Adrenoceptor coupling mechanisms which regulate salivary secretion during aging

Current developments and opportunities of pluripotent stem cells-based therapies for salivary gland hypofunction

Salivary gland hypofunction (SGH) caused by systemic disease, drugs, aging, and radiotherapy for head and neck cancer can cause dry mouth, which increases the risk of disorders such as periodontitis, taste disorders, pain and burning sensations in the mouth, dental caries, and dramatically reduces the quality of life of patients. To date, the treatment of SGH is still aimed at relieving patients' clinical symptoms and improving their quality of life, and is not able to repair and regenerate the damaged salivary glands. Pluripotent stem cells (PSCs), including embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and extended pluripotent stem cells (EPSCs), are an emerging source of cellular therapies that are capable of unlimited proliferation and differentiation into cells of all three germ layers. In recent years, the immunomodulatory and tissue regenerative effects of PSCs, their derived cells, and paracrine products of these cells have received increasing attention and have demonstrated promising therapeutic effects in some preclinical studies targeting SGH. This review outlined the etiologies and available treatments for SGH. The existing efficacy and potential role of PSCs, their derived cells and paracrine products of these cells for SGH are summarized, with a focus on PSC-derived salivary gland stem/progenitor cells (SGS/PCs) and PSC-derived mesenchymal stem cells (MSCs). In this Review, we provide a conceptual outline of our current understanding of PSCs-based therapy and its importance in SGH treatment, which may inform and serve the design of future studies.

The effect of ageing on parenchymal cell populations in adult female mouse submandibular gland

The submandibular gland shows an array of responses that accompany ageing, which are usually modest. However, the submandibular acinar-cell mucin shows a substantial decline in total amount per gland. In the submandibular gland, there is also a loss of secretory parenchyma. A number of factors that could influence either parenchymal loss or a change in its cellular composition were examined in three ages of adult female mice. The goal was to see if there are ageing-related cellular changes that might have an effect on mucin production or secretion. The factors examined included DNA, protein, rates of cell division and apoptosis, cell volume and cellular composition of the parenchymal population. The parenchymal cell composition showed significant differences during ageing, with a substantial decrease in the percentage of acinar cells and increases in the percentage of both types of ductal cell components. This decline in the proportion of acinar cells in the parenchyma also reflected an overall reduction in the total number of acinar cells in the gland. Thus, the change in proportions of cells may potentially be a direct cause of the ageing-related decline in the submandibular acinar-cell mucin. The alteration in cellular composition was not attributable to changes in the cell-division indices; however, there was an increased rate of apoptosis for acinar cells that was significantly different between 3 and 28 months. The apoptotic rate doubled for acinar cells but showed no significant change in ductal cells. This selective change in the rate of apoptosis with ageing suggests that it is one of the main reasons for the decline in the proportion of acinar cells in the submandibular gland.

Partial restoration of impaired alpha 1-adrenergic responsiveness in parotid cells of aged rats by S-adenosylmethionine treatment

The age related decrease in alpha 1-adrenergic stimulated inositol 1, 4, 5 trisphosphate (IP3) production in parotid cells of aged rats can be partially restored by treatment with S-adenosylmethionine (SAM). This effect is completely blocked by S-adenosyl homocysteine (SAH) and occurs in association with an increase in the conversion of phosphatidylethanolamine to phosphatidylcholine and a decrease in membrane viscosity. In contrast, SAM treatment actually inhibits stimulated IP3 production in cells of young rats. The membrane viscosity of these cells is lower than that of those from aged rats. Although conversion of phosphatidylethanolamine to phosphatidylcholine is enhanced, no further decrease in membrane viscosity is elicited in young cell preparations. These findings suggest that age changes in the membrane environment may result in impaired alpha 1-adrenergic signal transduction and that such alterations may be at least partially reversible by SAM treatment.

Impaired expression of Gs alpha protein mRNA in rat ventricular myocardium with aging

We have recently reported that the responsiveness of adrenoceptors is decreased with aging in rat ventricular myocardium. Thus, the current study determined aging-dependent changes in: (a) characteristics of myocardial G proteins as determined by Western blot analysis; (b) steady-state levels of G protein mRNA as determined by Northern blot analysis; and (c) the intropic response to isoproterenol, a beta-adrenoceptor agonist. Cardiac preparations were isolated from male Wistar rats of 6 (adult) and 24 (old) months old. Compared with adults, aging decreased the combined level of the three Gs alpha subunits (45, 47 and 52 kDa) by a total of 23% in ventricular membrane preparations. In contrast, levels of Gi alpha (40/41 kDa), Gq alpha (42 kDa), Go alpha (39 kDa) and G common beta (35/36 kDa) immunoreactivity were not affected by aging in the same membrane preparations. In ventricular myocardium, steady-state levels of Gs alpha mRNA (1.9 kb) decreased by 20-28% between 6 and 24 months of age with no change in Gi alpha mRNA (2.4 kb). An aging-associated decline in beta-adrenergic stimulation was observed in the maximum positive inotropic effect elicited by isoproterenol in the presence of prazosin in left papillary muscles, with no change in ED50 values. These results suggest that age-related changes in cardiac excitation and contraction coupling following beta-adrenoceptor stimulation are mediated, at least in part, by Gs alpha protein dysfunction.