Leptin/OB-R signaling is elevated in mice with Sjögren's syndrome and is implicated in disease pathogenesis

Lessons from Animal Models in Sjögren's Syndrome

Primary Sjögren's syndrome (pSS) is a connective tissue disease characterized by a wide spectrum of clinical features, extending from a benign glandular disease to an aggressive systemic disorder and/or lymphoma. The pathogenesis of Sjögren's syndrome (SS) is not completely understood, but it is assumed that pathogenesis of SS is multifactorial. The studies based on the animal models of SS provided significant insight in SS disease pathogenesis and management. The aim of this review is to summarize current studies on animal models with primary SS-like symptoms and discuss the impact of these studies on better understanding pathogenesis and management of Sjögren's syndrome. Databases PubMed, Web of Science, Scopus and Cochrane library were searched for summarizing studies on animal models in SS. Available data demonstrate that animal models are highly important for our understanding of SS disease.

Quercetin ameliorates salivary gland apoptosis and inflammation in primary Sjögren's syndrome through regulation of the leptin/OB-R signaling

Dry mouth is the main manifestation of Sjögren syndrome (SS). Quercetin has been reported to alleviate radiation-induced salivary gland damage, yet the effect of quercetin on SS-caused salivary gland damage remains unclear. This study aimed to investigate the effects of quercetin on SS-induced salivary gland damage and the mechanism underlying its therapeutic potential in SS. Here, NOD/Ltj mice were used to spontaneously mimic SS-induced salivary gland inflammation in vivo and salivary gland epithelial cells (SGECs) were stimulated by interferon-γ (IFN-γ) to mimic cell inflammation in vitro. Results showed that quercetin significantly reduced loss of saliva flow, salivary gland damage, cell apoptosis, and inflammatory response in NOD/Ltj mice. Quercetin treatment also significantly reduced the increased serum leptin (LP) levels in NOD/Ltj mice. Furthermore, quercetin blocked the increases in the expression of obesity receptor (OB-R) and its downstream Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling in the salivary glands. In vitro experiments confirmed that quercetin could protect SGECs from IFN-γ-induced cell apoptosis and inflammation through the LP/OB-R-activated JAK2/STAT3 signaling. Hence, quercetin might protect against SS-induced salivary gland damage by relieving cell apoptosis and inflammation by inhibiting the LP/OB-R signaling, providing a new perspective for treating SS-induced dry mouth.

Advances in Pathogenesis of Sjögren's Syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disease of unknown etiology that mainly involves exocrine glands. Patients present with dry mouth and eyes, fever, arthralgia, and other systemic symptoms. In severe cases, the quality of life of patients is affected. At present, there is no cure for SS, and the treatment options are extremely limited. In recent years, studies of patients and animal models have identified abnormalities of immune cell function and cytokines to be involved in SS. A systematic review of the literature may clarify the etiology and pathogenesis of SS, as well as provide a theoretical basis for the development of new drugs for the treatment of SS.

Serum levels of selected adipocytokines in benign and malignant parotid gland tumor patients

OBJECTIVES

The aim of this study was to evaluate serum levels of adiponectin, leptin, visfatin and IL-6 in patients with pleomorphic adenoma, Warthin's tumor and acinic cell carcinoma of the parotid gland.

MATERIALS AND METHODS

Venous blood samples were collected from 30 patients with pleomorphic adenoma, 21 patients with Warthin's tumor and 8 patients with acinic cell carcinoma. Serum adiponectin, leptin, visfatin, IL-6 and CRP concentrations were determined.

RESULTS

Our results revealed significantly lower adiponectin serum levels in patients with malignant tumors compared to benign tumor individuals. Moreover, in benign cases the level was significantly higher compared to controls. Furthermore, serum leptin concentrations of benign tumor patients were higher compared to controls. Those differences, however, were observed only in males. The serum visfatin level was elevated in all tumor subjects compared to healthy individuals, whereas the serum IL-6 concentration was similar.

CONCLUSIONS

We anticipate that adiponectin may play a potential protective role in salivary gland tumors. Also leptin and visfatin seem to play an important role in salivary gland tumor pathology, although in males and females leptin may act or be regulated in a different manner. The influence of visfatin on salivary gland tumors is probably independent of IL-6 production.

Leptin in autoimmune mechanisms of systemic rheumatic diseases

In the last two decades, white adipose tissue (WAT) has been recognized as a key actor of many physiological and pathological conditions. WAT is able to produce mediators, named "adipokines", which may affect systemic homeostasis. In particular, leptin is not only involved in appetite and energy metabolism, but also in immune system. Increasing evidence established that leptin can regulate both innate and adaptive immunity mainly with pro-inflammatory effects but also, to a lesser extent, with anti-inflammatory features. In autoimmune diseases, a failure or breakdown of the mechanisms of self-tolerance is observed. Leptin, which plays an important role in the control of immune balance, has been involved in autoimmunity generation and maintenance. In this review, it has been provided an up-to-date report about the role of leptin in systemic autoimmune diseases, with particular reference to connective tissue diseases, inflammatory arthritis, and vasculitis.

Leptin/OB-R pathway promotes IL-4 secretion from B lymphocytes and induces salivary gland epithelial cell apoptosis in Sjögren's syndrome

Sjögren's syndrome (SjS) is a chronic autoimmune epithelitis in which cell apoptosis promotes the formation of inflammatory lesions. We used immunohistochemistry and TUNEL to assay B cell infiltration and apoptosis in salivary gland tissue from 16-week-old NOD/LtJ mice with SjS. In co-cultures of primary salivary glandepithelial cells (SGECs) and spleen B cells, we assessed SGEC viability and apoptosis using CCK8 assays and flow cytometry. ELISAs were employed to assess cytokine levels in culture medium. Leptin protein, leptin receptor (OB-R), pro- and anti-apoptotic proteins, and Jak2/Stat3/ERK signaling molecules were analyzed using western blotting. B cell infiltration and salivary gland apoptosis were increased in salivary tissue from mice with SjS. Leptin treatment had no effect on cell viability or apoptosis among B cells and primary SGECs. B cell and SGEC co-culture systems showed that leptin increased apoptosis induced by B lymphocytes, reduced SGEC cell viability, and promoted IL-4 secretion from B cells. This suggests Leptin/OB-R signaling stimulates B cells-induced SGEC apoptosis via IL-4 secretion and OB-R-Jak2-Stat3 activation.