Toward gene therapy for growth hormone deficiency via salivary gland expression of growth hormone.

OBJECTIVES: Salivary glands are useful targets for gene therapeutics. After gene transfer into salivary glands, regulated secretory pathway proteins, such as human growth hormone, are secreted into saliva, whereas constitutive secretory pathway proteins, such as erythropoietin, are secreted into the bloodstream. Secretion of human growth hormone (hGH) into the saliva is not therapeutically useful. In this study, we attempted to redirect the secretion of transgenic hGH from the saliva to the serum by site-directed mutagenesis. MATERIALS AND METHODS: We tested hGH mutants first in vitro with AtT20 cells, a model endocrine cell line that exhibits polarized secretion of regulated secretory pathway proteins. Selected mutants were further studied in vivo using adenoviral-mediated gene transfer to rat submandibular glands. RESULTS: We identified two mutants with differences in secretion behavior compared to wild-type hGH. One mutant, ΔN1-6 , was detected in the serum of transduced rats, demonstrating that expression of this mutant in the salivary gland resulted in its secretion through the constitutive secretory pathway. CONCLUSION: This study demonstrates that mutagenesis of therapeutic proteins normally destined for the regulated secretory pathway may result in their secretion via the constitutive secretory pathway into the circulation for potential therapeutic benefit.

Immunomodulatory and potential therapeutic role of mesenchymal stem cells in periodontitis.

Periodontitis is a chronic inflammatory disease leading to alveolar bone destruction, and eventually tooth loss. In genetically or environmentally predisposed individuals periodontopathogenic bacteria trigger an inflammatory immune response where activated macrophages secrete inflammatory cytokines and T helper 17 cells produce interleukin-17, receptor activator of nuclear factor kappa B ligand (RANKL) and tumor necrosis factor-α. Inflammation and the production of RANKL, the key cytokine responsible for osteoclast activation, cause excessive activation of osteoclasts. This results in a decoupling between bone formation and resorption, leading to bone loss. As conventional treatment does not target the inflammatory response and osteoclast activation, its effectiveness is limited. Novel treatments are thus required if we are to cure this disease. Mesenchymal stem cells (MSCs), including those of dental origin, are potent immunomodulators and are known to be suitable for tissue regeneration. MSCs can inhibit the immune response by suppressing T cells, inducing regulatory T cells and converting dendritic cells and macrophages into a regulatory phenotype. Additionally, genetic modulation may enhance the therapeutic potential of MSCs. In the present review the authors describe the potential use of MSCs, either unmodified or engineered for therapeutic purposes in periodontitis, with special emphasis on MSCs from dental pulp and periodontal ligament. The paper envisions that multiple targeting of this inflammatory disease by modulating the immune response, promoting bone regeneration and inhibiting bone resorption might yield significantly improved treatment outcomes when combined with conventional treatment modalities.

Differentiation potential of stem cells from human dental origin - promise for tissue engineering.

Recent studies have revealed the existence of stem cells in various human tissues including dental structures. We aimed to establish primary cell cultures from human dental pulp and periodontal ligament, to identify multipotential adult stem cells in these cultures, and to study the differentiation capacity of these cells to osteogenic and to neuronal fates. Dental pulp and the periodontal ligament were isolated from extracted human wisdom teeth. The extracellular matrix was enzymatically degraded to obtain isolated cells for culturing. Both dental pulp and periodontal ligament derived cultures showed high proliferative capacity and contained a cell population expressing the STRO-1 mesenchymal stem cell marker. Osteogenic induction by pharmacological stimulation resulted in mineralized differentiation as shown by Alizarin red staining in both cultures. When already described standard neurodifferentiation protocols were used, cultures exhibited only transient neurodifferentiation followed by either redifferentiation into a fibroblast-like phenotype or massive cell death. Our new three-step neurodifferentiation protocol consisting of (1) epigenetic reprogramming, then (2) simultaneous PKC/PKA activation, followed by (3) incubation in a neurotrophic medium resulted in robust neurodifferentiation in both pulp and periodontal ligament cultures shown by cell morphology, immunocytochemistry and real time PCR for vimentin and neuron-specific enolase. In conclusion, we report the isolation, culture and characterization of stem cell containing cultures from both human dental pulp and periodontal ligament. Furthermore, our data clearly show that both cultures differentiate into mineralized cells or to a neuronal fate in response to appropriate pharmacological stimuli. Therefore, these cells have high potential to serve as resources for tissue engineering not only for dental or bone reconstruction, but also for neuroregenerative treatments.

Vectorial bicarbonate transport by Par-C10 salivary cells.

Salivary glands produce a HCO(3)(-)-rich fluid that is important for the neutral milieu in the upper gastrointestinal tract. The molecular mechanism of this secretion is poorly understood. Par-C10, an immortalized rat parotid acinar line, has been shown to secrete Cl(-)- in response to Ca(2+-)-mobilizing stimuli. Our aim was to assess the capacity of polarized monolayers of Par-C10 cells to transport and secrete HCO(3)(-)-. Transepithelial electrolyte movement was evaluated by short-circuit current measurements. Intracellular pH (pH(i)) was measured by microfluorometry in cells loaded with BCECF. Monolayers of Par-C10 cells, grown on Transwell membranes, developed high transepithelial resistance and exhibited vectorial anion secretion which was activated by both ATP and forskolin. The currents were partially inhibited by bumetanide and by withdrawal of HCO(3)(-) indicating the dependence of ion movements on NKCC and on HCO(3)(-) ions, respectively. In HCO(3)(-)-free solutions the recovery of pH(i) from acid loading was abolished by EIPA. In the presence of HCO(3)(-) there was a strong EIPA-insensitive recovery from acid loading which was inhibited by H(2)DIDS. ATP and forskolin stimulated HCO(3)(-) efflux from the cells. Furthermore, HCl(-) withdrawal experiments showed the presence of DNDS-sensitive basolateral anion exchange. In conclusion Par-C10 cells achieve transepithelial transport that is sensitive to both intracellular Ca(2+)- and cAMP-dependent stimulation. We identified Na(+)/H(+) exchange, Na(+)-HCO(3)(-) cotransport and anion exchange at the basolateral side of the cells as being involved in intracellular pH regulation and vectorial HCO(3)(-) secretion. This cell line offers a good model for further studies to understand the molecular mechanisms of salivary HCO(3)(-) secretion.

Distribution of aquaporin water channels AQP1 and AQP5 in the ductal system of the human pancreas.

BACKGROUND: The exocrine pancreas secretes large volumes of isotonic fluid, most of which originates from the ductal system. The role of aquaporin (AQP) water channels in this process is unknown. METHODS: Expression and localisation of known AQP isoforms was examined in normal human pancreas, pancreatic adenocarcinoma, and pancreatic cell lines of ductal origin (Capan-1, Capan-2, and HPAF) using reverse transcriptase-polymerase chain reaction and immunohistochemistry. RESULTS: Messenger RNAs for AQP1, -3, -4, -5, and -8 were detected in normal pancreas and in pancreatic adenocarcinoma. The cell lines expressed AQP3, -4, and -5 but lacked AQP1 and AQP8. Immunohistochemistry of normal pancreas revealed that AQP1 is strongly expressed in centroacinar cells and in both the apical and basolateral domains of intercalated and intralobular duct epithelia. AQP1 expression declined with distance along the small interlobular ducts and was not detectable in larger interlobular ducts. AQP3 and AQP4 were not detectable by immunohistochemistry. AQP5 was observed at the apical membrane of intercalated duct cells and also in duct associated mucoid glands. AQP8 was confined to the apical pole of acinar cells. Both AQP1 and AQP5 were colocalised with cystic fibrosis transmembrane conductance regulator (CFTR) at the apical membrane of intercalated duct cells. CONCLUSIONS: AQP1 and AQP5 are strongly expressed in the intercalated ducts of the human pancreas. Their distribution correlates closely with that of CFTR, a marker of ductal electrolyte secretion. This suggests that fluid secretion is concentrated in the terminal branches of the ductal tree and that both AQP1 and AQP5 may play a significant role.

Extracellular calcium sensing receptor in human pancreatic cells.

BACKGROUND AND AIMS: The extracellular calcium sensing receptor (CaR) plays a key role in the calcium homeostatic system and is therefore widely expressed in tissues involved in calcium metabolism. However, the CaR has also been identified in other tissues where its role is less clear. We have investigated the presence of the CaR in the human pancreas. METHODS: Messenger RNA for the CaR was detected by reverse transcription-polymerase chain reaction and the protein was localised by immunostaining. CaR function was assayed in Capan-1 cells by measuring intracellular calcium and [(3)H] thymidine incorporation. RESULTS: The receptor was highly expressed in human pancreatic ducts. It was also expressed in exocrine acinar cells, in islets of Langerhans, and in intrapancreatic nerves and blood vessels. The CaR was expressed in both normal and neoplastic human tissue samples but was detected in only one of five ductal adenocarcinoma cells lines examined. Experiments on the CaR expressing adenocarcinoma cell line Capan-1 showed that the CaR was functional and was linked to mobilisation of intracellular calcium. Stimulation of the CaR reduced Capan-1 cell proliferation. CONCLUSIONS: We propose that the CaR may play multiple functional roles in the human pancreas. In particular, the CaR on the duct luminal membrane may monitor and regulate the Ca(2+) concentration in pancreatic juice by triggering ductal electrolyte and fluid secretion. This could help to prevent precipitation of calcium salts in the duct lumen. The CaR may also help to regulate the proliferation of pancreatic ductal cells.