Brian R. Wamhoff

Bio: Brian R. Wamhoff is an academic researcher from University of Virginia. The author has contributed to research in topics: Microbubbles & Myocyte. The author has an hindex of 37, co-authored 89 publications receiving 6669 citations. Previous affiliations of Brian R. Wamhoff include University of Missouri.

Molecular Regulation of Vascular Smooth Muscle Cell Differentiation in Development and Disease

Abstract: The focus of this review is to provide an overview of the current state of knowledge of molecular mechanisms/processes that control differentiation of vascular smooth muscle cells (SMC) during normal development and maturation of the vasculature, as well as how these mechanisms/processes are altered in vascular injury or disease. A major challenge in understanding differentiation of the vascular SMC is that this cell can exhibit a wide range of different phenotypes at different stages of development, and even in adult organisms the cell is not terminally differentiated. Indeed, the SMC is capable of major changes in its phenotype in response to changes in local environmental cues including growth factors/inhibitors, mechanical influences, cell-cell and cell-matrix interactions, and various inflammatory mediators. There has been much progress in recent years to identify mechanisms that control expression of the repertoire of genes that are specific or selective for the vascular SMC and required for its differentiated function. One of the most exciting recent discoveries was the identification of the serum response factor (SRF) coactivator gene myocardin that appears to be required for expression of many SMC differentiation marker genes, and for initial differentiation of SMC during development. However, it is critical to recognize that overall control of SMC differentiation/maturation, and regulation of its responses to changing environmental cues, is extremely complex and involves the cooperative interaction of many factors and signaling pathways that are just beginning to be understood. There is also relatively recent evidence that circulating stem cell populations can give rise to smooth muscle-like cells in association with vascular injury and atherosclerotic lesion development, although the exact role and properties of these cells remain to be clearly elucidated. The goal of this review is to summarize the current state of our knowledge in this area and to attempt to identify some of the key unresolved challenges and questions that require further study.

Identification of a Novel Macrophage Phenotype That Develops in Response to Atherogenic Phospholipids via Nrf2

Abstract: Rationale: Macrophages change their phenotype and biological functions depending on the microenvironment. In atherosclerosis, oxidative tissue damage accompanies chronic inflammation; however, macrophage phenotypic changes in response to oxidatively modified molecules are not known. Objective: To examine macrophage phenotypic changes in response to oxidized phospholipids that are present in atherosclerotic lesions. Methods and Results: We show that oxidized phospholipid-treated murine macrophages develop into a novel phenotype (Mox) that is strikingly different from the conventional M1 and M2 macrophage phenotypes. Compared to M1 and M2, Mox macrophages show a different gene expression pattern, as well as decreased phagocytotic and chemotactic capacity. Treatment with oxidized phospholipids induces both M1 and M2 macrophages to switch to the Mox phenotype. Whole-genome expression array analysis and subsequent gene ontology clustering revealed that the Mox phenotype was characterized by abundant overrepresentation of Nrf2-mediated expression of redox-regulatory genes. In macrophages isolated from Nrf2 −/− mice, oxidized phospholipid-induced gene expression and regulation of redox status were compromised. Moreover, we found that Mox macrophages comprise 30% of all macrophages in advanced atherosclerotic lesions of low-density lipoprotein receptor knockout (LDLR −/− ) mice. Conclusions: Together, we identify Nrf2 as a key regulator in the formation of a novel macrophage phenotype (Mox) that develops in response to oxidative tissue damage. The unique biological properties of Mox macrophages suggest this phenotype may play an important role in atherosclerotic lesion development as well as in other settings of chronic inflammation.

Myocardin Is a Key Regulator of CArG-Dependent Transcription of Multiple Smooth Muscle Marker Genes

Abstract: The interactions between serum response factor (SRF) and CArG elements are critical for smooth muscle cell (SMC) marker gene transcription. However, the mechanisms whereby SRF, which is expressed ubiquitously, contributes to SMC-specific transcription are unknown. Myocardin was recently cloned as a coactivator of SRF in the heart, but its role in regulating CArG-dependent expression of SMC differentiation marker genes has not been clearly elucidated. In this study, we examined the expression and the function of myocardin in SMCs. In adult mice, myocardin mRNA was expressed in multiple smooth muscle (SM) tissues including the aorta, bladder, stomach, intestine, and colon, as well as the heart. Myocardin was also expressed in cultured rat aortic SMCs and A404 SMC precursor cells. Of particular interest, expression of myocardin was induced during differentiation of A404 cells, although it was not expressed in parental P19 cells from which A404 cells were derived. Cotransfection studies in SMCs revealed that myocardin induced the activity of multiple SMC marker gene promoters including SM α-actin, SM-myosin heavy chain, and SM22α by 9- to 60-fold in a CArG-dependent manner, whereas myocardin short interfering RNA markedly decreased activity of these promoters. Moreover, adenovirus-mediated overexpression of a dominant-negative form of myocardin significantly suppressed expression of endogenous SMC marker genes, whereas adenovirus-mediated overexpression of wild-type myocardin increased expression. Taken together, results provide compelling evidence that myocardin plays a key role as a transcriptional coactivator of SMC marker genes through CArG-dependent mechanisms.

Control of SRF binding to CArG box chromatin regulates smooth muscle gene expression in vivo

Abstract: Precise control of SMC transcription plays a major role in vascular development and pathophysiology. Serum response factor (SRF) controls SMC gene transcription via binding to CArG box DNA sequences found within genes that exhibit SMC-restricted expression. However, the mechanisms that regulate SRF association with CArG box DNA within native chromatin of these genes are unknown. Here we report that SMC-restricted binding of SRF to murine SMC gene CArG box chromatin is associated with patterns of posttranslational histone modifications within this chromatin that are specific to the SMC lineage in culture and in vivo, including methylation and acetylation to histone H3 and H4 residues. We found that the promyogenic SRF coactivator myocardin increased SRF association with methylated histones and CArG box chromatin during activation of SMC gene expression. In contrast, the myogenic repressor Kruppel-like factor 4 recruited histone H4 deacetylase activity to SMC genes and blocked SRF association with methylated histones and CArG box chromatin during repression of SMC gene expression. Finally, we observed deacetylation of histone H4 coupled with loss of SRF binding during suppression of SMC differentiation in response to vascular injury. Taken together, these findings provide novel evidence that SMC-selective epigenetic control of SRF binding to chromatin plays a key role in regulation of SMC gene expression in response to pathophysiological stimuli in vivo.

Complex regulation and function of the inflammatory smooth muscle cell phenotype in atherosclerosis.

Abstract: Vascular smooth muscle cell (SMC) phenotypic modulation plays a key role in atherosclerosis and is classically defined as a switch from a 'contractile' phenotype to a 'synthetic' phenotype, whereby genes that define the contractile SMC phenotype are suppressed and proliferation and/or migratory mechanisms are induced. There is also evidence that SMCs may take on a 'proinflammatory' phenotype, whereby SMCs secrete cytokines and express cell adhesion molecules, e.g. IL-8, IL-6, and VCAM-1, respectively, which may functionally regulate monocyte and macrophage adhesion and other processes during atherosclerosis. Factors that drive the inflammatory phenotype are not limited to cytokines but also include hemodynamic forces imposed on the blood vessel wall and intimate interaction of endothelial cells with SMCs, as well as changes in matrix composition in the vessel wall. However, it is critical to recognize that our understanding of the complex interaction of these multiple signal inputs has only recently begun to shed light on mechanisms that regulate the inflammatory SMC phenotype, primarily through models that attempt to recreate this environment ex vivo. The goal of this review is to summarize our current knowledge in this area and identify some of the key unresolved challenges and questions requiring further study.

Macrophage plasticity and interaction with lymphocyte subsets: cancer as a paradigm

Abstract: Plasticity is a hallmark of cells of the myelomonocytic lineage. In response to innate recognition or signals from lymphocyte subsets, mononuclear phagocytes undergo adaptive responses. Shaping of monocyte-macrophage function is an essential component of resistance to pathogens, tissue damage and repair. The orchestration of myelomonocytic cell function is a key element that links inflammation and cancer and provides a paradigm for macrophage plasticity and function. A better understanding of the molecular basis of myelomonocytic cell plasticity will open new vistas in immunopathology and therapeutic intervention.

Molecular Regulation of Vascular Smooth Muscle Cell Differentiation in Development and Disease

Abstract: The focus of this review is to provide an overview of the current state of knowledge of molecular mechanisms/processes that control differentiation of vascular smooth muscle cells (SMC) during normal development and maturation of the vasculature, as well as how these mechanisms/processes are altered in vascular injury or disease. A major challenge in understanding differentiation of the vascular SMC is that this cell can exhibit a wide range of different phenotypes at different stages of development, and even in adult organisms the cell is not terminally differentiated. Indeed, the SMC is capable of major changes in its phenotype in response to changes in local environmental cues including growth factors/inhibitors, mechanical influences, cell-cell and cell-matrix interactions, and various inflammatory mediators. There has been much progress in recent years to identify mechanisms that control expression of the repertoire of genes that are specific or selective for the vascular SMC and required for its differentiated function. One of the most exciting recent discoveries was the identification of the serum response factor (SRF) coactivator gene myocardin that appears to be required for expression of many SMC differentiation marker genes, and for initial differentiation of SMC during development. However, it is critical to recognize that overall control of SMC differentiation/maturation, and regulation of its responses to changing environmental cues, is extremely complex and involves the cooperative interaction of many factors and signaling pathways that are just beginning to be understood. There is also relatively recent evidence that circulating stem cell populations can give rise to smooth muscle-like cells in association with vascular injury and atherosclerotic lesion development, although the exact role and properties of these cells remain to be clearly elucidated. The goal of this review is to summarize the current state of our knowledge in this area and to attempt to identify some of the key unresolved challenges and questions that require further study.

Mechanisms of NAFLD development and therapeutic strategies

Abstract: There has been a rise in the prevalence of nonalcoholic fatty liver disease (NAFLD), paralleling a worldwide increase in diabetes and metabolic syndrome. NAFLD, a continuum of liver abnormalities from nonalcoholic fatty liver (NAFL) to nonalcoholic steatohepatitis (NASH), has a variable course but can lead to cirrhosis and liver cancer. Here we review the pathogenic and clinical features of NAFLD, its major comorbidities, clinical progression and risk of complications and in vitro and animal models of NAFLD enabling refinement of therapeutic targets that can accelerate drug development. We also discuss evolving principles of clinical trial design to evaluate drug efficacy and the emerging targets for drug development that involve either single agents or combination therapies intended to arrest or reverse disease progression.