Dr. Peter A. Doris
The University of Texas Health Science Center at Houston
Institute of Molecular Medicine
Research Center for Human Genetics
- Genetics and pathophysiologic mechanisms of common cardiovascular diseases
- The genetic basis of susceptibility that causes increased renal sodium reabsorption and the mechanisms by which this leads to increased blood pressure.
Work in this laboratory has shown that expression of genes and abundance of proteins involved in active sodium reabsorption in the kidney is altered in the genetic model of hypertension we are studying (SHR). Our data shows that this changes is probably due to a defect in control of the activity of a sodium reabsorbing protein which involves mis-targeting of protein to the basolateral membrane of the proximal nephron, the site where most sodium reabsorption takes place.
A number of investigative schemes are being used to probe abnormal renal sodium reabsorption in genetic hypertension. Most genetic approaches to disease use the reductionist method to identify and refine single chromosomal loci and specific genes contained within them. The reductionist approach has been slow to prove its benefit to complex disease genetics where multiple and perhaps interactive genes simultaneously operate to produce the disease phenotype. The development of global and comprehensive investigative systems (gene expression arrays and quantitative proteomics technologies) provide a new method to explore the genetic mechanism in an integrated manner. We have used Affymetrix gene expression arrays to uncover a number of new pathways in the renal mechanism of high blood pressure. Similarly proteomic approaches to investigate very large numbers of proteins either expressed by tissues or localized to specific cellular compartments within a tissue are being employed (see figure). The genes in these pathways are being mapped and their contribution to the inheritance of high blood pressure is being investigated. Variations in gene sequence (single nucleotide polymorphisms, SNPs) that may alter the function of proteins, thereby leading to increased renal salt retention, have been discovered using an efficient gene screening technique called denaturing HPLC and the relevance of these SNPs to blood pressure elevation is being examined.
Quantitative proteomics using 2-D gel electrophoresis and Cy-dye trace labeling of proteins. Kidney proteins from normotensive and genetically hypertensive rats were labeled with Cy2 and Cy3 respectively. A reference sample containing equal aliquots of all replicates in the experiment was labeled with Cy5 and all three samples were run on a single 2-D gel. The reference sample served as an internal quantitative control for all gels in the experiment. Differentially abundant proteins are shown as red (up) or blue (down) spots. Proteins creating spots with statistically significant abundances across replicate gels were identified by mass spectrometry using the ABI 4700 TOF-TOF instrument.
Our laboratory has begun to elucidate important features of a new cardiotonic steroid hormone that influences sodium reabsorption, contraction of blood vessels and growth of heart and vascular tissue and kidney epithelial cells. Cardiotonic steroid glycoside drugs, derived from plant sources, have been a mainstay of pharmacological therapy for heart failure for many years. We have discovered that the mammalian adrenal cortex is the site of production of this novel cardiotonic steroid hormone. This hormone provides a much sought-after mechanistic link between abnormal sodium reabsorption by the kidney and the genesis of high blood pressure. We have shown that the adrenal cardiotonic steroid is synthesized in a novel biosynthetic pathway distinct from that of known adrenocortical hormones, all of which result from products of a single chemical reaction: cholesterol side chain cleavage. The new hormone is made by a separate biosynthetic reaction that branches from the production of other adrenal hormones.
We are using pharmacological inhibitors and genetically modified adrenocortical cells to map out the biosynthetic pathway. The control of cardiotonic steroid production by agents that integrate cardio-renal function, such as dopamine, angiotensin and atrial natriuretic peptide has been shown and the second messenger pathways and integration of these regulatory circuits is being determined. Understanding the chemistry and the control of production and release of this new adrenal steroid may provide new approaches to treat high blood pressure. We now have evidence that this hormone also acts as a growth factor in the cardiovascular system and kidney. The growth stimulatory effect is independent of inhibition of sodium transport. It involves activation of intracellular signaling cascades that stimulate proliferation through activation of MAP kinases. The pleiotropic effects of this hormone have very broad implications: it's ability to increase renal sodium excretion and arterial pressure maybe reinforced by proliferative effects on renal and cardiovascular cell biology that support the adaptive response of these systems to elevated blood pressure.
Program in Cell and Regulatory Biology (Physiology Track)
Office: IMM/SRB 530F
Title: Associate Professor
Ph.D. - University of California-Riverside - 1981