Vps34/PIK3C3 deletion in thyroid impairs thyroid hormonogenesis and autophagic flux

BACKGROUND The production of thyroid hormones (T 3 , T 4 ) depends on thyroid organization in follicles, lined by a monolayer of thyrocytes with strict apico-basal polarity. Polarization supports vectorial transport of thyroglobulin for storage into, and recapture from, the colloid. It also allows selective addressing of channels, transporters, pumps and enzymes to their appropriate basolateral (NIS and Na + /K + -ATPase) or apical membrane domain (pendrin, anoctamin, DUOX2, DUOXA2 and TPO). How these actors of T 3 /T 4 synthesis reach their final destination remains poorly understood. Vps34/PIK3C3 is now recognized as a main component in the general control of vesicular trafficking and of cell homeostasis via autophagy. We recently reported that conditional Vps34 inactivation in kidney proximal tubular cells by Pax8-driven excision prevents normal addressing of apical membrane proteins and causes abortive macroautophagy. METHODS Vps34 was inactivated using a Pax8-driven Cre recombinase system. The impact of Vps34 inactivation in thyrocytes was analyzed by histological, immunolocalization and mRNA expression profiling. Thyroid hormone synthesis was assayed by 125 I injection and by serum plasma analysis. RESULTS Vps34 cKO mice were born at the expected Mendelian ratio and showed normal growth until postnatal day 14, then stopped growing and died at around 1 month of age. We therefore analyzed thyroid Vps34 cKO before postnatal day 14. We found that loss of Vps34 in thyrocytes causes: (i) disorganization of thyroid parenchyma with abnormal thyrocyte and follicular shape and reduced PAS + colloidal spaces; (ii) impaired 125 I organification at comparable uptake and frequent occurrence of follicles with luminal thyroglobulin but non-detectable T4-bearing thyroglobulin; (iii) severe non-compensated hypothyroidism with extremely low T 4 levels (<0.25 ± 1.5 μg/dL) and huge TSH plasma levels (19,300 ± 10,500 mU/L); (iv) intense signal in thyrocytes for the lysosomal membrane marker, LAMP-1, as well as thyroglobulin and the autophagy marker, p62, indicating defective proteolysis. CONCLUSIONS We conclude that Vps34 is crucial for thyroid hormonogenesis, at least by controlling delivery of apical actors responsible for biogenesis of thyroid hormones on Tg as well as defective proteolytic T 3 /T 4 excision in lysosomes.