User:Immcarle73/sandbox

Article Evaluation
-The introduction needs to be longer. Right now, it is only one sentence.

-The function section is decent, but there is limited information. Generally, more research needs to be done on MARCO.

-It may go slightly off topic when describing IMPs, but these might be relevant.

-The article seems neutral.

-The reference links work. They seem to be mostly scholarly articles.

-There are not any conversations in the talk page. It is a Stub-Class article and has been rated as Low-importance.

-The subject brings up topics we have covered in class, but mainly just names terms and does not describe them.

I will also add new headings. Right now there is only a 'Function' heading, but I think there should also be an 'Evolution' or 'Discovery' heading and also 'Associated Diseases', 'Structure', and/or 'Regulation' headings.

-I also just deleted everything within the 'Function' heading that I did not add because it was either word-for-word the same as the source or it was poorly paraphrased so I took it down due to plagiarism. However, most of my sources found the same information, so I plan on re-writing the section so that it has the same content without plagiarism.

-I am considering adding an image of the structure (mainly showing the different domains) of MARCO so that this receptor may be more easily visualized

Potential References
I plan on adding new background information on MARCO such as how it evolved, its specific function, and diseases related to this receptor. I will likely add a couple new Headings and make the introduction a little longer.

A review of macrophage scavenger receptors.

A review of why implants fail sometimes.

This review looks at how scavenger receptors could be used in therapies for Alzheimer's Disease.

This review looks at the antibody IgG, but there is also some discussion of receptors on macrophages such as MARCO.

This is a review of the evolution and function of scavenger receptors including MARCO.

MARCO Draft
MARCO is a class A scavenger receptor that is found on particular subsets of macrophages. Scavenger receptors are pattern recognition receptors (PRRs) and are most commonly found on immune cells. Their defining feature is that they bind to polyanions and modified forms of a type of cholesterol called low-density lipoprotein (LDL). MARCO is able to bind and phagocytose these ligands and pathogen-associated molecular patterns (PAMPs), leading to the clearance of pathogens as well as causing downstream effects in the cell that lead to inflammation. As part of the innate immune system, MARCO clears, or scavenges, pathogens and leads to inflammatory responses. The scavenger receptor cysteine-rich (SRCR) domain at the end of the extracellular side of MARCO is responsible for ligand binding and the subsequent immune responses. Increased MARCO expression on macrophages is also associated with diseases such as prostate and liver cancer, and Alzheimer's disease is associated with decreased response within the cell when a ligand binds to MARCO.

Cell Expression
Certain subtypes of macrophages are likely to express MARCO, but the receptor is also present on circulating monocytes, dendritic cells, and B cells. MARCO is typically present on the macrophages in the marginal zone of the spleen and the medullary lymph nodes, but it is also found in the liver. Dendritic cells increase expression of MARCO when exposed to certain pathogens, which leads to an increase in phagocytosis by the dendritic cell. When ligand binds to MARCO on dendritic cells, the cytoskeleton of the cell is altered, allowing for the formation of the long arms that also increase the phagocytic ability of dendritic cells. Macrophages that constitutively express MARCO are within the spleen marginal zone and medullary lymph nodes. Certain interactions between the macrophage and bacteria up-regulate its expression, as well as stimulating the expression of MARCO on tissue macrophages.

Phagocytosis
The primary function of scavenger receptors is to phagocytose pathogens, but they are also able to participate in cell-cell recognition and are important in initiating inflammatory responses. MARCO, being a PRR, is able to bind to a wide variety of bacteria, making it an important receptor for immunity against bacteria. Both soluble LPS and entire bacteria are able to bind to MARCO. MARCO is also able to bind to both acetylated LDL (AcLDL) and oxidized LDL (OxLDL), as well as to B cells in the marginal zone of the spleen and apoptotic cells. Since MARCO is able to recognize and phagocytose pathogens and apoptotic cells, expression of MARCO increases the phagocytic ability of the cell. MARCO operates independently of opsonization.

Inflammation
MARCO does not directly cause an inflammatory response, but it helps other receptors interact with PAMPs, so they may initiate inflammation. One way MARCO does this is by tethering a pathogen to other proteins on the cell that do cause an inflammatory response. These proteins could be other PRRs such as TLR2. These receptors may then lead to the activation of NF-κB which allows for the production and release of pro-inflammatory cytokines. Through phagocytosis, MARCO also brings pathogens into the cell so that there are more pathogens available to intracellular compartments containing receptors such as TLR3, NOD2, and NALP3 that are capable of initiating an inflammatory response.

Structure
MARCO is a transmembrane protein that has five domains. The first domain is within the cell, called the cytoplasmic domain. Moving into the cell membrane is the transmembrane domain, which is followed by the spacer domain located outside of the cell, then the collagenous domain, and finally the SRCR domain. The SRCR domain is necessary for MARCO to bind to ligands. Other members of the class A scavenger receptors tend to have alpha helical coiled coil domains, but MARCO does not.

The C-terminal SRCR domain of MARCO plays a key role in the ability of the receptor to bind and take up ligand, enhance downstream inflammatory responses, and adhere to surfaces. The SRCR domain is where the ligand binds to MARCO. There are two highly conserved arginine amino acids, called the RxR motif, that are crucial for the binding of the ligand.

Associated Diseases
The activity of MARCO on microglia, the macrophages of the brain, is associated with Alzheimer's disease. One primary characteristic of Alzheimer's disease is the presence of numerous senile plaques in the brain that contain amyloid beta peptides (Aβ). Initially, the microglia clear the Aβ which binds to receptors such as MARCO. As the disease progresses, however, their ability to clear Aβ decreases, resulting in Aβ accumulation. This accumulation of Aβ occurs early on in Alzheimer's disease, harming the brain as Aβ is neurotoxic. MARCO also interacts with formyl peptide receptor (FPR2) to form a complex that causes the microglia to release pro-inflammatory cytokines which leads to inflammation that results in damage to neurons.

MARCO expression is also associated with hepatocellular carcinoma (HCC). A specific type of liver macrophage, called a Kupffer cell, is the predominant source of macrophage expression in the liver. As HCC progresses, there is a decrease in the expression of MARCO in the tumor compared to the tissue surrounding the tumor. If the disease has metastasized, the MARCO expression declines even further. MARCO expression levels are, therefore, good for determining HCC prognosis since higher expression is associated with a higher survival rate and a less severe stage of cancer. Similarly, the number of cells possessing scavenger receptors in those with prostate cancer decreases as the tumor progresses. This decrease in scavenger receptors is associated with a lower survival rate, larger tumor size, more positive lymph nodes, and a higher clinical stage of the cancer.