Most of the ideas here are based mostly on this paper: Phagocytic Clearance in Neurodegeneration and the Wikipedia article on microglia. Shinjini is not done reading the said article yet (as of 6/10/14). She will also look into some others the are mentioned at the end.
Why work on macrophages vs neurons:
- Problem of getting circuit into neurons. Macrophages apparently evolve into microglia once in the cell, as mentioned in a paper (paper: Phagocytic Clearance in Neurodegeneration), so would solve the problem of getting the circuit in the brain. (Needs more research.)
- Macrophages are easy to culture, so experiments on it would be more accurate as opposed to mimicking neurons in vitro.
- Macrophages move about, so would have better chances of finding the AB oligomers.
- It would address the destroying plaques already formed problem (paper: Phagocytic Clearance in Neurodegeneration).
- Faulty phagocytosis in microglia are already indicated as potential problem, which is something to look into (paper). Apparently, the problem is microglia being activated for too long, releasing molecules essential for their function, which are also toxic for the neurons. Ideally, our circuit should be able to detect AB before the plaques are formed, avoiding microglia activation.
How the circuit needs to be adjusted for this:
- Macrophages will not be able to reduce the amount of BACE1 already being produced by neurons, which might be a problem. But if a lower ratio of BACE1/BACE2 already works or if higher levels of BACE2 naturally causes BACE1 levels to drop, would solve the problem. However, microglia are indicated to be contributors to the formation of AB, too, so this might still work. Needs research. (paper)
Other things to look into:
- Microglia already have AB receptors. Maybe we should look into that. (paper: Phagocytic Clearance in Neurodegeneration)
- Does the fact that microglia take up soluble AB affect us in any way? (Brian's paper, 6/10, Microglia take up soluble AB by macropinocytosis)
One paper (paper: Anti-Aß immunotherapy in Alzheimer's disease; relevance of transgenic mouse studies to clinical trials Anti-Aß immunotherapy in Alzheimer's disease; relevance of.pdf) is showing that infiltration by T-cells ( CD4+ and CD8+) is really bad (associated with meningoencephalitis). Shinjini wonders if infiltration by macrophages has a similar detrimental effect (but she has not found strong evidence to support this, other than that microglia activation is indicated as contributing to AD. Need to look into that.)
Papers Shinjini is looking into (as of 6/10/14):
Phagocytic Clearance in Neurodegeneration (Phagocytic clearance in Neurodegeneration (and AD).pdf)
Variant of TREM2 Associated with the Risk of Alzheimer’s Disease (TREM2 variant and WBC as AD risk factor.pdf)
N-APP binds DR6 to cause axon pruning and neuron death via distinct caspases (DR6 death receptor and N-APP (beta-amyloid cousin) binding.pdf)
6/11/14
Further reading of "Phagocytic Clearance in Neurodegeneration" revealed that AB (which form?) causes an inflammatory response in microglia that is responsible for neurodegeneration, while upregulating anti-inflammatory cytokines could help increase phagocytic activity and reduce neurodegeneration. Could that be an added/alternate approach? How would we test if it is working?
Looking into:
Also need to look into:
Do macrophages actually "evolve" into microglia once in the brain or are they different?
6/12/14
Anti-inflammatory cytokines involved in a LOT of other things apparently. May not be the best approach to mess with them.
Brian was excited about macrophages/microglia as chassis idea. Relevant paper: Microglia in the adult brain arise from Ly-6ChiCCR2+ monocytes only under defined host conditions
6/23/14
The papers think EP2 could be a potential target for AD treatment.
EP2 potential target for AD. Knocking out EP2 increases phagocytosis of AB-immunoreactive material (hence, AB) by a LOT, and microglia lacking EP2 do not cause neurodegeneration. EP2 has been associated with other brain disorders. Detrimental effects of EP2-/-: Salt−sensitive hypertension and reduced fertility in mice lacking the prostaglandin EP
2 receptor,
Neuroprotective Function of the PGE2EP2 Receptor in Cerebral Ischemia.
We could downregulate EP2 in microglia in response to AB (same as we are planning for BACE1 currently). Since they will only be in microglia, the shouldn't cause problems with other cells. The system should shut down without AB signalling.
6/26/14
I found this paper from Nature (Targeting gene-modified hematopoietic cells to the centralnervous system: Use of green fluorescent protein uncovers microglial engraftment) which showed:
mice which had undergone a bone marrow transplant with GFP-expressing bone marrow cells had GFP-expressing microglia in their brains at a substantial level after four months, which means there is a circulating microglial precursor in our blood (Ly6Chi CCR2+, according to another paper). Engraftment increased and was directed to specific areas of the brain if their was some sort of damage to that area of the brain.
Basically, this would solve our delivery problems. However, this paper is from 2001. They used a full body irradiation of their test mice. And according to this paper, published 2007 in Nature (Microglia in the adult brain arise from Ly-6Chi CCR2+ monocytes only under defined host conditions), the recruitment does not happen if the mice's heads are not irradiated. So, the fact that the first paper irradiated the whole body of the mice may negate their results.
Other interesting things, though (from first paper):
IMPORTANT: "The decreased propensity of the MSCV promoter to transcriptional silencing in vivo is of particular relevance in the CNS where gene silencing is pertinent." *red-flag, red-flag!*
Not so important: "Recently, cells derived from bone marrow (BM) were found to enter the brain in adult life to differentiate into microglia, astrocytes and neurons2–4"