A novel mitochondrial tRNA(Ala) gene variant causes chronic progressive external ophthalmoplegia in a patient with Huntington disease

Hypoxia induces mitochondrial protein lactylation to limit oxidative phosphorylation

Oxidative phosphorylation (OXPHOS) consumes oxygen to produce ATP. However, the mechanism that balances OXPHOS activity and intracellular oxygen availability remains elusive. Here, we report that mitochondrial protein lactylation is induced by intracellular hypoxia to constrain OXPHOS. We show that mitochondrial alanyl-tRNA synthetase (AARS2) is a protein lysine lactyltransferase, whose proteasomal degradation is enhanced by proline 377 hydroxylation catalyzed by the oxygen-sensing hydroxylase PHD2. Hypoxia induces AARS2 accumulation to lactylate PDHA1 lysine 336 in the pyruvate dehydrogenase complex and carnitine palmitoyltransferase 2 (CPT2) lysine 457/8, inactivating both enzymes and inhibiting OXPHOS by limiting acetyl-CoA influx from pyruvate and fatty acid oxidation, respectively. PDHA1 and CPT2 lactylation can be reversed by SIRT3 to activate OXPHOS. In mouse muscle cells, lactylation is induced by lactate oxidation-induced intracellular hypoxia during exercise to constrain high-intensity endurance running exhaustion time, which can be increased or decreased by decreasing or increasing lactylation levels, respectively. Our results reveal that mitochondrial protein lactylation integrates intracellular hypoxia and lactate signals to regulate OXPHOS.

Atheromatosis of the Scalp: A Novel Feature of Chronic Progressive External Ophthalmoplegia Plus Due to a Single Mitochondrial DNA Deletion

Chronic progressive external ophthalmoplegia (CPEO) manifests phenotypically as ptosis with ophthalmoplegia or CPEO-plus, with the affection of muscles or organs other than the extra-ocular eye muscles. Herein, a case of CPEO-plus caused by a single mitochondrial DNA (mtDNA) deletion is represented, along with several previously unreported phenotypic features. The patient is a 76-year-old Caucasian female who had experienced slowly progressive bilateral ptosis since the age of 15, followed by gradual ophthalmoparesis without double vision. Since the age of 56, she had developed mild quadriparesis, depression, easy fatigability, hypersomnia, a facial tic, optic atrophy, cataract, glaucoma, hepatomegaly, hepatic steatosis, cholecystolithiasis, diverticulosis, hyperhidrosis, mild hyper-creatine-kinase-emia, hyperlipidemia, and hyperuricemia. Moreover, she had faced previously unreported manifestations of mitochondrial disorders, psoriasis, and multiple scalp atheromas. The phenotype and a single 5kb mtDNA deletion were employed to diagnose CPEO-plus. This case demonstrates that the phenotypic spectrum of CPEO-plus is broader than expected, that psoriasis and scalp atheromas are unique features of a mitochondrial disorder, and that CPEO progresses to CPEO-plus during the years.