الفهرس 
Stem cellsOnly 14 pages are availabe for public view
 |  | from | 124 |  |  |
| | | from | 124 | | |
Abstract
Stem cell biology has attracted tremendous interest recently. It is
hoped that it will play a major role in the treatment of a number of
incurable diseases via transplantation therapy. Several varieties of stem
cells have been isolated and identified in vivo and in vitro. Very broadly
they comprise of two major classes: embryonic/fetal stem cells and adult
stem cells.
Stem cells are important for living organisms. In the 3- to 5-day-old
embryo, the so called blastocyst, stem cells give rise to the multiple
specialized cell types that make up the heart, bone, lung, skin, and other
tissues. In some adult tissues, such as bone marrow, liver, muscle, and
brain, small populations of adult (or somatic) stem cells control
replacement of cells which are lost through age, injury, or disease.
There are three important characteristics that distinguish stem cells
from other cell types. Stem cells are unspecialized but pluripotent (can
differentiate into all three major tissue types) cells, which have the ability
to indefinitely renew themselves.
Scientists put great effort in the understanding, identification, and
characterization of the various differentiation processes stem cells may
undergo. This leads to an increasing knowledge about how an organism
develops from a single cell and how damaged cells are replaced in adult
organisms. This opens doors for scientists to investigate the possibility of
cell-based therapies to treat disease, which is often referred to as
“regenerative” or “reparative” medicine.
Summary
87
Cell therapy, including the disciplines of regenerative medicine,
tissue, and bio-engineering, is dependent on cell and tissue culture
methodologies to generate and expand specific cells in order to replace
important differentiated functions lost or altered in various disease states.
Therapies aiming to promote renal regeneration need first to
discriminate between the disease states of acute kidney injury (AKI) and
chronic kidney disease (CKD). AKI is a common disease with disparate
etiologies that involve reduced total or partial renal blood flow with
resultant ischemic injury. An ischemic/reperfusion model has therefore
been commonly used as an experimental model of AKI.
(CKD) characterized by a progressive course with ongoing loss of
kidney function. Once (GFR) falls below about half of normal, kidney
function tends to decline even if the initial insult to the kidney has been
eliminated.
End-stage kidney disease (ESKD), defined as the need for dialysis,
receipt of a transplant, or death from chronic kidney failure, generally
affects less than 1% of the population. However ESKD is the end result
(CKD), a widely prevalent but often silent condition with elevated risks
of cardiovascular morbidity and mortality and a range of metabolic
complications. A recently devised classification of CKD has facilitated
prevalence estimates that reveal an “iceberg” of CKD in the community,
of which dialysis and transplant patients are the tip.
In the kidney, tubules and glomeruli show a totally different
plasticity. It is widely known from the clinical practice that, in most
cases, tubules are able to regenerate even after major damage, although
Summary
88
postnatal glomerulogenesis has not been described in human. Probably
for this reason, major acute or chronic glomerular damage invariably
leads to ESRD. The recent identification of renal progenitor cells both
inside the kidney and in the bone marrow may pave the way toward the
future regeneration of the damaged kidney.
Recent progress in stem cell biology has demonstrated that renal stem
cells, with the capability to differentiate into mature renal cells, do exist
in adult individual; however, the debate is ongoing regarding their major
location. Suggestions include the interstitium of the cortex,and papilla,
tubules and bone marrow.
We need to be innovative in our therapy for AKI, CKD and provide a
substitute for dialysis as soon as possible. Regenerative medicine is the
great hope for realizing this goal. Here, we have listed the minimum
requirements for artificial kidney formation de novo and reviewed step by
step the challenges in satisfying them.