Our research program seeks to identify the cellular and molecular programs that are dysregulated in vascular disease with a focus on pulmonary arterial hypertension (PAH).  This condition can be a complication of a variety of medical diseases such as congenital heart defects, infectious and autoimmune disease and drugs and toxins. PAH can also arise as a disease of unknown etiology primarily in young women as well as in children. It is characterized by progressive loss and occlusion of the distal pulmonary microcirculation, and is associated with endothelial dysfunction, exuberant proliferation of de-differentiated smooth muscle-like cells, and chronic perivascular and intravascular inflammation, all contributing to increased resistance to flow and culminating in heart failure. There are treatments for PAH that improve survival and quality of life. The mainstay of therapies primarily dilate blood vessels, and newer and emerging  treatments are directed at the pathobiology. While all these treatments improve symptoms and survival there is still no cure for PAH. Our studies uses high throughput CRISPR and other genomic technologies, a variety of cell biology platforms (including confocal and video microscopy and cultured cells under flow conditions), genetically modified mouse models of human disease, human tissue samples from lung and blood and induced pluripotent stem cells (iPSCs) differentiated to vascular  and inflammatory cells to learn how we can activate molecular programs to regenerate lost microvessels and to reverse the obliterative changes in the pulmonary  circulation.   These studies are summarized below and described in greater detail under ‘Research Projects’.

Clinical Trials: Over the past decade our research has led to two novel compounds in clinical trial. Both agents suppress inflammation and activate signaling through the bone morphogenetic protein receptor (BMPR)2. The most common mutation associated with hereditary PAH is a mutation in BMPR2, and this receptor is deficient in patients and experimental models of PAH where there is no mutation described.  A Phase 1 trial with the elastase inhibitor human recombinant elafin (Tiprelestat supplied by tiakis) was completed with no toxicity in human subjects, and a Phase 2 study in PAH patients (a double blind two dose Tiprelestat and placebo control clinical trial) will begin in 2026. A derivatized   treatment using the immunosuppressant FK-506 will also be administered in Phase 2 Clinical Trial. Our studies encompass novel approaches to gene therapy in monogenic disorders where obstruction occurs in pulmonary arteries (e.g. JAG1 mutation in Alagille syndrome).

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Chronic Inflammation and Altered Immunity: We build on previous studies in the Rabinovitch Laboratory that revealed that loss of BMPR2 in endothelial cells increases GM-CSF resulting in enhanced monocyte recruitment. BMPR2 deficient monocytes have elevated STAT1 signifying a pro-inflammatory phenotype which can be attributed to an increase in expression of human endogenous retrovirus HERV-K. We are currently investigating how a reduction in BMPR2 de-methylates HERV-K and by the same mechanism involving phosphorylation of the methylase KAP1, perturbs the function of the long non-coding (lnc) RNA Xist in repressing inflammatory genes on the X chromosome.  We have further characterized PAH monocytes in studies that reveal increased trans-endothelial migration, and differentiation into monocyte derived dendritic cells that can induce smooth muscle cell (SMC) proliferation. Our more recent studies focus on how these proliferative SMC induce monocytes to become myofibroblasts. Neutrophils from patients with PAH also show increased transendothelial migration and propensity to release damaging neutrophil extracellular traps. HERV-K is also increased in these myeloid cells andthese retroviral elements can increase production of neutrophil elastase as part of an innate immune response, the sequelae of which can lead to PAH. Thus, suppressing neutrophil elastase activity and activation of HERV-K is a major focus of our studies.  

Genetics, Epigenetics and Metabolism in Pulmonary Arterial Hypertension:  We use induced pluripotent stem cells (iPSCs)-derived endothelial (EC), SMC and monocytes from PAH patients with a variety of ‘omics’ technologies as surrogates for native cells, to elucidate modifying factors that impact penetrance of a mutation in causing PAH, in collaboration with the Gifford lab.  In collaboration with the Engreitz and Qiu labs, we are applying innovative bioinformatics methods of analysis to integrate very large publicly available data sets with novel data sets derived from state-of-the-art transcriptomic and metabolomic technologies, to generate a powerful systems biology approach to characterize PAH and to find common aberrant pathways in the cells, that can be targeted therapeutically.  In so doing we have uncovered novel mechanisms underlying the propensity to unrepaired DNA damage in EC, proliferation in SMC and homing of inflammatory cells to the adventitia.  The impact of these abnormalities in causing vascular disease is tested in genetically modified mice and rats. We are using high throughput perturbation of genes and single cell analyses (Perturb-seq) to find common pathways of gene dysregulation and are observing common features of gene dysregulation with mutations in BMPR2, SOX17 and TBX4.  One lung EC geneTMEM100 appears to be pivotal in reproducing the abnormal sequelae of these mutations when it is dysregulated and in reversing them when it is replaced. 

The role of biomechanical forces in the normal modulation of EC function and plasticity is investigated using flow systems to study the impact of laminar flow, disturbed flow and high shear on endothelial cell chromatin structure, transcription factor accessibility and gene regulation. We study the pathological effects of high shear stress levels, such as observed in children predisposed to PAH associated with congenital heart disease or in small vessels that are occluded in idiopathic PAH. Companion studies use a mouse model of HSS induced by an aortocaval shunt to evaluate agents that can treat or reverse disease.  In collaboration with the Skylar-Scott lab, we are developing an in-vitro micro-physiological system mimicking the 3D multi-layer structure of endothelial and smooth muscle cells to study the disease mechanism and treatment of PAH. Free-standing vessels can be fabricated on a chip in situ based on 3D printing and tissue engineering technologies using a circular fibrin scaffold with smooth muscle cells embedded and lined by endothelial cells. By connecting the free-standing 3D tubular vessels array with a perfusion system, different shear stress and pulsatility of vessels can be tested. By using this platform, we can study gene expression changes and extracellular matrix remodeling in vessels according to the diverse genetic backgrounds. In collaboration with the Engreitz lab, we are applying novel genetic engineering tools to increase expression of JAG1 from the normal allele in patients with Alagille syndrome and halplinsufficiency of this gene owing to a heterozygous mutation.

Our research program is funded by the NIH and private foundations; please see our funded projects under https://med.stanford.edu/rabinovitchbland/research/funding-sources.html

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