Enhanced expression of aquaporin-9 in rat brain edema induced by bacterial lipopolysaccharides

Human Aquaporins: Functional Diversity and Potential Roles in Infectious and Non-infectious Diseases

Aquaporins (AQPs) are integral membrane proteins and found in all living organisms from bacteria to human. AQPs mainly involved in the transmembrane diffusion of water as well as various small solutes in a bidirectional manner are widely distributed in various human tissues. Human contains 13 AQPs (AQP0-AQP12) which are divided into three sub-classes namely orthodox aquaporin (AQP0, 1, 2, 4, 5, 6, and 8), aquaglyceroporin (AQP3, 7, 9, and 10) and super or unorthodox aquaporin (AQP11 and 12) based on their pore selectivity. Human AQPs are functionally diverse, which are involved in wide variety of non-infectious diseases including cancer, renal dysfunction, neurological disorder, epilepsy, skin disease, metabolic syndrome, and even cardiac diseases. However, the association of AQPs with infectious diseases has not been fully evaluated. Several studies have unveiled that AQPs can be regulated by microbial and parasitic infections that suggest their involvement in microbial pathogenesis, inflammation-associated responses and AQP-mediated cell water homeostasis. This review mainly aims to shed light on the involvement of AQPs in infectious and non-infectious diseases and potential AQPs-target modulators. Furthermore, AQP structures, tissue-specific distributions and their physiological relevance, functional diversity and regulations have been discussed. Altogether, this review would be useful for further investigation of AQPs as a potential therapeutic target for treatment of infectious as well as non-infectious diseases.

Involvement of JNK/NFκB Signaling Pathways in the Lipopolysaccharide-Induced Modulation of Aquaglyceroporin Expression in 3T3-L1 Cells Differentiated into Adipocytes

Aquaglyceroporins, belonging to the family of aquaporins (AQPs), are integral plasma membrane proteins permeable to water and glycerol that have emerged as key players in obesity. The aim of this study was to investigate the expression profile of AQPs in undifferentiated and differentiated 3T3-L1 cells and to investigate the changes in expression of aquaglyceroporins in 3T3-L1 cells differentiated into adipocytes and subjected to lipopolysaccharide (LPS) mimicking inflammation occurring during obesity. Furthermore, the study aimed at identifying the signaling cascade involved in the regulation of aquaglyceroporins expression upon LPS stimulation. 3T3-L1 cells were grown as undifferentiated cells (UDC; preadipocytes) or cells differentiated into adipocytes (DC, adipocytes). DC were incubated in the presence or absence of LPS with or without inhibitors of various protein kinases. AQPs mRNA expression levels were measured by real-time quantitative polymerase chain reaction (RT-qPCR). AQP1, AQP2, AQP3, AQP9 and AQP11 mRNA were expressed in both UDC and DC, whereas AQP4, AQP7 and AQP8 mRNA were expressed only in DC. In DC, LPS up-regulated AQP3 mRNA levels (p < 0.05) compared to control; these effects were inhibited by CLI095, SP600125 and BAY11-7082 (p < 0.05). LPS decreased both AQP7 and AQP11 mRNA levels (p < 0.01) in DC as compared to control; this decrease was inhibited by CLI095 and BAY11-7082 (p < 0.05) and additionally by SP00125 for AQP7 (p < 0.05). SB203580 had no effect on LPS-induced AQP3, AQP7 and AQP11 mRNA levels modulations. In conclusion, our results clearly show that many AQPs are expressed in murine 3T3-L1 adipocytes. Moreover, in DCs, LPS led to decreased AQP7 and AQP11 mRNA levels but to increased AQP3 mRNA levels, resulting from the Toll-like receptor 4 (TLR4)-induced activation of JNK and/or NFκB pathway.

Pseudomonas aeruginosa lasI/rhlI quorum sensing genes promote phagocytosis and aquaporin 9 redistribution to the leading and trailing regions in macrophages

Pseudomonas aeruginosa controls production of its multiple virulence factors and biofilm development via the quorum sensing (QS) system. QS signals also interact with and affect the behavior of eukaryotic cells. Host water homeostasis and aquaporins (AQP) are essential during pathological conditions since they interfere with the cell cytoskeleton and signaling, and hereby affect cell morphology and functions. We investigated the contribution of P. aeruginosa QS genes lasI/rhlI to phagocytosis, cell morphology, AQP9 expression, and distribution in human macrophages, using immunoblotting, confocal, and nanoscale imaging. Wild type P. aeruginosa with a functional QS system was a more attractive prey for macrophages than the lasI/rhlI mutant lacking the production of QS molecules, 3O-C₁₂-HSL, and C₄-HSL, and associated virulence factors. The P. aeruginosa infections resulted in elevated AQP9 expression and relocalization to the leading and trailing regions in macrophages, increased cell area and length; bacteria with a functional QS system lasI/rhlI achieved stronger responses. We present evidence for a new role of water fluxes via AQP9 during bacteria–macrophage interaction and for the QS system as an important stimulus in this process. These novel events in the interplay between P. aeruginosa and macrophages may influence on the outcome of infection, inflammation, and development of disease.

The anterior commissure is a pathway for contralateral spread of herpes simplex virus type 1 after olfactory tract infection

Herpes simplex encephalitis (HSE), targeting the limbic system, is the most common cause of viral encephalitis in the Western world. Two pathways for viral entry to the central nervous system (CNS) in HSE have been suggested: either via the trigeminal nerve or via the olfactory tract. This question remains unsettled, and studies of viral spread between the two brain hemispheres are scarce. Here, we investigated the olfactory infection as a model of infection and tropism of herpes simplex virus 1 (HSV-1), the causative agent of HSE, in the CNS of rats. Rats were instilled with HSV-1 in the right nostril and sacrificed 1-6 days post-infection, and tissues were analysed for viral spread using immunohistochemistry and quantitative PCR (qPCR). After nasal instillation, HSV-1 infected mitral cells of the olfactory bulb (OB) on the right side only, followed by limbic encephalitis. As a novel finding, the anterior commissure (AC) conveyed a rapid transmission of virus between the right and the left OB, acting as a shortcut also between the olfactory cortices. The neuronal cell population that conveyed the viral infection via the AC was positive for the water channel protein aquaporin 9 (AQP9) by immunohistochemistry. Quantification of AQP9 in cerebrospinal fluid samples of HSE patients showed increment as compared to controls. We conclude that the olfactory route and the AC are important for the spread of HSV-1 within the olfactory/limbic system of rats and furthermore, we suggest that AQP9 is involved in viral tropism and pathogenesis of HSE.

Quorum sensing communication between bacteria and human cells: signals, targets, and functions

Both direct and long-range interactions between pathogenic Pseudomonas aeruginosa bacteria and their eukaryotic hosts are important in the outcome of infections. For cell-to-cell communication, these bacteria employ the quorum sensing (QS) system to pass on information of the density of the bacterial population and collectively switch on virulence factor production, biofilm formation, and resistance development. Thus, QS allows bacteria to behave as a community to perform tasks which would be impossible for individual cells, e.g., to overcome defense and immune systems and establish infections in higher organisms. This review highlights these aspects of QS and our own recent research on how P. aeruginosa communicates with human cells using the small QS signal molecules N-acyl homoserine lactones (AHL). We focus on how this conversation changes the behavior and function of neutrophils, macrophages, and epithelial cells and on how the signaling machinery in human cells responsible for the recognition of AHL. Understanding the bacteria-host relationships at both cellular and molecular levels is essential for the identification of new targets and for the development of novel strategies to fight bacterial infections in the future.