Satellite Glial Cells and Neurons in Trigeminal Ganglia Are Altered in an Itch Model in Mice.

Itch (pruritus) is a common chronic condition with a lifetime prevalence of over 20%. The mechanisms underlying itch are poorly understood, and its therapy is difficult. There is recent evidence that following nerve injury or inflammation, intercellular communications in sensory ganglia are augmented, which may lead to abnormal neuronal activity, and hence to pain, but there is no information whether such changes take place in an itch model. We studied changes in neurons and satellite glial cells (SGCs) in trigeminal ganglia in an itch model in mice using repeated applications of 2,4,6-trinitro-1-chlorobenzene (TNCB) to the external ear over a period of 11 days. Treated mice showed augmented scratching behavior as compared with controls during the application period and for several days afterwards. Immunostaining for the activation marker glial fibrillary acidic protein in SGCs was greater by about 35% after TNCB application, and gap junction-mediated coupling between neurons increased from about 2% to 13%. The injection of gap junction blockers reduced scratching behavior, suggesting that gap junctions contribute to itch. Calcium imaging studies showed increased responses of SGCs to the pain (and presumed itch) mediator ATP. We conclude that changes in both neurons and SGCs in sensory ganglia may play a role in itch.

Restrictions that control herpes simplex virus type 1 infection in mouse brain ex vivo.

Elucidating the cellular and molecular factors governing herpes simplex virus type 1 (HSV-1) neurotropism is a prerequisite for understanding HSV-1 encephalitis and for targeting HSV-1-derived vectors for gene transfer to the brain. Earlier we had described an ex vivo system of mouse brain slices and demonstrated a selective and unique infection pattern, mostly around the ventricles. Here, we examined tissue factors controlling HSV-1 infection of brain slices. We demonstrated that heparan sulphate, while an important factor, does not determine the infection pattern. Hyaluronic acid, but not collagen, appears to enhance HSV-1 brain infection. To investigate whether tissue distribution of viral receptors determines the infection pattern, we examined transcription of herpes virus entry mediator and nectin-1 receptor genes in infected and uninfected brain regions. Both the infected and the uninfected regions express the receptors. We also explored the influence of intra-cellular factors. HSV-1 does not preferentially infect proliferating cells in the brain slices, despite its predilection to the ventricular zones. To delineate the step at which the HSV-1 infection cascade is restricted, mRNA was isolated following tissue infection, and transcription of the immediate-early and late viral genes was evaluated. The results indicated that HSV-1 genes are not expressed in regions that do not express a viral reporter gene. Therefore, we conclude that tissue resistance to infection is associated with a block at or prior to the immediate-early mRNA synthesis. Taken together, using the ex vivo system of organotypic culture we describe here extra-cellular and intra-cellular restriction levels of HSV-1 brain infection.

Evolution of p53 in hypoxia-stressed Spalax mimics human tumor mutation.

The tumor suppressor gene p53 controls cellular response to a variety of stress conditions, including DNA damage and hypoxia, leading to growth arrest and/or apoptosis. Inactivation of p53, found in 40-50% of human cancers, confers selective advantage under hypoxic microenvironment during tumor progression. The mole rat, Spalax, spends its entire life cycle underground at decidedly lower oxygen tensions than any other mammal studied. Because a wide range of respiratory adaptations to hypoxic stress evolved in Spalax, we speculated that it might also have developed hypoxia adaptation mechanisms analogous to the genetic/epigenetic alterations acquired during tumor progression. Comparing Spalax with human and mouse p53 revealed an arginine (R) to lysine (K) substitution in Spalax (Arg-174 in human) in the DNA-binding domain, identical to known tumor associated mutations. Multiple p53 sequence alignments with 41 additional species confirmed that Arg-174 is highly conserved. Reporter assays uncovered that Spalax p53 protein is unable to induce apoptosis-regulating target genes, resulting in no expression of apaf1 and partial expression of puma, pten, and noxa. However, cell cycle arrest and p53 stabilization/homeostasis genes were overactivated by Spalax p53. Lys-174 was found critical for apaf1 expression inactivation. A DNA-free p53 structure model predicts that Arg-174 is important for dimerization, whereas Spalax Lys-174 prevents such interactions. Similar neighboring mutations found in human tumors favor growth arrest rather than apoptosis. We hypothesize that, in an analogy with human tumor progression, Spalax underwent remarkable adaptive p53 evolution during 40 million years of underground hypoxic life.