Autophagy induction by tetrahydrobiopterin deficiency

Area of Science:

• Biochemistry
• Genetics
• Cell Biology

Background:

• Tetrahydrobiopterin (BH₄) deficiency is a genetic disorder linked to metabolic issues like phenylketonuria (PKU).
• The precise molecular mechanisms underlying BH₄ deficiency's impact on cellular signaling remain incompletely understood.

Purpose of the Study:

• To investigate the signaling pathway through which BH₄ deficiency impacts mTORC1 and autophagy.
• To explore the role of tyrosine in this pathway and its therapeutic potential.

Main Methods:

• Utilized BH₄-deficient Spr(-/-) mice and Pah(enu2) mouse models.
• Employed NIH3T3 cells under tyrosine restriction.
• Analyzed mTORC1 signaling and autophagic pathway activation.
• Assessed the effects of therapeutic tyrosine diet.

Main Results:

• BH₄ deficiency inactivated mTORC1 signaling and activated the autophagic pathway in mouse tissues.
• Tyrosine deficiency was identified as a key factor in mTORC1 inactivation and autophagy activation.
• Therapeutic tyrosine diet rescued dwarfism and mTORC1 inhibition but inactivated autophagy.
• mTORC1 inactivation and autophagy induction were observed in PKU patients with BH₄ deficiency.

Conclusions:

• BH₄ deficiency leads to tyrosine deficiency, causing mTORC1 inactivation and subsequent autophagy activation.
• Tyrosine availability is critical for regulating mTORC1 activity and autophagy.
• These findings provide novel insights into the pathophysiology of BH₄ deficiency and PKU.