HPDL DEFICIENCY IMPAIRS HUMAN CORTICAL NEUROGENESIS AND DRIVES NEURO-GLIA DEGENERATION THROUGH ALTERATIONS OF MITOCHONDRIAL FUNCTION

HPDL gene encodes a mitochondrial 4‑hydroxyphenylpyruvate dioxygenase‑like protein and LOF variants cause childhood‑onset hereditary spastic paraplegia (SPG83) with corticospinal tract degeneration and cortical abnormalities, yet HPDL dysfunction mechanism remains unclear. Here, we combined HPDL knockout neuroblastoma cells with patient‑derived iPSCs to define how HPDL loss alters mitochondrial bioenergetics and cortical neurogenesis. In neuroblastoma cells, HPDL deficiency compromises oxidative phosphorylation, impairing respirasome organization, and reducing complex I, III, and IV activity, thereby increasing ROS production. Consistently, bulk RNAseq highlights widespread gene dysregulation involved in oxidative metabolism and brain development.
In patient‑derived cortical progenitors, HPDL variants trigger premature neurogenesis, depleting proliferative pools and unbalancing deeper-layer cortical neuron production. Moreover, HPDL organoids show severely reduced growth, reminiscing microcephaly occurring in most severe SPG83 cases. Mitochondrial analyses in progenitors and immature neurons show defective respirasome assembly, reduced mitochondrial activity, increased ROS, and aberrant mitochondrial membrane potential sustained by reverse ATP-synthase activity. HPDL mutant cortical progenitor short‑term treatment with either 4‑hydroxybenzoate or mitochondria‑targeted antioxidant MitoTEMPO partially rescues premature neurogenesis in a mutation‑dependent manner, linking ROS imbalance to altered fate decisions.
Finally, patient-derived long‑term cortical differentiation reveals a synaptic marker reduction, combined with increased neuronal apoptosis, glial cell depletion, and early neurogenic regulator expression. These findings underline the crucial role of HPDL in proper cortical developmental programs and maintenance of synaptic and glial functions, redefining HPDL‑related disease as a combined neurodevelopmental and neurodegenerative disorder and highlighting the mitochondrial–ROS axis as a possible therapeutic target.