Ahmad Azlina

Potential Down-Regulation of Salivary Gland AQP5 by LPS via Cross-Coupling of NF-κB and p-c-Jun/c-Fos

The mRNA and protein levels of aquaporin (AQP)5 in the parotid gland were found to be potentially decreased by lipopolysaccharide (LPS) in vivo in C3H/HeN mice, but only weakly in C3H/HeJ, a TLR4 mutant mouse strain. In the LPS-injected mice, pilocarpine-stimulated saliva production was reduced by more than 50%. In a tissue culture system, the LPS-induced decrease in the AQP5 mRNA level was blocked completely by pyrrolidine dithiocarbamate, MG132, tyrphostin AG126, SP600125, and partially by SB203580, which are inhibitors for IkappaB kinase, 26S proteasome, ERK1/2, JNK, and p38 MAPK, respectively. In contrast, the expression of AQP1 mRNA was down-regulated by LPS and such down-regulation was blocked only by SP600125. The transcription factors NF-kappaB (p65 subunit), p-c-Jun, and c-Fos were increased by LPS given in vivo, whereas the protein-binding activities of the parotid gland extract toward the sequences for NF-kappaB but not AP-1-responsive elements present at the promoter region of the AQP5 gene were increased by LPS injection. Co-immunoprecipitation by using antibody columns suggested the physical association of the three transcription factors. These results suggest that LPS-induced potential down-regulation of expression of AQP5 mRNA in the parotid gland is mediated via a complex(es) of these two classes of transcription factors, NF-kappaB and p-c-Jun/c-Fos.

Effect of 940 nm low-level laser therapy on osteogenesis in vitro

Abstract. Bone regeneration is essential in medical treatment, such as in surgical bone healing and orthodontics. The aim of this study is to examine the effect of different powers of 940 nm diode low-level laser treatment (LLLT) on osteoblast cells during their proliferation and differentiation stages. A human fetal osteoblast cell line was cultured and treated with LLLT. The cells were divided into experimental groups according to the power delivered and periods of exposure per day for each laser power. The (3-(4,5-dimethylthiazol-2yl)-2,5 diphenyl tetrazolium bromide) (MTT) assay was used to determine cell proliferation. Both alkaline phosphatase and osteocalcin activity assays were assessed for cell differentiation. All treatment groups showed a significant increase in cell proliferation and differentiation compared to the control group. Regarding the exposure time, the subgroups treated with the LLLT for 6 min showed higher proliferation and differentiation rates for the powers delivered, the 300-mW LLLT group significantly increased the amount of cell proliferation. By contrast, the 100 and 200 mW groups showed significantly greater amounts of cell differentiation. These results suggest that the use of LLLT may play an important role in stimulating osteoblast cells for improved bone formation.

Novel phosphorylation of aquaporin-5 at its threonine 259 through cAMP signaling in salivary gland cells

Aquaporin-5 (AQP5), a water channel, plays key roles in salivary secretion. The novel phosphorylation of AQP5 was investigated by using human salivary gland (HSG) cells and mouse salivary glands. In the HSG cells stably transfected with a wild-type mouse AQP5 construct, a protein band immunoreactive with antibody against phosphorylated PKA substrate was detected in the AQP5 immunoprecipitated sample, and its intensity was enhanced by short-term treatment of the cells with 8-bromo-cAMP, forskolin, or phorbol 12-myristate 13-acetate, but not by that with A23187 calcium ionophore. Such enhancement was inhibited in the presence of H-89, a PKA inhibitor. An AQP5 mutant (AQP5-T259A) expressed by transfection of HSG cells was not recognized by anti-phosphorylated PKA substrate antibody, even when the cells were stimulated with the protein kinase activators. Immunoblotting and immunofluorescence studies using a specific antibody detecting AQP5 phosphorylated at its Thr259 demonstrated that AQP5 was rapidly and transiently phosphorylated at the apical membrane of acinar cells in the submandibular and parotid glands after administration of isoproterenol, but not pilocarpine. Furthermore, both AQP5 and AQP5-T259A were constitutively localized at the plasma membrane in HSG cells under the resting and forskolin-stimulated conditions. These results suggest that AQP5 is phosphorylated at its Thr259 by PKA through cAMP, but not Ca(2+), signaling pathways, and that this phosphorylation does not contribute to AQP5 trafficking in the salivary gland cells.

Inhibition and transcriptional silencing of a subtilisin-like proprotein convertase, PACE4/SPC4, reduces the branching morphogenesis of and AQP5 expression in rat embryonic submandibular gland

The submandibular gland (SMG) develops through the epithelial-mesenchymal interaction mediated by many growth/differentiation factors including activin and BMPs, which are synthesized as inactive precursors and activated by subtilisin-like proprotein convertases (SPC) following cleavage at their R-X-K/R-R site. Here, we found that Dec-RVKR-CMK, a potent inhibitor of SPC, inhibited the branching morphogenesis of the rat embryonic SMG, and caused low expression of a water channel AQP5, in an organ culture system. Dec-RVKR-CMK also decreased the expression of PACE4, a SPC member, but not furin, another SPC member, suggesting the involvement of PACE4 in the SMG development. Heparin, which is known to translocate PACE4 in the extracellular matrix into the medium, and an antibody specific for the catalytic domain of PACE4, both reduced the branching morphogenesis and AQP5 expression in the SMG. The inhibitory effects of Dec-RVKR-CMK were partially rescued by the addition of recombinant BMP2, whose precursor is one of the candidate substrates for PACE4 in vivo. Further, the suppression of PACE4 expression by siRNAs resulted in decreased expression of AQP5 and inhibition of the branching morphogenesis in the present organ culture system. These observations suggest that PACE4 regulates the SMG development via the activation of some growth/differentiation factors.

Degradation of submandibular gland AQP5 by parasympathetic denervation of chorda tympani and its recovery by cevimeline, an M3 muscarinic receptor agonist

By chorda tympani denervation (CTD, parasympathectomy), the aquaporin 5 (AQP5), but not AQP1, protein level in the rat submandibular gland (SMG) was significantly decreased, dropping to 37% of that of the contralateral gland at 4 wk. The protein levels of AQP5 and AQP1 were not significantly affected by denervation of the cervical sympathetic trunk (sympathectomy). Administration of cevimeline hydrochloride, an M3 muscarinic receptor agonist (10 mg/kg for 7 days po), but not pilocarpine (0.3 mg/kg for 7 days po), recovered the AQP5 protein level reduced by CTD and increased the AQP1 protein level above the control one. The mRNA level of AQP5 was scarcely affected by CTD and cevimeline hydrochloride administration. Administration of chloroquine (50 mg/kg for 7 days po), a denaturant of lysosomes, increased the AQP5 protein level reduced by CTD. An extract obtained from the submandibular lysosomal fraction degraded the AQP5 protein in the total membrane fraction in vitro. These results suggest the possible regulation of the AQP5 protein level in the SMG by the parasympathetic nerves/M3 muscarinic receptor agonist and imply the involvement of lysosomal enzymes, but not a transcriptional mechanism, in this regulation.

Roles of lysosomal proteolytic systems in AQP5 degradation in the submandibular gland of rats following chorda tympani parasympathetic denervation

Chorda tympani denervation (CTD) of rats was earlier shown to result in loss of submandibular gland (SMG) weight (at only 1 wk) and in continued reduction in aquaporin 5 (AQP5) protein expression (until 4 wk), without affecting its mRNA synthesis (Li X, Azlina A, Karabasil MR, Purwanti N, Hasegawa T, Yao C, Akamatsu T, Hosoi K. Am J Physiol Gastrointest Liver Physiol 295: G112-G123, 2008). The present study indicated that despite elevation of bax, a proapoptosis protein, by CTD, the operation also increased the level of bcl-2, an antiapoptosis protein, in the SMG. Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL assay) showed no increase in the number of apoptotic cells in the SMG. CTD, however, induced strongly and transiently (at 1-3 days) the protein expression of LC3B-II, a marker protein of autophagosomes, suggesting that the reduction in the gland weight was due to onset of autophagy by CTD. Upon CTD, Lamp2, a lysosomal marker, gradually increased in amount, reaching a peak at the 14th day. Immunohistochemical analysis revealed an increase in the number of lysosome-like structures positive for both AQP5 and Lamp2 in the acinar cells of the SMG after CTD; similar changes were observed also for AQP5 and LC3Bs. These data suggest that AQP5 in the SMG entered autophagosomes and/or lysosomes for degradation upon CTD. In vitro AQP5-degrading activity was found in the SMG extracts, and such activity was shown to be increased by CTD. Inhibitor experiments implied cathepsins B and L to be candidate enzymes for this degradation under normal and CTD conditions, respectively.

Effects of naturally occurring G103D point mutation of AQP5 on its water permeability, trafficking and cellular localization in the submandibular gland of rats

Background information. AQPs (aquaporins) are water channel proteins that are expressed in almost all living things. In mammalians, 13 members of AQPs (AQP0–12) have been identified so far. AQP5 is known to be expressed mostly in the exocrine cells, including the salivary gland acinar cells. A naturally occurring point mutation (G308A, Gly103 > Asp103) was earlier found in the rat AQP5 gene [Murdiastuti, Purwanti, Karabasil, Li, Yao, Akamatsu, Kanamori and Hosoi (2006) Am. J. Physiol. 291, G1081–G1088]; in this mutant, the rate of initial saliva secretion under stimulated and unstimulated conditions is less than that for the wt (wild‐type) animals.

Induction of Sca-1 in the duct cells of the mouse submandibular gland by obstruction of the main excretory duct.

The effect of ligation of the main excretory duct (MED) of the mouse submandibular gland (SMG) on the expression of Sca-1, a stem cell antigen, was examined by Western blotting and immunohistochemistry. By Western blotting, the expression of Sca-1 with a molecular weight of 18 kDa was identified in the normal gland. At 1 day post-ligation, the expression level of Sca-1 was strongly increased in the experimental gland and weakly in the contralateral gland, and such expression in both glands decreased at 6 days. By immunohistochemistry, Sca-1 was detected weakly in the apical membrane of excretory duct (ED) cells of the SMG under the normal condition. By duct ligation, Sca-1 became expressed strongly in most cells of the two major duct systems, i.e., the striated duct (SD) and granular convoluted tubules (GCT), but was not detected in the acinar (Ac) cells. By fluorescence-activated cell sorter (FACS) analysis, the number of side population (SP) cells in this gland was found to be increased by ligation. These results imply that Sca-1-positive cells may have a role in the duct cell proliferation in the regeneration step elicited by MED ligation-induced injury.

Induction of Sca-1 via activation of STAT3 system in the duct cells of the mouse submandibular gland by ligation of the main excretory duct.

To examine the very initial step that takes place immediately after tissue injury and is linked to tissue regeneration, we employed the submandibular gland (SMG), which was injured by ligation of its main excretory duct (MED). Ligation of the MED of the SMG in mice induced the expression of Sca-1, a protein marker of hematopoietic stem cells. In the normal gland, a low level of Sca-1 was expressed, which was localized predominantly in the excretory duct cells. At 1 day after ligation, Sca-1 expression increased prominently in almost all of cells in the duct system, but not in the acinar cells. The level of Sca-1 mRNA had begun to increase at 6 h after ligation and continuously rose thereafter until it reached a plateau, which occurred ∼12 h after ligation. STAT3 phosphorylated at its tyrosine-705 (p-STAT3) in the ligated gland increased immediately after ligation, and it was localized in the nuclei of all duct cells. The results of an EMSA revealed the specific binding of a nuclear extract to the sequence of the γ-interferon activation site (GAS) present in the Sca-1 promoter and confirmed that such binding increased after ligation. Thus the present study suggests that STAT3, having been phosphorylated following MED ligation, was transferred to the nucleus, where it bound to the GAS element in the promoter of Sca-1 gene, resulting in promotion of Sca-1 gene expression. Actual prevention of STAT3 phosphorylation reduced the ligation-induced Sca-1 elevation.

Lipopolysaccharide-Mediated Induction of Calprotectin in the Submandibular and Parotid Glands of Mice

S100A8 and S100A9 constitute a heterodimeric protein, calprotectin. The mRNAs of S100A8 and S100A9, being expressed at minimal levels in the submandibular and parotid glands (SMG and PG, respectively) of C3H/HeN mice, were induced strongly and transiently by lipopolysaccharide (LPS). Among the mRNAs of members of the S100 protein family examined, those of S100A8 and S100A9 were specifically induced by LPS in the salivary glands. The induction was assumed to be mediated via toll-like receptor 4 (TLR4), since their elevation was limited in C3H/HeJ mice, a TLR4-mutant strain. These proteins became expressed in the granular convoluted tubular cells and striated duct cells in the SMG, and in both acinar and duct cells in the PG (all in the cytoplasm). The salivary calprotectin level was not increased by LPS treatment, implying that elevated calprotectin was not secreted into the saliva and that they may function in microcellular environment of the salivary gland.