TLR Signals in Epithelial Cells in the Nasal Cavity and Paranasal Sinuses

The respiratory tract is constantly at risk of invasion by microorganisms such as bacteria, viruses, and fungi. In particular, the mucosal epithelium of the nasal cavity and paranasal sinuses is at the very forefront of the battles between the host and the invading pathogens. Recent studies have revealed that the epithelium not only constitutes a physical barrier but also takes an essential role in the activation of the immune system. One of the mechanisms equipped in the epithelium to fight against microorganisms is the Toll-like receptor (TLR) response. TLRs recognize common structural components of microorganisms and activate the innate immune system, resulting in the production of a plethora of cytokines and chemokines in the response against microbes. As the epithelia-derived cytokines are deeply involved in the pathogenesis of inflammatory conditions in the nasal cavity and paranasal sinuses, such as chronic rhinosinusitis (CRS) and allergic rhinitis (AR), the molecules involved in the TLR response may be utilized as therapeutic targets for these diseases. There are several differences in the TLR response between nasal and bronchial epithelial cells, and knowledge of the TLR signals in the upper airway is sparse compared to that in the lower airway. In this review, we provide recent evidence on TLR signaling in the upper airway, focusing on the expression, regulation, and responsiveness of TLRs in human nasal epithelial cells (HNECs). We also discuss how TLRs in the epithelium are involved in the pathogenesis of, and possible therapeutic targeting, for CRS and AR.

β3 -adrenergic receptor activation plays an important role in the depressed myocardial contractility via both elevated levels of cellular free Zn2+ and reactive nitrogen species

Role of β₃ -AR dysregulation, as either cardio-conserving or cardio-disrupting mediator, remains unknown yet. Therefore, we examined the molecular mechanism of β₃ -AR activation in depressed myocardial contractility using a specific agonist CL316243 or using β₃ -AR overexpressed cardiomyocytes. Since it has been previously shown a possible correlation between increased cellular free Zn²⁺ ([Zn²⁺ ]_i ) and depressed cardiac contractility, we first demonstrated a relation between β₃ -AR activation and increased [Zn²⁺ ]_i , parallel to the significant depolarization in mitochondrial membrane potential in rat ventricular cardiomyocytes. Furthermore, the increased [Zn²⁺ ]_i induced a significant increase in messenger RNA (mRNA) level of β₃ -AR in cardiomyocytes. Either β₃ -AR activation or its overexpression could increase cellular reactive oxygen species (ROS) and reactive nitrogen species (RNS) levels, in line with significant changes in nitric oxide (NO)-pathway, including increases in the ratios of pNOS3/NOS3 and pGSK-3β/GSK-3β, and PKG expression level in cardiomyocytes. Although β₃ -AR activation induced depression in both Na⁺ - and Ca²⁺ -currents, the prolonged action potential (AP) seems to be associated with a marked depression in K⁺ -currents. The β₃ -AR activation caused a negative inotropic effect on the mechanical activity of the heart, through affecting the cellular Ca²⁺ -handling, including its effect on Ca²⁺ -leakage from sarcoplasmic reticulum (SR). Our cellular level data with β₃ -AR agonism were supported with the data on high [Zn²⁺ ]_i and β₃ -AR protein-level in metabolic syndrome (MetS)-rat heart. Overall, our present data can emphasize the important deleterious effect of β₃ -AR activation in cardiac remodeling under pathological condition, at least, through a cross-link between β₃ -AR activation, NO-signaling, and [Zn²⁺ ]_i pathways. Moreover, it is interesting to note that the recovery in ER-stress markers with β₃ -AR agonism in hyperglycemic cardiomyocytes is favored. Therefore, how long and to which level the β₃ -AR agonism would be friend or become foe remains to be mystery, yet.

Increased free Zn2+ correlates induction of sarco(endo)plasmic reticulum stress via altered expression levels of Zn2+ -transporters in heart failure

Zn²⁺ -homoeostasis including free Zn²⁺ ([Zn²⁺ ]_i ) is regulated through Zn²⁺ -transporters and their comprehensive understanding may be important due to their contributions to cardiac dysfunction. Herein, we aimed to examine a possible role of Zn²⁺ -transporters in the development of heart failure (HF) via induction of ER stress. We first showed localizations of ZIP8, ZIP14 and ZnT8 to both sarcolemma and S(E)R in ventricular cardiomyocytes (H9c2 cells) using confocal together with calculated Pearson's coefficients. The expressions of ZIP14 and ZnT8 were significantly increased with decreased ZIP8 level in HF. Moreover, [Zn²⁺ ]_i was significantly high in doxorubicin-treated H9c2 cells compared to their controls. We found elevated levels of ER stress markers, GRP78 and CHOP/Gadd153, confirming the existence of ER stress. Furthermore, we measured markedly increased total PKC and PKCα expression and PKCα-phosphorylation in HF. A PKC inhibition induced significant decrease in expressions of these ER stress markers compared to controls. Interestingly, direct increase in [Zn²⁺ ]_i using zinc-ionophore induced significant increase in these markers. On the other hand, when we induced ER stress directly with tunicamycin, we could not observe any effect on expression levels of these Zn²⁺ transporters. Additionally, increased [Zn²⁺ ]_i could induce marked activation of PKCα. Moreover, we observed marked decrease in [Zn²⁺ ]_i under PKC inhibition in H9c2 cells. Overall, our present data suggest possible role of Zn²⁺ transporters on an intersection pathway with increased [Zn²⁺ ]_i and PKCα activation and induction of HF, most probably via development of ER stress. Therefore, our present data provide novel information how a well-controlled [Zn²⁺ ]_i via Zn²⁺ transporters and PKCα can be important therapeutic approach in prevention/treatment of HF.