CDNA Microarray Screening Of The Differentially Expressed Transcripts And Upregulation Of SPARC In The Deafferented Hippocampus

To elucidate the molecular mechanisms underlying the plasticity events in thecentral nervous system after injury, we analyzed the gene expression profiles in the rathippocampus 10 days following transactions of the entorhinal afferents by usingcDNA microarray technique. Of 6234 genes and expressed sequence tags (ESTs)spotted, 152 exhibited differential expression by ≥ 1.5 fold in the denervatedhippocampus from the control, with 120 down-regulated and 32 up-regulated. Weconfirmed the increase of expression of eight transcripts encoding protein SPARC,thymosin-b4, gelsolin, MHC I, MHC II, b2-microglobulin, and interferon-γ receptorusing Northern bloting. In situ hybridization revealed that the up-regulation of allthese 8 transcripts localized specifically in the denervated target areas, thehippocampal stratum lacunosum-moleculare, and the dentate outer molecular layer.The results suggest that these molecules may have roles in the plasticity events in thehippocampus after entorhinal deafferentation.SPARC is a matricellular protein that modulates cell–cell and cell–matrixinteractions by virtue of its antiproliferative and counteradhesive properties. Thisstudy report the denervation-induced upregulation of SPARC mRNA and protein inthe mouse hippocampus following transections of the entorhinal afferents. Northernblot analysis showed that SPARC mRNA was upregulated in a transient manner in thedeafferented mouse hippocampus. In situ hybridization and immunohistochemistryconfirmed the temporal upregulation of both SPARC mRNA and protein specificallyin the denervated areas, which initiated at 7 days postlesion, reached the maximum at15 as well as 30 days postlesion, and subsided towards normal levels by 60 dayspostlesion. Double labeling by a combination of in situ hybridization for SPARCmRNA with immunohistochemistry for glial fibrillary acidic protein and doubleimmunofluorescence staining for both proteins in the hippocampus revealed thatSPARC-expressing cells are reactive astrocytes. In respect to the spatiotemporalalterations of SPARC expression in the denervated hippocampus, we suggest thatSPARC may be involved in modulation of the denervation-induced plasticityprocesses such as glial cell proliferation, axonal sprouting and subsequentsynaptogenesis in the hippocampus following entorhinal deafferentation.