Transmigration of monocytes into the brain in vivo

Alzheimer`s disease is a chronic neurodegenerative disorder characterized by the presence of beta-amyloid plaques, tau pathology, cerebrovascular damage, inflammation and cell death of cholinergic neurons. The lack of acetylcholine in the cortex and hippocampus directly correlates with cognitive decline and memory deficits in this disease. Current efforts to develop better treatments for Alzheimer`s disease aim to protect these cholinergic neurons or replace the neurotransmitter loss of acetylcholine. Thus far, nerve growth factor (NGF) has been shown as one of the most effective molecules against cholinergic loss and neurodegeneration. However, NGF is a large molecule and cannot pass through the blood-brain barrier (BBB). Previous clinical investigations involving NGF delivery have been performed either by directly infusing NGF or by transplanting NGF-secreting cells into the brains of Alzheimer`s disease patients. In our lab we are interested in using monocytes as a vehicle for non- invasive NGF delivery into the brain. Recently, we have shown (Böttger et al., 2010) in proof-of-principle that NGF-secreting monocytes can pass through an in vitro BBB and support the survival of cholinergic neurons in organotypic brain slices. The aim of this present study is to use monocytes as vehicles for NGF and acetylcholine transport in vivo. In addition, we plan to test whether the NGF-loaded vehicles can provide protection for cholinergic neurons against neurodegeneration and whether the acetylcholine-secreting monocytes can provide replacement for acetylcholine in the cortex. In detail, we aim (1) to generate primary monocytes, which produce and secrete high amounts of acetylcholine and nerve growth factor in vitro, (2) to define the pro-inflammatory status of transmigrated monocytes in vivo and to counteract inflammation and (3) to counteract cognitive impairment and decline of cholinergic activity in vivo using transmigration of acetylcholine and NGF-secreting monocytes. We will use two different animal models: (1) a hypercholesterolemia model which we have recently characterized (Ullrich et al., 2010) and (2) a well established Alzheimer mouse model. We will test spatial memory in an 8-arm radial maze, cortical levels of acetycholine and NGF, survival of cholinergic neurons and inflammatory processes in vivo. In summary, we aim to use our monocyte transmigration strategy to counteract cholinergic decline and cognitive impairment in the brain and to better understand the parameters that effect monocyte transmigration. These experiments should demonstrate the novel innovative strategies that monocyte delivery can provide for future Alzheimer`s disease therapies.

Neurodegenerative disorders of the brain play an important role in Parkinsons and Alzheimers disease. Neurons degenerate which express and release the neurotransmitter dopamine (Parkinson) or acetylcholine (Alzheimer). In basic science one aims to counteract the cell death of these neurons. Growth factors are of particular interest and it is known that glial-cell line derived neurotrophic factor and the classical nerve growth factor (NGF) protect neurons in Parkinsons or Alzheimers disease, respectively. However, the major problem is to deliver these large proteins directly into the brain, where the growth factors are needed. In the present project we aimed to use blood cells to deliver NGF directly into the brain. We isolated monocytes from the blood of a mouse and tested possibilities to load these cells with NGF. Then these monocytes were again applied into mice via the tail veins. We used a model, where the blood-brain barrier is disturbed to enhance transmigration, the hypercholesterolemia mouse model and a transgenic Alzheimer mouse. In the first model we could show that NGF loaded monocytes counteracted cell death of acetylcholine producing neurons. In the second model we showed that transmigrated monocytes could eliminate toxic plaques in the brain. Taken together, our work shows that exogenous applied blood cells (monocytes) can cross a disturbed blood-brain barrier and have protective activity in the brain. This may open a chance for therapeutic applications, but the complex isolation and loading of monocytes turns out to be a problem. As an alternative we tested another blood cell, the thrombocytes/platelets, which are easier to isolate.