Thyroid functions of mouse cathepsins B, K, and L
Bianca Friedrichs, … , Paul Saftig, Klaudia Brix
Bianca Friedrichs, … , Paul Saftig, Klaudia Brix
Published June 1, 2003
Citation Information: J Clin Invest. 2003;111(11):1733-1745. https://doi.org/10.1172/JCI15990.
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Thyroid functions of mouse cathepsins B, K, and L

Abstract

Thyroid function depends on processing of the prohormone thyroglobulin by sequential proteolytic events. From in vitro analysis it is known that cysteine proteinases mediate proteolytic processing of thyroglobulin. Here, we have analyzed mice with deficiencies in cathepsins B, K, L, B and K, or K and L in order to investigate which of the cysteine proteinases is most important for proteolytic processing of thyroglobulin in vivo. Immunolabeling demonstrated a rearrangement of the endocytic system and a redistribution of extracellularly located enzymes in thyroids of cathepsin-deficient mice. Cathepsin L was upregulated in thyroids of cathepsin K–/– or B–/–/K–/– mice, suggesting a compensation of cathepsin L for cathepsin K deficiency. Impaired proteolysis resulted in the persistence of thyroglobulin in the thyroids of mice with deficiencies in cathepsin B or L. The typical multilayered appearance of extracellularly stored thyroglobulin was retained in cathepsin K–/– mice only. These results suggest that cathepsins B and L are involved in the solubilization of thyroglobulin from its covalently cross-linked storage form. Cathepsin K–/–/L–/– mice had significantly reduced levels of free thyroxine, indicating that utilization of luminal thyroglobulin for thyroxine liberation is mediated by a combinatory action of cathepsins K and L.

Authors

Bianca Friedrichs, Carmen Tepel, Thomas Reinheckel, Jan Deussing, Kurt von Figura, Volker Herzog, Christoph Peters, Paul Saftig, Klaudia Brix

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Swelling of cathepsin D–containing lysosomes in thyroids of cathepsin B–...
Swelling of cathepsin D–containing lysosomes in thyroids of cathepsin B–/–, L–/–, or K–/–/L–/– mice. Confocal fluorescence micrographs of cryosections of thyroid glands from WT mice (+/+) or cathepsin-deficient mice of the indicated genotypes were immunolabeled with antibodies against cathepsin D (a and c–e). Diameters of cathepsin D–containing lysosomes were determined morphometrically and are given as means ± SE (b). In WT thyroid epithelial cells, cathepsin D–positive vesicles were distributed throughout the cells (a). An immunolabeling indicative of cathepsin D at the apical cell surface or over the follicle lumina was not observed in either genotype. The sizes of lysosomes of cathepsin K–/– or B–/–/K–/– thyrocytes were similar to those of WT controls (b), whereas those from cathepsin B–/–, L–/–, or K–/–/L–/– thyroid epithelial cells were significantly enlarged (c–e). Cathepsin D was absent from the inner portions of enlarged lysosomes of thyroid epithelial cells with a deficiency in cathepsin L (d, arrows). Similarly, cathepsin B (Cath B) immunostainings revealed ringlike lysosomes in L–/– thyrocytes (d, inset, arrows), indicating a tight association of cathepsins B and D with vesicular membranes in cathepsin L–deficient thyrocytes. N, nuclei. *P < 0.05, **P < 0.01. In b, n = 16, 12, 16, 19, 18, and 14, respectively, for sections of the different genotypes indicated. Bars: 20 μm.