Matt Gethers/20.380 HIV Project/Meeting Notes/3.18.09 Refine RBC Idea
3.18.09 Meeting: Refine RBC Idea
- Discuss questions everyone was assigned a few weeks ago.
- What do we want out of John and Darrel tomorrow?
- What do we need to put into the person? What stage of progenitor cells? - (done!)
- Immunity issues with progenitor cells? - Rob
- How to couple CD4 expression, etc with RBC differentiation? - Rob
- What to do with HIV once in cell? Do we need it to do anything? - Rob
- How are RBCs removed/recycled from body? - Courtney
- Malaria - Courtney
Can HIV infect progenitor cells?
"Patients with HIV-1 often present with a wide range of hematopoietic abnormalities, some of which may be due to the presence of opportunistic infections and to therapeutic drug treatments. However, many of these abnormalities are directly related to HIV-1 replication in the bone marrow (BM). Although the most primitive hematopoietic progenitor cells (HPCs) are resistant to HIV-1 infection, once these cells begin to differentiate and become committed HPCs they become increasingly susceptible to HIV-1 infection and permissive to viral gene expression and infectious virus production." (Alexaki) Note: there's a figure (1) in this paper that details which cells are susceptible to HIV infection.
- Error fetching PMID 19112504:
What's necessary and sufficient for HIV infection?
"The notion that a coreceptor is required for HIV-1 entry stemmed from the awareness that CD4 expression is not sufficient to explain HIV-1 tropism for different target cells in vitro (see 4 for review and citations). Two related phenomena led to this conclusion. The first series of findings, initially reported in the mid-1980s and extended through the early 1990s, was based on curious results with recombinant human CD4. The receptor was found to render cells permissive for Env-mediated fusion/entry/infection, but only when expressed on a human cell type. Experiments with cell hybrids supported the conclusion that this restriction was due to the requirement for a cofactor (coreceptor) of unknown identity that is specific to human cells, rather than to the presence of a fusion inhibitor on the nonhuman cells." (Berger)
"Because of its new-found activity in HIV-1 Env-mediated fusion, the protein was named “fusin” (6). Its role as a coreceptor was based on both gain-of-function experiments demonstrating that coexpression of fusin along with CD4 rendered nonhuman cells permissive for Env-mediated cell fusion and infection, and loss-of-function experiments showing that anti-fusin antibodies potently inhibited fusion and infection of primary human CD4+ T lymphocytes. Most importantly, both types of analyses indicated that fusin functioned for TCL-tropic, but not M-tropic, HIV-1 strains. Fusin thus fit the criteria for the TCL-tropic HIV-1 coreceptor." (Berger).
- Error fetching PMID 10358771:
Some interesting stuff
- How to prevent HIV from leaving RBC? - Jessie
- Nothing in the literature indicates anything about an "abandon infection" behavior by the HIV.
- Death switch? - Jessie
- Is it necessary? RBCs have a life span of 120 days, and they can't replicate.
- Most of the "suicide" genes are for chemotherapy drugs, which means the drugs have a relatively high degree of toxicity, or for anti-viral therapies.
- Example: HSV-1-TK gene with gancyclovir
- Error fetching PMID 8390693:
- RBCs also lack a lot of cellular machinery. How would suicide gene work?
- Exploding RBCs? - David
- Any natural conditions where RBCs die or explode? - David
- A normal erythrocyte has a volume of about 90 fL=9.0 X 10^-17 L (a third of which is hemoglobin only freed up if we knock it out)
- HIV is roughly a sphere of diameter 120nm --> volume of 9.05 X 10^-22 L
- A normal RBC can theoretically hold a maximum of ~100,000 HIV virions if it has nothing else inside, including water
- Damaged/misshapen RBCs are naturally destroyed in the spleen (i.e. anything but biconcave cells)
- There is an entire class of disorders classified as "Hemolytic anemia" where RBCs are broken down prematurely/too much (http://en.wikipedia.org/wiki/Haemolytic_anemia)
- Some are congenital
- misshapen membrane
- metabolic defects
- sickle-cell anemia
- Some are acquired
- autoimmune disorders
- some drugs (ribavirin)
- malaria and some other infections
- How many copies of HIV do we expect each RBC to hold? (question for modeling)
- Can't find any papers on what happens when HIV virions aggregate in a small volume (could anything bad/unexpected happen? cross-linking?)
- If we knock out hemoglobin, do we need to worry about too little osmotic pressure inside? Is Hb just replaced by ions from blood?
- Take out hemoglobin? Anything else to knock out? - Yi
- Erythrocytes also play a part in the body's immune response: when lysed by pathogens such as bacteria, their hemoglobin releases free radicals that break down the pathogen's cell wall and membrane, killing it
- RBC shear stress in constricted vessels, they release ATP which causes the vessel walls to relax and dilate
- When deoxygenated, erythrocytes release S-nitrosothiols which also acts to dilate vessels
- Structure: no DNA/RNA/mitochondria/insulin receptor. Use glycolysis. No repair.
- 2million/sec from bone marrow, mature: 7 days, live: 100-120 days
- Fe & biliverdin (bilirubin + jaundice)
- hemoglobin important in keeping shape of red blood cells
- Pathologies of RBCs - esp. sickle cell anemia, thalassemia - Yi
- Sickle cell: deoxygenated = misshape
- Thalassemia: abnormal ratio of alpha vs. beta units
- Spherocytosis: cytoskeleton defect; RBC small, sphere-shaped, fragile, prone to hemolysis
- Pernicious anemia (autoimmune): body can’t absorb vitamin b12 – needed to produce hemoglobin
- aplastic anemia: bone marrow can’t produce blood cells
- Hemolysis: general break down of RBC; several causes
- Polycythemias/erythrocytoses: too much RBC; increased viscosity
- due to low O2, malignancy, dehydration
- athletes, high elevation, smoker
- symptoms: headache, vertigo, enlarged spleen/liver
- issues: high blood pressure, blood clots
- marker: high hematocrit (analyze blood)
- hematochromatosis: excess iron; accumulate in tissues and organs and disrupt function, e.g. heart failure
- Ideal concentration of RBC progenitors? - Steph
- How to get into bone marrow? Easy injection method? - Steph
- Role of progenitors? - Steph