Epigallocatechin gallate stimulates the neuroreactive salivary secretomotor system in autoimmune sialadenitis of MRL-Faslpr mice via activation of cAMP-dependent protein kinase A and inactivation of nuclear factor κB

Abstract

The water channel aquaporin 5 (AQP5) plays a crucial role in regulating salivary flow rates. Xerostomia is often observed in patients with Sjögren's syndrome, and this is attributed to reduced AQP5 expression in the salivary glands. Recently, anti-type 3 muscarinic cholinergic receptors (M₃R) autoantibodies and nuclear factor κB (NF-κB) have been found to be negative regulators of AQP5 expression in the salivary gland. Anti-M₃R autoantibodies desensitize M₃R to salivary secretagogues in Sjögren's syndrome, while activated NF-κB translocates to nuclei and binds to the AQP5 gene promoter, resulting in the suppression of AQP5 expression. We previously documented that epigallocatechin gallate (EGCG), which is a robust antioxidant contained in green tea, ameliorates oxidative stress-induced tissue damage to the salivary glands of MRL/MpJ-lpr/lpr (MRL-Fas^lpr) mice, which are widely used as a model of Sjögren's syndrome. Reactive oxygen species (ROS) can activate NF-κB and inactivate protein kinase A (PKA), which is a key driver of AQP5 expression. In this study, we examined the effects of administering EGCG to MRL-Fas^lpr mice with autoimmune sialadenitis on the levels of AQP5, activated NF-κB p65 subunit, activated PKA, activated c-Jun N-terminal kinase (JNK) (an activator of NF-κB), inhibitor κB (IκB) and histone deacetylase 1 (HDAC1) (an inhibitor of NF-κB). In EGCG-treated mice, intense aster-like immunostaining for AQP5 was observed on the apical plasma membranes (APMs) of submandibular gland acinar cells. Likewise, PKA, IκB and HDAC1 were highly expressed in salivary gland tissues, whereas the expression of JNK and NF-κB p65 was negligible. Rank correlation and partial correlation analyses revealed that treatment with EGCG upregulated AQP5 expression on the APM of acinar cells through activation of PKA and inactivation of NF-κB, while IκB and HDAC1 played a pivotal role in the induction of AQP5 expression by PKA. Our study indicates that EGCG may have therapeutic potential for Sjögren's syndrome patients.     

The role of aquaporin-1 in idiopathic and drug-induced intracranial hypertension

Idiopathic intracranial hypertension is a common disorder affecting mainly healthy, young, overweight women. The pathogenesis of this condition is unknown, but it has been shown to follow treatment with several compounds including corticosteroids and vitamin A derivatives. This paper will offer a novel hypothesis and insight on the pathogenesis of drug induced intracranial hypertension following a review and analysis of the literature. Both corticosteroids and vitamin A derivatives have been shown to upregulate the expression of aquaporin 1, a water channel protein. Aquaporin 1 is widely distributed in the human brain and is associated with water secretion into the subarachnoid space. Aquaporin 1 was also shown to participate in the regulation of weight. Agents used for treating idiopathic intracranial hypertension reduce aquaporin 1 expression. Based on these observations, we propose that aquaporin 1 has a pathogenetic role in drug induced idiopathic intracranial hypertension. Over expression of this gene causes increased intracranial pressure, and downregulation reduces pressure and alleviates the symptomatology and complications of idiopathic intracranial hypertension.     

Postmortem immunohistochemical alterations following cerebral lesions: A possible pathohistological importance of the β‐dystroglycan immunoreactivity

The frequency of cerebrovascular injuries raises the importance of their immunohistological investigation in postmortem materials. Most injuries involve the impairment of the blood–brain barrier. The barrier is maintained by the glio‐vascular connections which break up following injuries. Some immunohistochemical alterations may refer to the impairment of the gliovascular connections. Laminin and the components of the dystroglycan complex show characteristic immunohistochemical alterations following various experimental injuries (stab wound, cryogenic lesion, arterial occlusions): immunoreactivity of β‐dystroglycan, α‐dystrobrevin and aquaporin 4 disappeared while that of utrophin and laminin appeared along the vessels, whereas α‐syntrophin visualized the reactive astrocytes but not the resting ones. The aims of the present study were to investigate whether these post‐lesion alterations: (i) are reproducible with immersive fixation, which is used in postmortem histology; (ii) are resistant to a postmortem delay before fixation; and (iii) are to be attributed to a direct effect of the lesion, or are mediated by processes occurring only in the living brain. Three models were investigated: (i) following lesions, some brains were fixed by transcardial perfusion, others by immersion; (ii) following lesions, the animals were decapitated and stored at room temperature for 8 or 16 h before fixation; and (iii) the lesions were performed after decapitation. Cryogenic lesions were performed by applying a dry ice cooled copper rod to the brain surface of ketamine‐xylazine anesthetized rats. The immunohistochemical reactions were performed on free‐floating sections cut with vibratome. Both immunoperoxidase and immunofluorescence methods were used. The fixation method – perfusive or immersive – did not change the post‐lesion phenomena investigated. The postmortem delay did not influence the β‐dystroglycan immunoreactivity, that is its lack delineated the area of the lesion. However, in the case of the other substances, various lengths of postmortem delay rendered the immunohistochemistry uninterpretable. The results suggest β‐dystroglycan immunostaining could be applied in the neuropathology to detect cerebrovascular impairments.     

大鼠出血性脑水肿水通道蛋白4表达的研究

目的 :探讨大鼠脑出血后血肿周围水通道蛋白 4(AQP4)的表达变化。方法 :采用定量胶原酶注入大鼠尾状核建立脑出血模型 ,用干湿重法和免疫组织化学法分别检测脑出血后不同时间段脑含水量和 AQP4蛋白的表达。结果 :脑出血后 6h,脑含水量和血肿周围 AQP4蛋白表达增加 ;出血后 72 h达到高峰 ,出血 1周后仍高于正常 ;AQP4蛋白的表达和脑含水量呈显著正相关 (r=0 .985 7,P<0 .0 1)。结论 :AQP4与出血性脑水肿的形成密切相关     

Permeability of the plasma membrane to water and cryoprotectants in mammalian oocytes and embryos: Its relevance to vitrification

The permeability of the plasma membrane to water and cryoprotectants is one of the important factors for determining the suitable condition for the vitrification of mammalian oocytes and embryos. Water and cryoprotectants move slowly through oocytes and early embryos, principally by simple diffusion, in the mouse, bovine, pig, and human. In contrast, water, glycerol, and ethylene glycerol move rapidly through morulae and blastocysts, principally by facilitated diffusion via aquaporin 3, in the mouse and bovine; whereas, in the pig, the permeability to water and these cryoprotectants increases not at the morula stage but at the blastocyst stage and further increases at the expanded blastocyst stage. Dimethyl sulfoxide also moves rapidly via channels other than aquaporin 3 in the mouse. In contrast, propylene glycol moves through morulae and blastocysts principally by simple diffusion in the mouse, bovine, and pig, as through oocytes. Therefore, the permeability of mammalian oocytes and embryos at early stages to water and cryoprotectants is low, but that of embryos at later stages to water and some cryoprotectants is markedly high by channel processes, although species specificity exists in some cases.     

水通道蛋白4在大鼠脑垂体中的表达

目的：研究水通道蛋白4(AQP4)及其mRNA在脑垂体中的表达,探讨其在脑垂体激素分泌过程中的作用。方法：应用免疫组织化学和原位杂交技术,观察成年Wistar大鼠脑垂体中AQP4及其mRNA的正常分布。结果：AQP4及其mRNA在成年大鼠神经垂体的垂体细胞上表达呈阳性,分布在毛细血管窦周围的垂体细胞表达尤为强烈。腺垂体的所有细胞均有AQP4的表达,胞质中AQP4 mRNA表达呈阳性。中间叶所有细胞AQP4及其mRNA的表达呈弱阳性,其中滤泡星形细胞表达较内分泌细胞强烈。结论：AQP4广泛分布于脑垂体的各种组织细胞表面,可能在垂体激素的正常分泌过程中起重要的调节作用。     

水通道蛋白5在大鼠大脑组织中的分布及表达

目的:观察水通道蛋白5(AQP5)在大鼠脑组织中的分布和表达,为研究脑组织中水分子的运输和平衡机制提供形态学基础。方法:运用免疫组织化学和免疫荧光技术,观察正常成年Wistar大鼠脑组织中AQP5的分布;运用免疫印迹观察AQP5的表达,并与AQP4在脑组织的分布和表达进行比较。结果:AQP5分布于大脑皮质的软脑膜、脉络丛、血管周围、海马锥体细胞层、齿状回颗粒细胞层、视上核、视交叉上核内和大脑纵裂两侧皮质深部,与AQP4分布范围相似;除此以外,AQP5还独自分布于大脑皮质下神经细胞。免疫印迹显示AQP5表达明显弱于AQP4。结论:AQP5在大鼠脑组织中分布广泛,可能协同AQP4在脑组织水运输平衡,脑脊液产生与回流及渗透压的调节过程中,发挥重要作用。