NEDD4L induces mitochondrial dysfunction and neurodegeneration by promoting LIPT2 degradation in Huntington's disease

Impairment of mitochondrial protein stability is associated with neurodegeneration in Huntington's disease (HD). However, the E3 ligase responsible for maintaining mitochondrial protein homeostasis in HD remains poorly understood. In this study, we demonstrate that NEDD4L protein levels are elevated in human striatal organoids (hSOs) derived from induced pluripotent stem cells of patients as well as in a mouse model of HD. Overexpression of NEDD4L leads to degeneration and cell death of medium spiny neurons (MSNs), along with a reduction in motor activities. Conversely, deletion of NEDD4L restores abnormal MSN morphology, corrects deficits in calcium signaling, alleviates neurodegeneration in HD-hSOs, and improves motor dysfunction observed in YAC128 mice. Mechanistically, NEDD4L disrupts mitochondrial function by binding to lipoyl(octanoyl) transferase 2 (LIPT2) and promoting its degradation through ubiquitination and lysosomal pathways. This process impairs lipoic acid biosynthesis and the lipoylation of E2 subunits of alpha-ketoglutarate dehydrogenase (α-KGDH E2). Furthermore, either overexpressing LIPT2 or administering lipoic acid mitigates neurodegeneration and rectifies deficits in motor coordination activity. These findings unveil a molecular mechanism underlying the regulation of lipoic acid metabolism and underscore the potential therapeutic role of protein lipoylation in the treatment of HD.