ABSTRACT
Alzheimer's disease (AD) is the most common cause of dementia in the elderly, characterized by progressive cognitive dysfunction. Aquaporin 9 (AQP9) is an aquaglyceroporin membrane channel shown biophysically to conduct water, glycerol, and other small solutes. In our study, we reported for the first time an age-associated decrease in AQP9 mRNA and protein expressions in both hippocampus and cerebral cortex of APPswe/PS1dE9 (Tg) AD mice at 3, 6 and 10â¯months of age. Consistently, we observed a dose-dependent downregulation of AQP9 expression in PC12 cells after treatment with amyloid-beta protein 1-40 (Aß1-40). Pre-treatment with AQP9 small interfering RNA led to a more severe neurotoxicity in PC12 cells in response to Aß1-40. Furthermore, we corroborated that the active participation of AQP9 in AD progression is associated with Aß-induced apoptosis both in vitro and in vivo. Taken together, our results reveal an important role of AQP9 in Aß-induced pathogenesis of AD which deserves further investigation.
Subject(s)
Alzheimer Disease/metabolism , Amyloid beta-Peptides/toxicity , Aquaporins/metabolism , Peptide Fragments/toxicity , Amyloid beta-Protein Precursor/metabolism , Animals , Apoptosis , Apoptosis Regulatory Proteins/metabolism , Brain-Derived Neurotrophic Factor/metabolism , Cell Survival , Cerebral Cortex/metabolism , Disease Models, Animal , Down-Regulation , Hippocampus/metabolism , In Vitro Techniques , Mice, Transgenic , PC12 Cells , RNA, Messenger/metabolism , RatsABSTRACT
Telomerase is an enzyme composed of a catalytic subunit (TERT) and RNA template (TR), which specifically elongates telomeres and prevents cellular senescence. Although telomerase cannot be detected in most human somatic tissues, including the nervous system, it can be detected in teleost tissues. To facilitate the investigation of telomerase function in the teleost visual system, the coding sequence of zebrafish TERT is revealed and cloned. Immunoblot, immunohistochemistry, reverse transcription polymerase chain reaction (RT-PCR), and telomeric repeats amplification protocol (TRAP) assay are used to assess the expression of telomerase at mRNA, protein, and functional levels in zebrafish retina. Based on the amino acid sequence of mouse TERT, a full-length telomerase reverse transcriptase cDNA of zebrafish has been isolated and cloned. The deduced protein sequence contains 1,091 amino acid residues and a predicted molecular mass of 126 kDa. Multiple alignment shows that the protein sequence contains the conserved motifs and residues found in TERT of other species. RT-PCR and TRAP assay has detected TERT mRNA expression and telomerase activity, respectively, in all tissues examined, including the retina and the brain. The presence of telomerase activity indicates that a fully functional form of telomerase can be found in the retina. Immunohistochemistry reveals that most neurons in zebrafish retina express TERT in the cell nucleus. The presence of telomerase in different tissues may be associated with the indeterminate growth of teleost. However, teleost retinal neurons are post-mitotic and do not further divide under normal situation. The expression of telomerase activity and TERT in retina implies that telomerase has functions other than the elongation of telomere. These findings could provide new insights on telomerase function in the nervous system.
Subject(s)
Telomerase/metabolism , Zebrafish Proteins/metabolism , Zebrafish/genetics , Amino Acid Sequence/genetics , Animals , Base Sequence/genetics , Brain/cytology , Brain/metabolism , Cell Differentiation/genetics , Cloning, Molecular , Conserved Sequence , Molecular Sequence Data , Molecular Weight , Neurons/metabolism , Phylogeny , RNA, Messenger/analysis , RNA, Messenger/genetics , RNA, Messenger/metabolism , Retina/cytology , Retina/metabolism , Sequence Homology, Amino Acid , Telomerase/genetics , Telomerase/isolation & purification , Zebrafish/growth & development , Zebrafish/metabolism , Zebrafish Proteins/genetics , Zebrafish Proteins/isolation & purificationABSTRACT
Schwann cells (SCs) are considered one of the major cellular components to maintain the integrity of the peripheral nervous system (PNS) neurons after injury. Intravitreal transplant of peripheral nerves or Schwann cells has been shown to enhance the regenerative ability of retinal ganglion cells (RGCs). In the present study, we compared the effects of intravitreal transplants of Schwann cells and fibroblasts, two major components of peripheral nerves, on the survival of retinal ganglion cells in adult rats after optic nerve (ON) transection. Purified Schwann cells and fibroblasts from neonatal sciatic nerves were injected into the vitreous body of adult rats. Three days after the injection, the optic nerves were transected intraorbitally. After 1 week or 1 month, surviving retinal ganglion cells were retrogradely labelled with Fluoro-Gold (FG) and the number of surviving retinal ganglion cells was counted. The retinas were further processed for 200-kDa neurofilament RT-97 immunohistochemistry. It was found that intravitreally injected- Schwann cells and -fibroblasts delayed the death of axotomized retinal ganglion cells for 1 week. In addition, in the animal group with 1 month survival time after optic nerve transection, those received a larger number of Schwann cells had more surviving retinal ganglion cells and more profusely ramified axonal processes near the optic disc. These findings reveal that both Schwann cells and fibroblasts isolated from the peripheral nerve can promote retinal ganglion cell survival after optic nerve transection, presumably by secreting neurotrophic factors. In addition, the data also demonstrate that Schwann cells could promote intraretinal axonal sprouting. Our findings demonstrate a remarkable glial source of neurotrophic factors with potential clinical applications, as autologous Schwann cells and fibroblasts can be feasibly obtained from peripheral nerves.
