Microcephaly is the most prominent symptom of the developmental brain abnormalities induced by congenital cytomegalovirus (CMV) infection. To investigate the effect of CMV infection on neuronal migration in developing brains, mouse embryos on one side of uteri received, on day 15.5 of gestation (E15.5), an injection of murine CMV (MCMV) into the cerebral ventricles, and the embryos on the other side of the uteri were injected with minimum essential medium (MEM). Labeling with 5-bromo-2-deoxyuridine (BrdU) was accomplished by intraperitoneal injection of BrdU 6 h later. Disturbance of the neuronal migration and loss of neurons were observed postnatally in the brains of MCMV-infected mice, which were identified by immunohistochemical staining of viral antigen. Double staining of BrdU-labeled and viral antigen-positive cells in brains on the 7th postnatal day showed that the migration of BrdU-single-labeled cells, mainly localized in cerebral layers II-III, mostly preceded that of the viral antigen-positive cells. However, about 7.5% of the cells observed were double-labeled, especially in the layers III-IV, and a few double-stained cells were markedly disturbed in migration. In the brains of offspring labeled with BrdU 72 h after infection with MCMV on E15.5, most of the double-stained cells were seen around the ventricular and subventricular zones. These findings suggest that a disturbance of neuronal migration in addition to neuronal loss may play a crucial role in the development of microcephaly in congenital CMV infection in humans.

The susceptibility of mice at different developmental stages to a relatively low titer of cell culture-passaged murine cytomegalovirus (MCMV) infection was compared in terms of the urinary excretion of MCMV examined by plaque assay and in terms of the distribution of viral infection, determined by immunohistochemistry, using antibodies specific to the early nuclear antigen of MCMV. Viral infection on day 8.5 of gestation (E8.5) into the conceptus and intraperitoneal infection on day 15.5 of gestation (E15.5), postnatal day 2 (P2), postnatal day 11 (P11), and 30 days after birth (P30), respectively, were performed. Embryonal and perinatal mice were more susceptible to MCMV in terms of urinary excretion of the virus and the presence of viral antigen-positive cells in the brain, lungs, and kidneys. In the embryonal and perinatal infection, the viral antigen-positive cells in the neurons of the cerebral cortex and hippocampus were retained late after birth, even though the positive cells in the lungs and kidneys had disappeared. In the mice infected on E8.5, small clusters of viral antigen-positive cells were detected only in the cortex and hippocampus late after birth, without the urinary excretion of virus. These results suggest that when mice are infected with MCMV at the embryonal and perinatal stages, elimination of the infected neurons is delayed compared with that of the other cells in the lungs and kidneys. These findings provide a model for the analysis of pathogenesis of the subclinical congenital CMV infection that manifested clinically late after birth in humans as brain disorders.

Murine cytomegalovirus (MCMV), which causes acute, latent, and persistent infection of the natural host, is used as an animal model of human cytomegalovirus (HCMV) infection. Transcription of MCMV immediate-early (IE) genes is required for expression of the early and late genes and is dependent on host cell transcription factors. Cell-type-specific expression activity of the MCMV IE promoter was analyzed in transgenic mice generated with the major IE (MIE) enhancer/promoter involving nucleotides -1343 to -6 (1338 bp) connected to the reporter gene lacZ. Distinct expression was observed in the brain, kidneys, stomach, and skeletal muscles. Weak expression was observed in a portion of the parenchymal cells of the salivary glands and pancreas, and expression was hardly detected in the lungs, intestine, or immune and hematopoietic organs such as the thymus, spleen, lymph nodes, and bone marrow. The spectrum of organs positive for expression was narrower than that of the HCMV MIE promoter-lacZ transgenic mice reported previously and showed a greater degree of cell-type specificity. Interestingly, astrocyte-specific expression of the transgene was observed in the brain and primary glial cultures from the transgenic mice by combination of beta-galactosidase (beta-Gal) expression and immunostaining for cell markers. However, the transgene was not expressed in neurons, oligodendroglia, microglia, or endothelial cells. Furthermore, the beta-Gal expression in glial cultures was stimulated significantly by MCMV infection or by addition of calcium ionophore. These observations indicated that expression activity of the MCMV IE promoter is strictly cell-type specific, especially astrocyte-specific in the brain. This specific pattern of activity is similar to that of natural HCMV infection in humans.

Cytomegalovirus (CMV) is the most common cause of congenital infection, resulting in birth defects such as microcephaly. In this study, we found that apoptosis is induced in the developing mouse brain infected with murine cytomegalovirus (MCMV) in an association with neuronal cell loss. With the combination of the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) technique and immunohistochemical staining, 3.8% of the TUNEL-positive cells were double-stained with the antibody to neuron-specific enolase, while none of the TUNEL-positive cells were stained with antibodies to the immediate early and early viral antigens of MCMV. Furthermore, distribution pattern of the TUNEL-positive cells was different from that of viral DNA-positive cells detected by the in situ DNA-DNA hybridization. More than 30% of the TUNEL-positive cells were double-stained with the F4/80 antibody specific for microglia/macrophages, which were sometimes swollen, presumably the consequence of engulfment of the neuronal apoptotic cells. In the primary neuronal cultures, MCMV infection inhibited the induction of apoptosis either by serum deprivation or by glutamate treatment. It was also confirmed by the double-staining method that apoptosis was not induced in the viral-infected neuronal cultures. These results suggest that MCMV infection induces apoptosis in non-infected neuronal cells, presumably by indirect mechanisms, and that apoptotic cells are engulfed by microglia/macrophages. The induction and blocking of neuronal apoptosis by viral infection may be important for morphological and functional brain disorders in the congenital CMV infection.

This study shows that caspase 3 is important in the salivary dysfunction of SS, while caspase 9 appears not to be involved.

Objective Salivary gland epithelial cells in patients with Sjögren's syndrome (SS) and in NOD and NOD.scid mice express Fas and Fas ligand, and these cells die from apoptosis. To elucidate the intracellular molecular mechanisms responsible for this salivary gland epithelial cell apoptosis, expression of the Bcl‐2 family of proteins (Bcl‐2, Bcl‐xL, Bax) and caspase (caspases 3 and 8) was studied in young (ages 8–10 weeks) and old (ages 17–28 weeks) NOD and NOD.scid mice. Methods Sections of frozen salivary gland tissue were obtained from NOD and NOD.scid mice and from the lip biopsy material of SS patients. Immunohistochemistry or Western blot analysis was performed to assess the apoptotic‐associated proteins. Results Levels of Bax and caspase 3 were elevated in the epithelial cells of glands from old NOD mice, but not in those from young NOD mice. In contrast, epithelial cells from both young and old NOD.scid mice exhibited strong expression of Bax and caspase 3. Western blot analysis showed that the activated form of caspase 3 was increased 2–5‐fold in the glands from old NOD, old NOD.scid, and young NOD.scid mice compared with those from young NOD mice. Caspase 3 was also significantly elevated (P < 0.01) in SS patients whose focus scores were grade 3 or 4. In the SS patients' biopsy tissue and in the mouse glands, cells with fragmented DNA were positive for caspase 3. Conclusion These results demonstrate that salivary gland epithelial cells in NOD and NOD.scid mice overexpress the proapoptotic molecules Bax and caspase 3. Bax could be the gene responsible for initiation of caspase activation, epithelial cell destruction, and lymphocyte glandular localization in SS.

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Bax is an oncogene that has proapoptotic properties but not all cells that express Bax undergo apoptosis. Bax may have a function unrelated to apoptosis. To elucidate the role of Bax in cell signaling, an epithelial cell line called SMG-C6 was transfected with the human bax gene. Stable transfectants were studied for their response to carbachol, a muscarinic receptor agonist, by measuring the increase in intracellular free Ca 2+ and Ca 2+in¯ux. Carbachol-mediated release of Ca 2+ from intracellular stores was signi®cantly higher in Bax transfectants compared to control transfectants (empty vector). Ca 2+ in¯ux was also increased in Bax transfectants. Bax had no aect on the storage operated channels. However, the concentration of Ca 2+ in the intracellular stores (i.e., mitochondria and granules) was 40 ± 50% lower in the Bax transfectants. There was no signi®cant dierence in thapsigargin-mediated apoptosis in Bax transfectants compared to wild-type and control transfectants. Measurement of glutathione was reduced in the Bax transfectant. Restoration of glutathione levels with glutathione monoethyl ester partially normalized Ca 2+ mobilization and storage capacity in the mitochondria to control levels. This study shows that subapoptotic levels of Bax can reduce Ca 2+ content in intracellular stores and Ca 2+ homeostasis. Bax may mediate these eects by reducing the levels of antioxidants resulting in mild oxidative stress.