Crinophagy in Thyroid Follicular and Parafollicular Cells of Male Obese Zucker Rat

Abstract

Comparison between lean (Fa/?) and obese (fa/fa) young adult male Zucker rat thyroids reveals that obese rats display larger clusters of parafollicular cells than the lean ones with a lesser blood supply. Fa/? thyroid typically shows single or “twin” C cells in follicles; fa/fa parafollicular cells appear with three functional aspects. Crinophagy is found in the fa/fa C cells amassing numerous aberrant calcitonin-containing vesicles among which lysosomes build these autophagic bodies by capturing vesicle contents, other organelles and, fusing with each other, increase their size. Other C cells contain many secretory vesicles but show few or no crinophagic structures. Another parafollicular cell type is revealed with scant organelles and highly contrasted secretory vesicles, different from calcitonin. Hypercalcemia of fa/fa rats corresponds to increased C cells population with accrued calcitonin production but a low calcitonin plasma level – verified by others – is likely caused by crinophagy of the altered vesicles. In addition, the T thyrocytes of fa/fa rats exhibit crinophagy bodies; this can confirm their hypothyroidism. Possibly, the known leptin mutation along with other unknown paracrine secretions alter both T and C thyrocytes’ functions of the fa/fa rats, allowing high intracellular calcium and lower pH favoring autophagocytosis. Other longitudinal, interdisciplinary studies should further clarify the complex paracrine interactions existing between these endocrine structures because this animal model could be useful to understand human defects, such as the metabolic syndrome that involves obesity, cardiovascular, renal, hepatic, non-insulin dependent diabetes mellitus (NIDDM), hypothyroidism defects, as well as the etiology of thyroid medullary tumors.

• C thyrocyte
• calcitonin
• crinophagy
• male Zucker rat
• T thyrocyte
• thyroid gland

Acknowledgement

Ms K. Adamson, Northumbria University Graphics, is thanked for her technical assistance in the electronic treatment of the micrographs.

Declaration of interest

This report was accomplished in the KB Taylor Global Scholars’ Program, where DP completed his Medical Student training with this scholarly writing during Summer and Fall of 2014. Tissues from rats were donated by our late colleague Dr Judith A. Finkelstein, during Dr J. Gilloteaux tenure in the Department of Anatomy at Northeastern Ohio Universities College of Medicine, Rootstown, OH, USA with a research study sponsored by Biomedical Research Grant PHS-SO-7 R 058005-05 NEOUCOM, Rootstown, OH, USA. Old publications were accessed in the Library of the Institut Royal des Sciences Naturelles de Belgique, Brussels and of the Biomedical Library of the Katholieke Universiteit Leuven, Gasthuisberg. Leuven, Belgium with the kind assistance of their staff.

Notes

* This study is dedicated to the memory of the late Dr Judith C. Finkelstein, my former colleague at the Northeastern Ohio Universities College of Medicine (now named Northeast Ohio University), Rootstown, OH, USA.