Abstract
Stroke may cause severe death and disability but many clinical trials have failed in the past, partially because the lack of an effective method to regenerate new neurons after stroke. In this study, we report an in vivo neural regeneration approach through AAV NeuroD1-based gene therapy to repair damaged brains after ischemic stroke in adult non-human primates (NHPs). We demonstrate that ectopic expression of a neural transcription factor NeuroD1 in the reactive astrocytes after monkey cortical stroke can convert 90% of the infected astrocytes into neurons. Interestingly, astrocytes are not depleted in the NeuroD1-converted areas, consistent with the proliferative capability of astrocytes. Following ischemic stroke in monkey cortex, the NeuroD1-mediated astrocyte-to-neuron (AtN) conversion significantly increased local neuronal density, reduced microglia and macrophage, and surprisingly protected parvalbumin interneurons in the converted areas. Furthermore, the NeuroD1 gene therapy showed a broad time window in AtN conversion, from 10 to 30 days following ischemic stroke. The cortical astrocyte-converted neurons showed Tbr1+ cortical neuron identity, similar to our earlier findings in rodent animal models. Unexpectedly, NeuroD1 expression in converted neurons showed a significant decrease after 6 months of viral infection, indicating a downregulation of NeuroD1 after neuronal maturation in adult NHPs. These results suggest that in vivo cell conversion through NeuroD1-based gene therapy may be an effective approach to regenerate new neurons for tissue repair in adult primate brains.
Highlights
Stroke is an important cause of long-term disability with a high mortality rate (Ovbiagele et al, 2013; Benjamin et al, 2018)
Because mouse brains are far different from human brains, it is uncertain whether such in vivo cell conversion technology would be applicable for future human clinical trials
The middle cerebral artery occlusion (MCAO) model is widely used in rodent animals, previous studies in non-human primates (NHPs) reported high mortality rate of MCAO model and large variations in the infarct size (Cook and Tymianski, 2012)
Summary
Stroke is an important cause of long-term disability with a high mortality rate (Ovbiagele et al, 2013; Benjamin et al, 2018). Our group previously reported that in vivo overexpression of a single neural transcription factor NeuroD1 can convert endogenous glial cells directly into functional neurons (Guo et al, 2014), providing a new approach for neural repair in the brain and spinal cord. Many experimental parameters obtained from rodent animal models cannot be extrapolated to human patients, evidenced by many failed stroke clinical trials over the past decades (O’Collins et al, 2006; Diener et al, 2008; Turner et al, 2013; Percie du Sert et al, 2017) This might be due to significant difference between rodents and primates in terms of brain volume, white matter content, complexity of brain structures, and genetic compositions. Large animal species may be more valuable animal models than rodents to evaluate the effectiveness of stroke therapy as they seem to closely mimic the human brain anatomy (Boltze et al, 2017; Modo et al, 2018)
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