Synthesis, localization and possible function of serine (or cysteine) peptidase inhibitor, clade B, member 6a (Serpinb6a) in mouse submandibular gland

Decrease in alpha-1 antiproteinase antitrypsin is observed in primary Sjogren's syndrome condition

Primary Sjogren's syndrome (pSS) is a systemic autoimmune disease that is characterized by the infiltration of immune cells. Although the loss of salivary gland function is a major manifestation observed in pSS, the factors that could promote these changes in salivary gland tissue in pSS is not yet determined. Herein, we provide evidence that loss of alpha-1 antiproteinase antitrypsin could contribute to the induction of pSS. Alpha-1 antiproteinase antitrypsin belongs to the family of serpin proteins that function as protease inhibitors and protect secretory cells against proteases, especially to elastases that is secreted from lymphocytes. Importantly, expression of alpha-1 antiproteinase antitrypsin was decreased (more than 3-fold), along with an increase in elastase expression, in pSS samples when compared with age-matched non-SS-SICCA patients. Consistent with the human data, loss of alpha-1 antiproteinase antitrypsin, as well as an increase in immune infiltration, was observed in IL14α transgenic mice that exhibit SS like symptoms. Moreover, an age-dependent increase in elastase expression was observed in IL14α transgenic mice along with a decrease in total saliva secretion. Importantly, a 4-fold increase in microRNA132 expression, but not in other microRNAs, and increased DNA methylation in the promoter/noncoding region of serpina gene was observed in pSS, which could be responsible for the inhibition of alpha-1 antiproteinase antitrypsin expression in salivary gland cells of pSS patients. Together, these findings demonstrate that epigenetic regulations that include DNA methylation and microRNAs that could modulate the expression of alpha-1 antiproteinase antitrypsin in salivary glands and could be involved in the onset of pSS.

The lack of terminal tubule cells in the submandibular gland of mice deficient in submandibular gland protein C

The submandibular gland (SMG) of newborn mice has no mature acini but has the rudiments of acini called terminal tubules (TT). The TT are composed of TT cells with dark secretory granules and proacinar cells with lighter secretory granules, the latter being considered the immediate precursor of mature acinar cells. TT cells contain a specific secretory protein, submandibular gland protein C (SMGC) and they decrease in number postnatally at a higher rate in males than in females. In the present study, in order to clarify the biological roles of TT cells and their secretory product SMGC, we generated a knockout (KO) mouse strain deficient in SMGC. The KO mice of both sexes grew normally, had normal reproductive capacity and had normal acinar and duct systems in the SMG in adult ages. However, through the neonatal and early postnatal stages, the KO mice were deficient not only in the production of SMGC but also in TT cells. With electron microscopy of the SMG of newborn KO mice, TT cells with characteristic granules were absent and replaced by undifferentiated ductal cells, whereas proacinar cells were normal. These results suggested that the absence of SMGC inhibits the development of TT cells and that the absence of SMGC and TT cells has no notable influence on the postnatal development of the acinar and duct systems in the SMG.

Expression and localization of phosphodiesterase 2A in the submandibular gland of mice

OBJECTIVES

Phosphodiesterases comprise a superfamily of enzymes that hydrolyze and inactivate cyclic AMP (cAMP) and/or cyclic GMP (cGMP), thereby regulating cellular signaling mechanisms. We herein investigated the production of phosphodiesterase 2A (PDE2A) in the mouse submandibular gland.

DESIGN

The expression and localization of the mRNA and protein of PDE2A were examined in the submandibular gland of male and female mice using the reverse transcription-polymerase chain reaction, in situ hybridization, Western blotting, and immunohistochemistry.

RESULTS

Among the different species of phosphodiesterases examined in the mouse submandibular gland, PDE2A, which hydrolyzes cAMP and cGMP, exhibited a marked sexual difference; it was more abundantly expressed in females. The mRNA and protein signals for PDE2A were intense in all acinar and duct portions, including the striated duct, in females, whereas in males, these signals were markedly weaker in the granular convoluted duct, the counterpart of the female striated duct, than in acini and other duct portions. Furthermore, the signals for protein kinases A and G1, which are intracellular effectors of cAMP and cGMP, respectively, were markedly weaker in the male granular convoluted duct.

CONCLUSIONS

These results suggest that cyclic nucleotide-dependent signaling mechanisms function poorly in granular convoluted duct cells in the mouse submandibular gland.