Cell therapy is an attractive therapeutic option in the chronic stage of stroke, where the aim is to recover function through the repair and regeneration of damaged brain tissue. Transplanted cells may directly replace damaged cells or encourage endogenous healing through their effect on neighbouring cells. Various types of neural precursors have been studied, including a human foetal tissue-derived conditionally immortalised cell line that is now in clinical trials. Human embryonic stem cells (hESCs) have potential for therapeutic applications, but neural differentiation protocols have yet to be optimised.
Danielle Drury-Stewart and colleagues at Emory University, USA have previously reported the use of a small molecule based differentiation protocol which reduces the cost and increases efficiency for the in vitro differentiation of neural precursors and neurons. In their recent study published in Stem Cell Research & Therapy they have further characterised the neural precursors derived from hESCs using this protocol, and demonstrated their use in a mouse model of ischaemic stroke.
Neural differentiation of hESCs in vitro was ascertained using immunocytochemistry and electrophysiological recordings. The hESC-derived precursors expressed the neural markers nestin, PAX1 and SOX1. Following re-plating, the cells differentiated into mature neurons and formed well-connected networks expressing the neuronal markers NeuN and neurofilament L. Whole cell patch-clamp recordings showed that the action potentials and potassium currents of the hESC-derived neurons matured over the four week differentiation period.
In vivo, neural precursors were transplanted into the affected area of the mouse brain seven days after induction of a focal ischemic stroke. Cell survival and neuronal differentiation was verified using immunohistochemistry. Transplantation resulted in an increased proportion of BrdU-positive neurons compared to controls, which may be indicative of cell division associated with increased neurogenesis.
In order to determine whether the mice showed signs of functional recovery, the adhesive removal test was administered. Before stroke induction the mice were trained so that they were consistently removing an adhesive dot from both forepaws within 12 seconds. Time to contact and time to completely remove the dot were recorded. The test was repeated four days after stroke to establish a baseline value for impairment and then repeated at one week intervals for up to four weeks after transplantation.
Although there was no significant difference in the outcome measures between the control and transplantation groups as well as no significant change in time to completely remove the dot, the transplant group did show a significant decreasing trend in time to contact that was not seen in the control group.
Collectively, the results suggest that mice who received transplantation show improved sensory function in the stroke-affected forepaw and also a more consistent recovery compared to the control group.
The demonstration that transplantation of hESC-derived neural precursors into the ischemic brain enhances both neurogenesis and sensory function offers further hope for the development of cell therapy for stroke patients.