Long-Term Gene Therapy Causes Transgene-Specific Changes in the Morphology of Regenerating Retinal Ganglion Cells

Recombinant adeno-associated viral (rAAV) vectors can be used to introduce neurotrophic genes into injured CNS neurons, promoting survival and axonal regeneration. Gene therapy holds much promise for the treatment of neurotrauma and neurodegenerative diseases; however, neurotrophic factors are known to alter dendritic architecture, and thus we set out to determine whether such transgenes also change the morphology of transduced neurons. We compared changes in dendritic morphology of regenerating adult rat retinal ganglion cells (RGCs) after long-term transduction with rAAV2 encoding: (i) green fluorescent protein (GFP), or (ii) bi-cistronic vectors encoding GFP and ciliary neurotrophic factor (CNTF), brain-derived neurotrophic factor (BDNF) or growth-associated protein-43 (GAP43). To enhance regeneration, rats received an autologous peripheral nerve graft onto the cut optic nerve of each rAAV2 injected eye. After 5–8 months, RGCs with regenerated axons were retrogradely labeled with fluorogold (FG). Live retinal wholemounts were prepared and GFP positive (transduced) or GFP negative (non-transduced) RGCs injected iontophoretically with 2% lucifer yellow. Dendritic morphology was analyzed using Neurolucida software. Significant changes in dendritic architecture were found, in both transduced and non-transduced populations. Multivariate analysis revealed that transgenic BDNF increased dendritic field area whereas GAP43 increased dendritic complexity. CNTF decreased complexity but only in a subset of RGCs. Sholl analysis showed changes in dendritic branching in rAAV2-BDNF-GFP and rAAV2-CNTF-GFP groups and the proportion of FG positive RGCs with aberrant morphology tripled in these groups compared to controls. RGCs in all transgene groups displayed abnormal stratification. Thus in addition to promoting cell survival and axonal regeneration, vector-mediated expression of neurotrophic factors has measurable, gene-specific effects on the morphology of injured adult neurons. Such changes will likely alter the functional properties of neurons and may need to be considered when designing vector-based protocols for the treatment of neurotrauma and neurodegeneration

Anti-hypertensive agents do not prevent blood-brain barrier dysfunction and cognitive deficits in dietary-induced obese mice

BACKGROUND: While vascular risk factors including Western-styled diet and obesity are reported to induce cognitive decline and increase dementia risk, recent reports consistently suggest that compromised integrity of cerebrovascular blood-brain barrier (BBB) may play an important role in neurodegeneration and cognitive deficits. A number of studies report that elevated blood pressure increases the permeability of BBB. METHODS: In this study, we investigated the effects of anti-hypertensive agents, candesartan or ursodeoxycholic acid (UDCA), on BBB dysfunction and cognitive decline in wild-type mice maintained on high fat and fructose (HFF) diet for 24 weeks. RESULTS: In HFF-fed mice, significantly increased body weight with elevated blood pressure, plasma insulin and glucose compared to mice fed with low-fat control chow was observed. Concomitantly, significant disruption of BBB and cognitive decline were evident in the HFF-fed obese mice. Hypertension was completely prevented by the co-provision of candesartan or UDCA in mice maintained on HFF diet, while only candesartan significantly reduced the body weight compared to HFF-fed mice. Nevertheless, BBB dysfunction and cognitive decline remained unaffected by candesartan or UDCA. CONCLUSIONS: These data conclusively indicate that modulation of blood pressure and/or body weight may not be directly associated with BBB dysfunction and cognitive deficits in Western diet-induced obese mice, and hence anti-hypertensive agents may not be effective in preventing BBB disruption and cognitive decline. The findings may provide important mechanistical insights to obesity-associated cognitive decline and its therapy