An imbalance in PFK, a key enzyme in glucose metabolism, might explain why Type 2 diabetics don’t produce enough insulin. When glucose levels rise, PFK is believed to serve as a messenger, directing the pancreas to produce insulin. However, as Prof. Yoram Groner of the Molecular Genetics Department found, an imbalance in PFK composition may garble this directive.
PFK consists of three different sub-units. Working with Ph.D. student Yael Weiss and Dr. Hilla Knobler of Rehovot’s Kaplan Hospital, Groner found that mice with abnormally high levels of the sub-unit known as PFK-L develop symptoms of Type 2 diabetes. The PFK-L gene is located on human chromosome 21, which may explain why children with Down syndrome - the genetic disorder characterized by an extra copy of chromosome 21 - are about 20 times more likely to develop diabetes than are normal children.
The fact that Down syndrome patients have three rather than two copies of this gene may trigger a PFK imbalance leading to impaired insulin production. These findings suggest that the activity level of PFK is important for controlling insulin secretion.
The good communication goal
In binding to receptors on the cell membrane, insulin triggers an array of events through which the body maintains proper energy levels as well as cell growth and proliferation. In the last few years, several insulin signaling mechanisms have been elucidated and shown to involve the sequential activation of enzymes known as protein kinase cascades. Each kinase cascade can be compared to an individual communication line within cells.
Signals are transmitted through the transfer of a phosphate group from one kinase to the next in a specific order, eventually activating an enzyme that initiates a given cellular process. In many of these kinase cascades, the transmission of signals is initiated by insulin; together, these cascades govern all insulin-dependent cellular processes. However, all the communication lines activated by insulin have not as yet been elucidated, including those that participate in regulating the rates of protein synthesis and blood glucose levels.
Prof. Rony Seger of the Biological Regulation Department is working to identify the array of insulin-activated protein kinases. His preliminary results indicate that the stimulation of cells with insulin activates some well-known, as well as some previously unknown, communication lines. Seger is also studying the way in which signals are transmitted from the kinase cascades within the cell to the cell nucleus, where they trigger the activity of genes. The goal is to map the complete pathway of insulin signal transmission in the cell - knowledge that may eventually lead to drugs that would overcome malfunctions in the body’s absorption of glucose.
Making transplants easier
Since diabetes is characterized by the increasing destruction of insulin-producing pancreatic beta cells, advanced diabetes may necessitate transplanting beta cells, the pancreatic islets where they are produced, or even the entire pancreas and a kidney. Transplants are risky, however, first requiring potentially lethal drug or radiation treatment to wipe out the patient’s immune system and prevent transplant rejection. Even after such measures, a residual immunity sometimes causes rejection.
Working with bone marrow transplants for terminal leukemia patients, Prof. Yair Reisner of the Immunology Department has found a way to overcome residual immunity even in the case of transplants from unmatched donors. His method removes the main obstacles limiting the use of mismatched transplants - namely, graft failure and an adverse immunological reaction called graft-versus-host disease.
Normally, a donor and recipient are considered compatible when they are matched for all six immunological markers on their chromosomes - three inherited from the mother and three from the father. In Reisner’s method, developed in collaboration with Prof. Massimo Martelli of Italy’s Policlinico Monteluce, the donor and the recipient need to be matched for only three markers. Such a partial match is always found between parents and children, and there is a 75 percent chance of finding it between siblings.
To date, hundreds of patients throughout Europe have been treated using this approach, yielding significant success rates, as reported in the New England Journal of Medicine, Blood, and other publications. Following these encouraging results, Phase 1 clinical trials are currently under way in major centers in the United States, and the European Bone Marrow Transplantation Society has recently launched a formal prospective study in 35 centers throughout Europe.
A key element of this method is the use of extremely large doses of donor marrow that literally overwhelm the recipient’s rejection mechanism. The donated stem cells are “cleansed” to erase the characteristics contributing to rejection in mismatched transplants. But why does it work? How does bombarding the patient with a megadose of donor stem cells prevent transplant rejection?
A new study by Reisner and his team at the Weizmann Institute’s Department of Immunology provides insights into this riddle. They have shown that certain stem cells, using a “veto” mechanism, are capable of protecting themselves against attack by the body’s immune system. In addition to offering a possible explanation of how stem cells aid in preventing immune rejection, this finding may prove vital in targeting another longstanding research challenge - to lower the radiation dosages accompanying transplant therapies in a range of diseases, from advanced diabetes to leukaemia.
Maintaining blood Vessel integrity
Diabetes-related complications - including blindness, stroke, kidney disease and even gangrene - are largely due to vascular defects. Research by Institute scientists aimed at studying the adhesion and motility of cells in blood vessels may help control these debilitating complications.
The normal function of blood vessels greatly depends on the dynamic properties of the endothelial cells that line the vessel. These cells are firmly attached to the underlying membrane as well as to their neighbors via specialized adhesions, which play a crucial role in regulating vessel formation (angiogenesis), stability and repair. When given a message by angiogenic factors, or following a pathological loss of cell-cell adhesion, endothelial cells extend flattened protrusions with motile properties, form new adhesions and migrate. This physiological response is essential for blood vessel maintenance.
This process can be simulated in the laboratory by an in vitro wound model, where cultured endothelial cells are allowed to migrate into and close a gap that has been artificially introduced into the endothelial layer. Under pathological conditions such as diabetes, the normal maintenance of blood vessels is severely disrupted, leading to increased fragility and malfunction of the vascular system.
Prof. Benjamin Geiger of the Molecular Cell Biology Department is investigating the mechanisms regulating endothelial adhesion and motility. Current studies in his laboratory address the mechanisms underlying these dynamic processes, in healthy and diseased vessels. A better understanding of the molecular mechanisms underlying the generation of new blood vessels and wound closure may point toward possible targets for drug development.
In related research, the work of Prof. Michal Neeman of the Biological Regulation Department may help address the necrotic wounds in the extremities, characteristic of diabetes. Neeman is working on the use of quantitative magnetic resonance imaging (MRI) methods for the analysis of vascular growth in limbs deprived of blood supply. Her objective is to generate criteria for testing the efficacy of therapeutic approaches for blood vessel growth.
Maternal diabetes and the fetal brain
Maternal diabetes is associated with an increased rate of spontaneous abortions, chromosomal aberrations and congenital anomalies in both humans and laboratory animals. Little information is available, however, regarding its impact on the fetal brain.
Using Carbon 13 stable isotopes and magnetic resonance spectroscopy Prof. Aviva Lapidot and her team in the Institute’s Organic Chemistry Department have conducted pioneering studies showing how diabetes can affect the brain.
In particular, they were the first to demonstrate that diabetes in the pregnant mother has adverse effects on the brain of her fetus. It reduces glucose utilization and increases the uptake of other energy “fuels” known as ketone bodies, which are toxic to the fetus. Made of fatty acid degradation products formed in the liver of the diabetic mother, the ketone bodies are transported first from the maternal to the fetal circulation and then to the fetal brain, via the blood-brain barrier. Lapidot’s research aims to clarify the origins of this toxicity and eventually help protect the fetus against it.
Tight glycemic control during diabetic pregnancy has been shown to significantly reduce the occurrence of congenital malformations and other effects of maternal diabetes on the offspring. However, intensive insulin therapy often causes recurrent acute maternal hypoglycemia, which is harmful to the developing fetus.
Lapidot’s team is currently examining the implications of poorly controlled, versus carefully controlled, maternal diabetes on both maternal and fetal brain glucose metabolism, including the potential for neonatal neurological complications.