Science
At the time Dr. Bloch’s research program was initiated, it appeared that there was a single constitutively-expressed nitric oxide (NO) synthase (NOS) in brain and endothelium. Dr. Bloch and his colleagues cloned a distinct NOS isoform responsible for endothelial nitric oxide production, NOS3, ultimately enabling generation of a mouse deficient in NOS3 (in studies led by Dr. Paul Huang, MGH CVRC). They went on to find that NOS3-deficient mice are more susceptible to hypoxia-induced pulmonary vascular remodeling. Conversely, Dr. Bloch and his colleagues, in collaboration with Drs. Jesse Roberts (MGH CVRC) and Warren Zapol (MGH Anesthesia and Critical Care), observed that enhancing pulmonary nitric oxide levels inhalation of nitric oxide gas attenuated hypoxic pulmonary vasoconstriction and prevented pulmonary vascular remodeling. Moreover, they found that nitric oxide inhalation could prevent pulmonary vascular remodeling even before the development of pulmonary vasoconstriction. Taken together, these studies have important implications for the treatment of children with congenital heart disease, in whom pulmonary vascular remodeling often precedes the development of pulmonary hypertension (which is often fatal).
Dr. Bloch and his colleagues, in collaboration with Dr. Marc Semigran (MGH Cardiology Division), showed that nitric oxide inhalation has systemic vascular effects including attenuation of vascular neointima formation after balloon injury and prevention re-thrombosis after coronary artery thrombolysis (the latter is markedly potentiated by inhibitors of cGMP-metabolizing phosphodiesterases). Most recently, in collaboration with Drs. Marielle Scherrer-Crosbie and Michael Picard (both from the MGH Cardiology Division) and Dr. Stefan Janssens (University of Leuven, Belgium), Dr. Bloch and his colleagues observed that breathing nitric oxide decreases myocardial infarction size in mice and pigs subjected to transient coronary artery occlusion. In exciting preliminary clinical studies, Drs. Semigran and Bloch and their colleagues demonstrated that breathing nitric oxide improves cardiac index in patients with right ventricular myocardial infarction complicated by cardiogenic shock. These innovative studies have direct clinical implications for the care of patients with acute coronary syndromes and have led to two randomized clinical trials. In the first clinical trial (led by Dr. Semigran), whether or not breathing nitric oxide can improve cardiac function and improve outcome is being tested in patients presenting with cardiogenic shock. In a second clinical trial (led by Dr. Bloch), the ability of nitric oxide inhalation to decrease myocardial infarction size (using contrast-enhanced magnetic resonance imaging) is being examined in patients undergoing percutaneous coronary intervention for acute ST segment elevation myocardial infarction.
Research in Dr. Bloch’s laboratory has brought into focus the fact that regulation of nitric oxide responsiveness may be as important as regulation of nitric oxide production. They found that prolonged exposure of vascular smooth muscle cells (VSMC) to nitric oxide or pro-inflammatory cytokines decreases function of soluble guanylate cyclase (sGC; the enzyme responsible for cGMP synthesis in response to nitric oxide), desensitizing the cells to nitric oxide. In addition, they observed that cGMP-dependent protein kinase, an enzyme responsible for vasodilation, also has a critical role in determining the sensitivity of these cells to the antiproliferative and proapoptotic effects of nitric oxide and cGMP.
Dr. Bloch’s research group, in collaboration with Drs. Janssens, Picard, and Scherrer-Crosbie, has elucidated an important modulatory role for nitric oxide synthesized by NOS3 in the left ventricular remodeling induced by a variety of hemodynamic challenges. In addition, Dr, Bloch’s group has collaborated with Drs. Fumito Ichinose (MGH Department of Anesthesia and Critical Care) and Warren Zapol to explore the mechanisms responsible for the impairment of hypoxic pulmonary vasoconstriction associated with endotoxemia and volutrauma.
In collaboration with Donald Bloch in the MGH Center for Immunology and Inflammatory Diseases, my research group has used autoimmune sera from patients with primary cirrhosis to characterize the structure and function of two important cellular structures--the nuclear body and the cytoplasmic mRNA processing body. The nuclear body is a nuclear structure that appears to have a critical role in oncogenesis, gene transcription, and the cellular response to viral infection. We have cloned two new nuclear body components, both of which appear to be transcription factors and one of which is a co-activator of nuclear hormone receptors. Cytoplasmic mRNA processing bodies are the location in the cell where the 5’ cap of mRNA is removed; the mRNA is then subjected to 5’ to 3’ degradation. Processing bodies are also the location in the cell where mRNA undergoes siRNA-induced post-transcriptional regulation (either inhibition of translation or mRNA degradation). Using autoimmune sera and new techniques in proteomics, we have identified novel components of mRNA processing bodies including Ge-1, a central component of the processing body that interacts with and regulates both decapping proteins DCP1a and DCP2. In addition, we have identified RAP55 a protein that associates with processing bodies in resting cells and translocates to cytoplasmic mRNA stress granules in the setting of oxidation-induced stress. RAP55 returns to processing bodies during the recovery period, possibly escorting irreversibly damaged mRNA to these structures for degradation.
Figure 1. Identification and characterization of novel components of mRNA processing bodies.
Some of the enzymes that are involved in mRNA degradation are concentrated in discrete locations in the cell known as cytoplasmic mRNA processing bodies (P-bodies). P-bodies have important roles in mRNA degradation and have been implicated in RNAi-mediated post-transcriptional gene silencing. Approximately 5% of patients with the autoimmune disease primary biliary cirrhosis (PBC) have autoantibodies directed against P-bodies and we have used PBC sera to identify new components of these structures. DNA encoding potential new P-body components were expressed fused to green fluorescent protein (GFP) was transfected into Hep-2 cells. In panel A, a fusion protein localized to discrete cytoplasmic dots in the cytoplasm of transfected cells. These dots were shown to be P-bodies using serum from a patient with known anti-P-body autoantibodies (red, panel B). Merge of panels A and B is shown in panel C. DAPI staining (blue) in panel C indicates the location of nuclei. White arrows indicate the location of representative P-bodies.
Most recently, Dr. Bloch and his colleagues have begun a new line of research directed at understanding how mutations in the gene encoding bone morphogenetic protein receptor type 2 (BMPR2) cause primary pulmonary hypertension. They observed that mice carrying one copy of a mutant BMPR2 gene have mild pulmonary hypertension associated with abnormalities of pulmonary vascular structure. Because mice that are homozygous for a mutant BMPR2 gene die early in development, they recently developed mice with a conditional mutation in the BMPR2 gene. Using vascular smooth muscle cells from these mice, Dr. Bloch and his colleagues have already observed that disruption of BMPR2 leads to an unanticipated net gain of signaling by some, but not all, BMP ligands via the activation of an activin type II receptor.
Publications
To find out more about Dr. Kenneth Bloch's research, click here to view his publications.
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