Annals of Medical Research DOI: 10.5455/annalsmedres.2019.01.039 2019;26(6):1118-22 Original Article Claudin-5 (tight junction) expression level changes in achilles tendon healing Alper Cirakli 1 , Havva Erdem 2 , Derya Cirakoglu 3 , Erdal Uzun 1 , Soner Cankaya 4 1 Ordu University, Faculty of Medicine, Department of Orthopedics and Traumatology, Ordu, Turkey 2 Ordu University, Faculty of Medicine, Department of Pathology, Ordu, Turkey 3 Ordu University Training and Research Hospital, Department of Physical Medicine and Rehabilitation, Ordu, Turkey 4 Ondokuz Mayis University Faculty of Medicine, Department of Biostatistics, Samsun, Turkey Copyright © 2019 by authors and Annals of Medical Research Publishing Inc. Abstract Aim: This study aimed to reveal the relationship between changes in Claudin-5 expression and the duration of healing in Achilles tendon injury. Material and Methods: 18 Achilles tendons of Wistar-Albino rats were used in the study. Rats were divided into 3 groups as 6 rats in each group, group 1; sham group, group 2; tendon repair group (sacrifced after 3 weeks), group 3; tendon repair group (sacrifced after 6 weeks). Immunohistochemically, the tendons were stained with Claudin-5 and the degree of staining with light microscope was rated between 0 and 3. The obtained scores were compared with Kruskal Wallis test and Posthoc analysis. Results: The scores were 0.5 ± 1 (0-1) in group 1.1 ± 1 (1-2) in group 2 and 1.5 ± 1 (1-2) in group 3. A statistically signifcant difference was found between the groups (p = 0.026). In the posthoc analyzes, there was a signifcant difference between group 1 and 3, but there was no signifcant difference between groups 1 and 2 and between groups 2 and 3. Conclusion: The expression of claudins is regulated by many factors, including hormones, various cytokines, and epithelial- mesenchymal transition-related transcription factors. In this study, the increase in the expression of Claudin-5 was noticed in proportion to the progress of primary wound healing. This relationship may be a part of the repair mechanism. The role of claudin levels in intercellular passage is crucial for function as it is important for cell signaling. Achilles tendon healing can be attributed to a laboratory parameter such as claudin. This can help to understand the recovery rate and can help early return to work or sport. We believe that as a laboratory parameter Claudin-5 may be useful in the evaluation of tendon healing. Keywords: Claudin-5; healing; tendon; achilles; rat. Received: 13.02.2019 Accepted: 06.05.2019 Available online: 13.05.2019 Corresponding Author: Erdal Uzun, Ordu University, Faculty of Medicine, Department of Orthopedics and Traumatology, Ordu, Turkey E-mail: nuzuladre@gmail.com 1118 INTRODUCTION The junctions which extend adjacent to the cell membrane side surface’s apical end are called Tight junctions. Barrier function and containment function are their two main functions: Regulation of ions’s passage, water and macromolecules through paracellular spaces are the barrier function; and it also applies to cancer cells (1). Cell polarity are provided by surrounding function (1,2). Exchange and signaling are formed by Tight binding proteins which regulate proliferation, cell growth, differentiation and dedifferentiation (2). There are a lot of different proteins in the tight junctions of the epithelium, endothelium and myelinated cells. Ocular and claudin are two main components of tight junction flaments. Claudin is a family of proteins with more than 20 members (1-4). Claudins are barrier forming proteins which make paracellular permeability arrangements. They can form especially small pores or provide water permeability (1-4). The claudins are thought to be the main determinants of the epithelial cells’ permeability properties. Too many claudins identifed in mammals and they are divided into eight subgroups; expression is made by a tissue-specifc manner and are scattered throughout epithelium’s all cell-cell contact regions. The function and tissue specifcity of the claudins are well-known. At tight junctions multiple claudin isoforms are expressed concurrently (3-5). Loss of cell polarity is a function of epithelial-mesenchymal transition, a function that is clearly regulated by tightly linked proteins (6).