Changes in the number and distribution of myoepithelial cells in the rat parotid gland during postnatal development

Characterization of the myoepithelial cells in the major salivary glands of the fruit bat Artibeus jamaicensis

Bats constitute one of the most numerous mammalian species. Bats have a wide range of dietary habits and include carnivorous, haematophagous, insectivorous, frugivorous and nectivorous species. The salivary glands of these species have been of particular research interest due to their structural variability among chiropterans with different types of diets. Myoepithelial cells (MECs), which support and facilitate the expulsion of saliva from the secretory portions of salivary glands, are very important for their function; however, this cell type has not been extensively studied in the salivary glands of bats. In this study, we characterized the MECs in the major salivary glands of the fruit bat Artibeus jamaicensis. Herein, we describe the morphology of the parotid, submandibular and sublingual glands of A. jamaicensis at the light- and electro-microscopic level and the distribution of MECs in these glands, as defined by their expression of smooth-muscle markers such as α-smooth muscle actin (SMAα) and desmin, and of epithelial cell markers, such as KRT14. We found that the anatomical locations of the major salivary glands in this bat species are similar to those of humans, except that the bat sublingual gland appears to be unique, extending to join the contralateral homologous gland. Morphologically, the parotid gland has the characteristics of a mixed-secretory gland, whereas the submandibular and sublingual glands were identified as mucous-secretory glands. MECs positive for SMAα, KRT14 and desmin were found in all of the structural components of the three glands, except in their excretory ducts. Desmin is expressed at a lower level in the parotid gland than in the other glands. Our results suggest that the major salivary glands of A. jamaicensis, although anatomically and structurally similar to those of humans, play different physiological roles that can be attributed to the dietary habits of this species.

Exogenous thyroid hormone affects myoepithelium and proliferation in the developing rat parotid gland

In the mature rat parotid gland, myoepithelial cells (MEC) invest intercalated ducts, but not acini. During postnatal development, however, these cells differentiate around both intercalated ducts and acini, then translocate to only intercalated ducts during weaning. Previously, we found that thyroxine (T(4)) accelerates translocation of cells with small secretory granules from acini into intercalated ducts and the number of apoptotic cells increased tremendously with high doses. We present here additional analysis of the effects of T(4) on developing rat parotid gland, namely, the distribution of MEC and the proliferation of parenchymal cells. Beginning at age four days, pups were given daily subcutaneous injections of low, medium, and high doses of T(4) or vehicle or no injection. At ages 4, 7, 10, and 15 days, glands were excised and processed for light microscopy. Sections were double-immunostained with antibodies against proliferating cell nuclear antigen (PCNA) and actin, and counterstained with hematoxylin. Proliferative activity was assessed via PCNA histochemistry and MEC were identified using actin histochemistry. MEC in the T(4) groups invested mostly acini at 15 days in vehicle/normal glands and mostly intercalated ducts after 10 days in the T(4) groups. The proliferative activity of acinar cells and MEC in vehicle/normal glands declined progressively with age and T(4) increased the rate of this decline in the MEC in a dose-dependent manner. We conclude that T(4) accelerates the translocation of MEC from acini to intercalated ducts and that an important mechanism is the more rapid decline in the proliferative activity of MEC than in acinar cells in the T(4) groups. Some of the decline in the proliferative activity of all cells in the high and medium dose T(4) groups after seven days may have been due to dose-related thyroxine toxicity.

On approaches to the functional restoration of salivary glands damaged by radiation therapy for head and neck cancer, with a review of related aspects of salivary gland morphology and development

Radiation therapy for cancer of the head and neck can devastate the salivary glands and partially devitalize the mandible and maxilla. As a result, saliva production is drastically reduced and its quality adversely altered. Without diligent home and professional care, the teeth are subject to rapid destruction by caries, necessitating extractions with attendant high risk of necrosis of the supporting bone. Innovative techniques in delivery of radiation therapy and administration of drugs that selectively protect normal tissues can reduce significantly the radiation effects on salivary glands. Nonetheless, many patients still suffer severe oral dryness. I review here the functional morphology and development of salivary glands as these relate to approaches to preventing and restoring radiation-induced loss of salivary function. The acinar cells are responsible for most of the fluid and organic material in saliva, while the larger ducts influence the inorganic content. A central theme of this review is the extent to which the several types of epithelial cells in salivary glands may be pluripotential and the circumstances that may influence their ability to replace cells that have been lost or functionally inactivated due to the effects of radiation. The evidence suggests that the highly differentiated cells of the acini and large ducts of mature glands can replace themselves except when the respective pools of available cells are greatly diminished via apoptosis or necrosis owing to severely stressful events. Under the latter circumstances, relatively undifferentiated cells in the intercalated ducts proliferate and redifferentiate as may be required to replenish the depleted pools. It is likely that some, if not many, acinar cells may de-differentiate into intercalated duct-like cells and thus add to the pool of progenitor cells in such situations. If the stress is heavy doses of radiation, however, the result is not only the death of acinar cells, but also a marked decline in functional differentiation and proliferative capacity of all of the surviving cells, including those with progenitor capability. Restoration of gland function, therefore, seems to require increasing the secretory capacity of the surviving cells, or replacing the acinar cells and their progenitors either in the existing gland remnants or with artificial glands.

Comparison of proliferating cells between human adult and fetal eccrine sweat glands

Studies of sweat glands had demonstrated that there were degenerating cells and proliferating cells in the eccrine sweat glands. To compare the differences in the proliferating cells between human adult and fetal eccrine sweat glands, immunostaining of proliferating-associated proliferating cell nuclear antigen (PCNA) and Ki67 nuclear antigen (Ki67) was performed, and the location and the percentage of the positive staining cells were analyzed. The results showed that a few cells of the secretory and ductal portion in both the adult and fetal eccrine sweat glands stained positive with Ki67 and PCNA. The labeling index of PCNA in adult eccrine sweat glands was 34.71 +/- 8.37%, while that in the fetal was 62.72 +/- 6.54%. The labeling index of PCNA in fetal eccrine sweat glands was higher than that in adult. Myoepithelial cells were negative staining with anti-PCNA antibody in adult eccrine sweat glands, while in the fetal a few myoepithelial cells were positive staining. Labeling index of Ki67 in adult eccrine sweat glands was similar to that in the fetal, ranging from 0.5 to 4.3%. Myoepithelial cells of the adult and fetal eccrine sweat glands both were negative staining with anti-Ki67 antibody. We concluded that the myoepithelial cells had proliferating ability only in fetal eccrine sweat glands, and that the proliferating ability of fetal eccrine sweat glands was stronger than that of the adult.

Effects of exogenous thyroid hormone on the postnatal morphogenesis of the rat parotid gland

Administration of thyroid hormone has been shown to accelerate the early postnatal development of the rat parotid gland, but these studies have dwelt almost entirely on biochemical changes. The objective of this study was to describe the effects of exogenous thyroid hormone on morphologic aspects of the developing parotid gland, in particular the transient appearance of scattered mucous cells in this otherwise serous gland. Pups were given a daily subcutaneous injection of thyroxine (T(4)) of 0.1, 0.5, or 5.0 microg/g body weight, vehicle only (injection control), or no injection (normal control) beginning at 4 days, and killed for the collection of blood and parotid glands at intervals through 15 days. The serum was analyzed for T(4) and the glands were examined by light and electron microscopy. The results indicated that both serum T(4) and the pace of gland development were proportional to the dose of T(4). In particular, T(4) accelerated decreases in acinar size and gland area occupied by stroma and translocation of a subset of cells with small secretory granules, deeply stained with periodic acid-Schiff, from acini to intercalated ducts. However, the chronology of mucous cell disappearance was indifferent to treatment. In addition, signs of toxicity, including slower gain in body weight and greatly increased apoptosis and vacuoles in the glands, occurred with the higher doses of T(4).