New step towards HIV cure

German haematologist Gero Hütteof the Charité Universitätsmedizin in Berlin proposed and experimented a new treatment which may have cured the patient duly from Leukemia and HIV. The procedure was performed two years ago and there is still no relapse of the virus and the dosage of antiretroviral drugs has been stopped. The patient in consideration had stopped responding to chemotherapy and so a transplant was of utmost importance. Dr Hütter took this transplant to the next level by transplanting bone marrow stem cells from a donor with mutation in CCR5 gene. A 32 base pair (bp) deletion mutation within the coding region of the CCR5 gene has been associated with resistance to HIV-1 infection. This gene is responsible for encoding the receptor used by the HIV virus to enter cells. A short mutation in this gene is present in about 1% of European population and people with such mutation are less likely to contract this disease.

Skeptics however do not completely believe in this procedure theorizing that, this was one successfully attempt of the many experiments being conducted on similar lines. Some believe that virus might relapse and may be dormant in some cells like brain or heart which are not feasible to test. Also there is another strain which does not use the CCR5 medium of entry. Also this mutation is present in only 1% of European population and is very rarely observed in African population where the disease is rampant. There have been very less studies pertaining to Asian populations.

Pharmaceutical approaches have also been suggested and there is a drug in existence developed by Pfizer called maraviroc which targets CCR5, preventing binding however the HIV virus still finds a way around this competitive binding. Gene therapy has also been implemented by trying to remove the gene itself and Phase I trials have been launched by Sangamo BioSciences.

Though the technique has many disadvantages it is still a huge step towards curing of HIV.

Reference (http://www.nature.com/news/2009/090211/full/news.2009.93.html)

Image(http://s.wsj.net/public/resources/images/NA-AT825_CURE_NS_20081106180821.gif)

Myocardial Regeneration

(Chapter 1)

Understanding the basics:

In the past decade several attempts have been made to characterize and identify cells capable of differentiating into other lineages different form its organ of origin. Embryonic Stem cells (ESCs) and Bone marrow derived cells (BMCs) were extensively studied and striking advances have been made in utilizing the BMCs regenerative capacity for treating ischemic and nonischemic heart failures. However a lot of controversy surrounds the differentiative capacity of BMCs into cardiac lineages. The presence of a different stem cell compartment in the heart for regeneration of myocardial tissue after infarction has received recognition. Hematopoietic Stem cells (HSCs) with their transdifferentiation capabilities have been identified as the novel form of cell based therapy for regenerating damaged organs. Complete structural and functional recovery of the damaged organ is one of the basic aims of regenerative medicine. Scar formation during recovery from injury is vital for prevent a cascade of uncontrolled lethal events however the scar is biochemically and functionally dissimilar to the original tissue thereby hindering the performance of the organ in question.

Tissue repair in embryos is rapid and virtually scar free. Presence of hyaluronic acid and fibronectin in amniotic fluid has been linked to the interference in scar formation. Moreover less number of inflammatory cells accumulate at the site of Injury (attenuated response) and presence of growth factors such as transforming growth factor-β (TGF-β) isoforms which are not present in adults are deemed responsible for this. There have been studies where adult wounds in rats and mice when exposed to similar profile of cytokines which are present in embryo exhibit more efficient repair with reduction in scar formation.

Exogenous progenitor cells and myocardial repair:

During embryonic and post natal development there is increase in cardiac mass which reflects the delicate balance between formation of new myocytes and deletition of unwanted cells. Growth in myocyte right from birth is responsible for the adult heart phenotype. Cell homeostasis and optimal pump performance are often maintained by intrinsic growth factors however increased pressure or stress results in myocyte hypertrophy, apoptosis and necrosis which constitutes as infarction. Ischemic injury often results in decrease in number of myocytes and scarring. Numbers of experiments aimed at replacement of dead tissue with feasible cells have been developed to overcome this obstacle. Different types of cells were employed for experimentation of myocardial regeneration, these include skeletal myoblasts, embryonic myoblasts right upto bone marrow c-kit positive and negative progenitor cells. Mostly the implanted cells formed a passive graft and successfully decreased the stiffness around the scarred area and enhanced cardiac function. The possibility of a paracrine effect on resident cardiac stem cells by the implanted cells activating myocardial regeneration has been postulated however there has been little success in identification of the most appropriate form of cell therapy for myocardial repair.

Reference (Leri, A. et.al., Cardiac Stem Cells and Mechanisms of Myocardial Regeneration)

Pure Information (Senescence)

Senescence (Aging)

Hayflick’s Limit:

In 1961 Leonard Hayflick and Paul Moorhead discovered that human cells derived from embryonic tissues can only divide a finite number of times in culture. They divided the cells into 3 phases.

Phase 1: Primary culture, cells grow until they cover the flask.

Phase 2: Cells from Phase 1 have no space for expansion hence are subcultivated i.e. cell suspension divided into two new flasks

Phase 3: Slow dividing cells mark this phase. Cells may or may not die

Cumulative population doublings (CPDs) is the term reserved for expansion of cells and cultures stopped dividing after an average of fifty CPD’s. This phenomenon is known as Hayflick's limit, Phase III phenomenon, or, replicative senescence (RS). There has been a direct relation between the number of CPDs and the species from which the cells were derived.

Some divide 110 times (cells from the Galapagos tortoise) while some only 15 (mouse). Immortal cell lines like embryonic stem cells, stem cells from tumors evade RS.

Biomarkers of RS:

Cell Growth: - The most obvious marker is cell growth. Cells do not continue to divide even vigorously dividing cells reach quiescence during G1 to S phase of the cell growth cycle. External stimulants like growth factors are incapable of stimulating the expansion of senescent cells although senescent cells remain metabolically active.

Cell Morphology: - Senescent cells are bigger and have more diverse morphologies, so also cell density in the confluent culture is less as they are more sensitive to cell-cell inhibition.

Other factors: Enzymes like β-galactosidase has been associated with senescence. Each subcultivation also introduces polyploidy in cells and also mitochondrial DNA undergoes mutations leading to senescence. Cardiac senescence is associated with enhanced expression of Angiotensin Type II receptor subtypes. Senescent cells have also less ability to express heat shock proteins, (the upregulation of heat shock proteins is carried out by heat shock factors). There is upregulation of several genes in vitro cellular senescence. There is also increase in metalloproteinases, which degrade the extracellular matrix.

Stress Induced Senesce:

In normal conditions in human cells O₂ has been exhibited to accelerate growth arrest. Cytotoxic conditions (more than 50% O₂) have been associated with premature cellular senescence. the term stress-induced premature senescence (SIPS) was coined in 1999, at the EMBO workshop of Molecular and Cellular Gerontology, Olivone, Switzerland (Brack et al., 2000).

Reference (http://www.senescence.info/cells.html)