNF) signaling that regulates the strength of iSPN excitatory synapses. Specifically, we found that BDNF-dependent corticostriatal synaptic long-term potentiation (LTP) was lost in iSPNs from 2 genetic models of HD, just as they began to robustly manifest motor symptoms. This deficit was not attributable to problems in BDNF production, delivery or receptor binding. Rather, the plasticity deficit stemmed from enhanced signaling through p75 neurotrophin receptors (p75(NTRs)) and the phosphatase and tensin homolog (PTEN), leading to antagonism of intracellular TrkBR cascades and LTP. This study suggests HD therapeutics should target p75(NTR) signaling, not TrkBR.