Hpd, also known as 4-hydroxyphenylpyruvate dioxygenase, is a critical enzyme in tyrosine metabolism [1,2]. Tyrosine metabolism pathways are essential for various biological processes, and Hpd's function is crucial in maintaining normal physiological states. Deficiency in Hpd can lead to tyrosinemia, highlighting its importance in this metabolic context [1,2].

In Ttc36-/-mice, which lack the molecular chaperone TTC36, Hpd expression in the liver is reduced. This reduction is due to enhanced STK33-mediated HPD T382 phosphorylation, leading to increased PELI1-mediated Hpd polyubiquitylation and degradation. These Ttc36-/-mice exhibit tyrosinemia, damage to hippocampal neurons, and learning and memory deficits, revealing the role of Hpd in preventing tyrosinemia-associated neurological disorders [2].

In breast cancer, Hpd protein expression is increased compared to adjacent normal tissues. High Hpd expression is positively correlated with histological grade and clinical stage, and inversely correlated with 10-year overall survival rates, suggesting Hpd may be a prognostic predictor and potential therapeutic target [1].

In conclusion, Hpd is vital for tyrosine metabolism and its dysregulation can lead to tyrosinemia and associated neurological damage as shown in gene-knockout-like mouse models. In addition, its abnormal expression in breast cancer is related to prognosis, emphasizing its significance in both metabolic-related diseases and cancer research.