Significant changes in endogenous retinal gene expression assessed 1 year after a single intraocular injection of AAV-CNTF or AAV-BDNF

Abstract

Use of viral vectors to deliver therapeutic genes to the central nervous system holds promise for the treatment of neurodegenerative diseases and neurotrauma. Adeno-associated viral (AAV) vectors encoding brain-derived neurotrophic factor (BDNF) or ciliary derived neurotrophic factor (CNTF) promote the viability and regeneration of injured adult rat retinal ganglion cells. However, these growth-inducing transgenes are driven by a constitutively active promoter, thus we examined whether long-term AAV-mediated secretion of BDNF or CNTF affected endogenous retinal gene expression. One year after the intravitreal injection of AAV-green fluorescent protein (GFP), bi-cistronic AAV-BDNF-GFP or AAV-CNTF-GFP, mRNA was extracted and analyzed using custom 96 well polymerase chain reaction arrays. Of 93 test genes, 56% showed significantly altered expression in AAV-BDNF-GFP and/or AAV-CNTF-GFP retinas compared with AAV-GFP controls. Of these genes, 73% showed differential expression in AAV-BDNF versus AAV-CNTF injected eyes. To focus on retinal ganglion cell changes, quantitative polymerase chain reaction was undertaken on mRNA (16 genes) obtained from fixed retinal sections in which the ganglion cell layer was enriched. The sign and extent of fold changes in ganglion cell layer gene expression differed markedly from whole retinal samples. Sustained and global alteration in endogenous mRNA expression after gene therapy should be factored into any interpretation of experimental/clinical outcomes, particularly when introducing factors into the central nervous system that require secretion to evoke functionality.

Effects of AAV-mediated knockdown of nNOS and GPx-1 gene expression in rat hippocampus after traumatic brain injury

“…Effects of gene knockdown on downstream cell signaling pathways could have unpredictable changes on the functional outcome measures we employ to assess effects of gene silencing. While we did not detect any effects of the AAV siRNA vectors on hippocampal-dependent behavioral tests, other studies have found a single injection of AAV alters endogenous gene expression a year post-injection [ 76 ]. Thus, our study does not preclude long term genomic changes that may result from acute AAV siRNA-mediated reduction in degenerating neurons in the hippocampus; these changes may preserve other cognitive functions not tested in our study.…”

Cortical AAV-CNTF Gene Therapy Combined with Intraspinal Mesenchymal Precursor Cell Transplantation Promotes Functional and Morphological Outcomes after Spinal Cord Injury in Adult Rats

“…However the resultant long-term upregulation of protein kinases such as mTOR, a key regulator of protein translation in neurons, leads to some aberrant growth [ 48 ] and progressive changes in the growth of cells, their dendrites, and their axons [ 46 ]. This is not dissimilar to the effect of long-term (up to one year) AAV-mediated expression of CNTF on retinal ganglion cells, where there are not only changes in the dendritic morphology of transduced and neighboring nontransduced cells [ 51 ], but there is also altered expression of endogenous retinal genes [ 52 ]. Whether such effects are also seen in cortical neurons transduced with AAV-CNTF is yet to be determined, but this is an important topic for future studies.…”

Genome expression profiling predicts the molecular mechanism of peripheral myelination

“…AKT silencing was previously reported to be associated with hypomyelination ( 38 ). The expression of PLCG2 was revealed to be sensitive to ciliary neurotrophic factor ( 39 ), a cytokine which may promote peripheral nerve regeneration ( 40 ). Consequently, the NK cell mediated cytotoxicity and BCR signaling pathways may be associated with PNS myelination through FCGR, RAC2 and PLCG2.…”