Elsevier

Archives of Oral Biology

Volume 53, Issue 9, September 2008, Pages 835-841
Archives of Oral Biology

Expression of podoplanin in the mouse salivary glands

https://doi.org/10.1016/j.archoralbio.2008.02.006Get rights and content

Abstract

Objective

Podoplanin is one of the most highly expressed lymphatic-specific genes. Here, we report the distribution of cells expressing podoplanin in mouse salivary glands.

Design

We immunohistochemically investigated the distribution of cells expressing podoplanin in mouse major salivary glands by laser-scanning microscopy. The expression of endothelial cell marker PECAM-1 was tested to discriminate lymphatic endothelium from salivary gland cells, and myoepithelial cells were identified by an antibody for P-cadherin.

Results

The podoplanin expression was rarely found in acini of the parotid gland but clearly found at the basal portion of acini in the submandibular and sublingual glands. The number of portion reacted with anti-podoplanin is greater in the sublingual gland than in the submandibular gland. The expression was also found at the basal portion of ducts in all major salivary glands. The P-cadherin expression was rarely found in acini of the parotid gland but found in acini of the sublingual gland and on ducts in parotid and sublingual glands, corresponding to the area of podoplanin expression.

Conclusions

It was suggested that the acinar and myoepithelial cells in the salivary glands have the ability to express podoplanin, and that the expression may be concerned with the mucous saliva excretion.

Introduction

Podoplanin, a 43-kDa transmembrane glycoprotein, is one of the most highly expressed lymphatic-specific genes and is regulated by homeobox gene Prox1.1, 2, 3, 4 The podoplanin expression in lymphatic endothelium was first reported as E11 antigen and was further identified as podoplanin because of the expression in kidney glomerular epithelial cells (podocytes).5, 6Podoplanin is homologous to T1α encodes an antigen expressed at alveolar type I cells in rat lung.7, 8Podoplanin−/− mice die at birth because of respiratory defect and congenital lymphedema due to the failure in lymphatic pattern formation. In the level of cultured cell it has been indicated that the lymphatic tube formation is based on the cell adhesion with podoplanin at the cell–cell contact.9

On the other hand it is well established that the mouse parotid, submandibular, and sublingual glands are composed of serous, seromucous, and mucous-dominant mixed acinar cells, respectively.10, 11, 12 The determinant for the viscosity of saliva is the glycoprotein mucins which protect mucosal cell membranes against proteases. The submandibular gland secretes 30% of the salivary mucins while sublingual and a large number of minor glands of palate, cheeks and lips secrete 70%. Concentration of mucin secreted by the sublingual gland is higher than that secreted by the submandibular gland, while the secretion of parotid gland is almost devoid of mucins.13, 14, 15 It has been reported that podoplanin is resistant to proteases because of the negatively charged mucin-type protein.6, 14 It is thought that the expression of transmembrane protein podoplanin may contribute to protecting salivary gland cells from protease by covering the cell surface with mucin. The expression of podoplanin in the several epithelial cells, such as epidermis and alveolar epithelia, has been noticed but little is known on the expression in salivary glands.16, 17

Platelet-endothelial cell adhesion molecule-1 (PECAM-1) is a well-established endothelial cell marker generally expressed on leukocytes and endothelial cells. The PECAM-1 is a 130-kDa type I transmembrane glycoprotein belonging to the immunoglobulin superfamily and acts as an adhesion molecule.18, 19, 20, 21 In this study the expression of PECAM-1 was immunohistochemically tested to discriminate lymphatic vessels from salivary gland cells since the lymphatic endothelium expresses both podoplanin and PECAM-1. The study here was designed to investigate the distribution of cells expressing podoplanin in mouse major salivary glands.

Section snippets

Materials and methods

Eight-week-old wild-type male mice (C57BL6/J, n = 5) purchased from the Jackson Laboratory (Bar Harbor, ME, USA) were used. The collection of the tissue was conducted after euthanasia by intraperitoneal injection with sodium pentobarbital (10 ml/kg, Nembutal, Abbott Laboratories, North Chicago, IL). Mice were perfused through the heart with 4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.4). The protocol for animal use was reviewed and approved by the animal experiment committee of Fukuoka

Immunohistochemistry of the mouse kidney and tongue

The mouse kidney and tongue tissue was used to test the specificity of anti-podoplanin (Fig. 1). The immunostaining with anti-PECAM-1 was simultaneously performed to identify lymphatic vessels because anti-podoplanin also reacts to the lymphatic endothelium. Reaction products with anti-PECAM-1 were only detected on blood vessels including glomerular arteriole and on lymphatic vessels. Reaction products with anti-podoplanin were only detected on podocytes and lymphatic vessels.

Immunohistochemistry of the mouse major salivary glands

In the mouse

Discussion

Podoplanin is a transmembrane protein expressed in podocytes, alveolar epithelial type I cells, mesothelial cells and lymphatic endothelial cells.1, 6 In this study the strong reaction with anti-podoplanin was detected on podocytes and lymphatic vessels but not on blood vessels, uriniferous tubules, and muscle and connective tissue, suggesting that the specificity of the antibody for podoplanin is reliable (Fig. 1). The expression of podoplanin was rarely found in serous acini of the parotid

References (27)

  • T.V. Petrova et al.

    Lymphatic endothelial reprogramming of vascular endothelial cells by the Prox-1 homeobox transcription factor

    EMBO J

    (2002)
  • S. Breiteneder-Geleff et al.

    Podoplanin, novel43-kd membrane protein of glomerular epithelial cells, is down-regulated in puromycin nephrosis

    Am J Pathol

    (1997)
  • J. Bolscher et al.

    Distinct populations of high-M(r) mucins secreted by different human salivary glands discriminated by density-gradient electrophoresis

    Biochem J

    (1995)
  • Cited by (0)

    View full text