Elsevier

Human Pathology

Volume 65, July 2017, Pages 231-238
Human Pathology

Original contribution
Down-regulation of polycystin in lymphatic malformations: possible role in the proliferation of lymphatic endothelial cells,☆☆

https://doi.org/10.1016/j.humpath.2017.05.016Get rights and content

Highlights

  • PC-1 and PC-2 were down-regulated in LMs compared with normal human skin tissues.

  • Expression of PC-1 and PC-2 was negatively correlated with phosphorylation of ERK in LMs.

  • PC-1/2 and ERK pathway may contribute to increased proliferation activity of LECs in LMs.

Summary

Lymphatic malformations (LMs) are composed of aberrant lymphatic vessels and regarded as benign growths of the lymphatic system. Recent studies have demonstrated that the mutant embryos of PKD1 and PKD2, encoding polycystin-1 (PC-1) and polycystin-2 (PC-2), respectively, result in aberrant lymphatic vessels similar to those observed in LMs. In this study, for the first time, we investigated PC-1 and PC-2 expression and assessed their roles in the development of LMs. Our results demonstrated that PC-1 and PC-2 gene and protein expressions were obviously decreased in LMs compared with normal skin tissues. In addition, the expression of phosphorylated ERK but not total ERK was up-regulated in LMs and negatively correlated with the expression of PC-1 and PC-2. Moreover, up-regulation of Ki67 was detected in LMs and positively correlated with ERK phosphorylation levels. Furthermore, cluster analysis better reflected close correlation between these signals. All of the above results provided strong evidence suggesting that the hyperactivation of the ERK pathway may be caused by down-regulation of PC-1 and PC-2 in LMs, contributing to increased proliferation of lymphatic endothelial cells in LMs. Our present study sheds light on novel potential mechanisms involved in LMs and may help to explore novel treatments for LMs.

Introduction

Lymphatic malformations (LMs) are slow-flow vascular anomalies characterized by ectatic lymphatic vessels filled with proteinaceous fluid [1]. With a reported incidence of 1.2 to 2.8 per 1000 births [2], LMs are typically congenital and present at birth [3]. Most of these lesions appeared in the head and neck areas and lead to the deformity [3]. Under certain pathological conditions (eg, infection, trauma), LMs may rapidly enlarge, resulting in dysphasia and even life-threatening complications [2]. Although great progress has been made, curative effects of diffuse LMs remain far from satisfactory. Moreover, basic studies on the mechanisms of LMs are rarely performed.

Polycystins are transmembrane proteins composed of multiple members, among which polycystin-1 (PC-1) and polycystin-2 (PC-2) are of particular concern [4], [5]. PC-1 and PC-2, which are encoded by PKD1 and PKD2, respectively, are expressed in various cells (eg, epithelial and endothelial cells) and regulate cell function and proliferation [5], [6]. Numerous studies have demonstrated that mutations in these 2 genes could result in fluid-filled cysts of the kidney known as autosomal dominant polycystic kidney disease and severe cardiovascular complications affecting humans [5], [7]. More recent studies have demonstrated that PKD1 and PKD2 also play important roles in lymphatic development [5], [8]. Most importantly, distended lymphatic capillary and lymphatic vessel defects are detected in PKD-null embryos in mice [5], [8]. Nevertheless, the expression change and potential roles of PC-1 and PC-2 in LMs remain largely unknown.

Previous studies have demonstrated that abnormal proliferation of lymphatic endothelial cells (LECs) and lymphangiogenesis are involved in the rapid progress of LMs [1], [9]. In addition, PC-1 and PC-2 regulate the activation of ERK signaling, which affects LEC proliferation and lymphatic vessel growth [6], [10], [11]. Given that Ki67 is a representative biomarker for the evaluation of cell proliferation, we evaluated the protein and gene expression levels of PC-1, PC-2, ERK, and proliferation-related molecule Ki67 in LMs and normal human skin tissues by immunoreactivity and real-time polymerase chain reaction (PCR). In addition, the correlations among these molecules were analyzed to determine their roles in the progression of LMs.

Section snippets

Clinical samples and immunohistochemistry

Twenty-one samples of primary LMs and 10 samples of healthy donor skin were collected at the Hospital of Stomatology, Wuhan University. Informed consent was obtained from all individual participants included in the study. According to guidelines of the National Institutes of Health, the specimens were fixed in buffered 4% paraformaldehyde, embedded in paraffin, and cut into 4-μm sections for immunostaining. The study was approved by the review board of the ethics committee of the Hospital of

PC-1 and PC-2 expression was significantly down-regulated in the LECs of LMs

Initially, LYVE-1 and Prox-1 were used to confirm the location of lymphatic vessels and LECs in 10 normal skin tissue samples and 21 clinical LM samples. The information from patients with LMs is presented in Supplementary Table 2. Immunohistochemical images of LYVE-1–positive and Prox-1–positive staining in the detected specimens are presented in Supplementary Fig. 1. Subsequently, PC-1 and PC-2 expression levels were investigated. As presented in Fig. 1A-D, both PC-1 and PC-2 were strongly

Discussion

LMs are composed of aberrant lymphatic vessels and regarded as benign growths of the lymphatic system [1]. Previous studies have reported that clinical features of LMs may result from dysregulated lymphatic overgrowth and remodeling [1]. Undoubtedly, LEC proliferation plays critical roles in the above processes. In the present study, the up-regulation of Ki67, a representative biomarker of cell proliferation, was noted in the LECs of LMs compared with normal skin tissues, indicating increased

Supplementary data

The following are the Supplementary data to this article.

Supplementary materials

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    • Recent Progress in Lymphangioma

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    Competing interests: The authors have no conflict of interest related to this article.

    ☆☆

    Funding/Support: This work was supported by the Fundamental Research Funds for the Central Universities (413000003) to Dr J. G. Ren and the grants from the National Natural Science Foundation of China (81500379 and 81371159) to Dr Y. F. Sun and to Professor Y. F. Zhao, respectively.

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