New Mechanistic Insights to Hereditary Vascular Disease
The aorta is the largest artery in the human body responsible for delivering blood from the heart to the rest of the body. Aortic diseases are characterized by defects in the aorta and often, patients have no symptoms prior to their incidental diagnosis resulting from laboratory tests performed for other medical reasons. Thoracic aortic disease is caused by a weakening of the aortic wall that can cause enlargement and dilation, known as a thoracic aortic aneurysm, that over time can be at risk of tearing (dissection) or rupture. Aortic aneurysms, including both thoracic and abdominal aortic aneurysms, are the second most prevalent aortic disease behind atherosclerosis, and are the ninth‐leading cause of death globally.
Vascular smooth muscle cells (vSMC) are the predominant cell type within the aortic wall and dysregulation of vSMC functions contributes to aortic aneurysm (AA) and aortic dissection (AD) development and progression. In some cases, there is evidence to suggest an underlying genetic component and disease development. Researchers are investigating the potential causal relationship between genetic heritability and aortopathic disease that could lead to new treatments and preventative measures.
Does your research require the use of muscle cells? Lifeline® offers a variety of smooth muscle cells (SMCs) isolated from different tissues as well as primary skeletal muscle satellite cells. Click on the links below for more information on these cell types:
- Prostate SMCs
- Bronchial/Tracheal SMCs
- Lung SMCs
- Aortic SMCs
- Bladder SMCs
- Coronary artery SMCs
- Pulmonary artery SMCs
- Uterine SMCs
- Primary Human Skeletal Muscle Satellite Cells
New Research using Lifeline’s Aortic Smooth Muscle Cells
Hereditary aortopathic diseases such as heritable thoracic aortic disease (HTAD) and FTAAD (familial thoracic aortic aneurysm and dissection) are characterized by diverse genetic heterogeneity. The most widely used clinical genetic panels for aortopathy evaluates >20 genes but can only identify a causal genetic variant in 20% of patients. This means for most patients and families with a history of aortopathic diseases there is no identifiable genetic cause. Equally concerning is even when the genetic cause is known, the molecular mechanisms remain poorly understood.
In a recently published study by Koenig and Colleagues, a family with a history of aortopathic disease was studied to look at the underlying genetic cause and molecular mechanisms. Genetic testing of a 39-year-old individual (proband) and five family members (spanning 3 generations) identified an autosomal dominant novel pathogenic variant in the PLOD1 gene (c.534C>A (p. Ser178Arg). Given previous research indicating that PLOD1 is involved in HTAD/FTAAD, the authors aimed to investigate the impact of this genetic variant on vascular integrity and disease progression. PLOD1 encodes for lysyl hydroxylase-1 (LH1, also known as PLOD1), an enzyme required for the collagen formation, which provides the structure for vSMC stability needed to develop a mature ECM to sustain arterial integrity.
In looking at the collagen in the proband’s aorta, the researchers determined the collagen morphology to be most like elderly tissues and found evidence suggesting the rate of collagen turnover is diminished and that collagen post-translational modifications (PTM) are likely impacted. The location of the Ser178Arg mutation is in the N-terminal domain of PLOD1, corresponding to the glycosyltransferase (GT) catalytic site of the homologous multifunctional enzyme PLOD3. This prompted the researchers to test the glucosylgalactosyltransferase (GluT) activity of wildtype PLOD1, which was present but at significantly lower levels compared to PLOD3. Computational modeling combined with mutational analysis led the researchers conclude that malfunctions caused by the PLOD1 variant severely impacts mature collagen secretion and overall ECM organization.
In vitro studies to investigate the precise impact of the PLOD1 variant on functional changes on vSMCs was conducted with Lifeline’s human aortic smooth muscle cells, which were transfected with PLOD1 wildtype, the p. (Ser178Arg) variant or RNA silencing knockdown (siPLOD-1). The contractile function of the cells was evaluated with collagen gel-based contraction assays and gene expression of contractile, proliferative, and secretory markers of the variant was compared to both wild-type, knockdown siPLOD-1 transfected, and control vSMCs. The data from these experiments suggested that vSMCs can undergo phenotypic switching based on the level of endogenous PLOD1. In cases where there are low collagen levels, a secretory phenotype in vSMCs is favorable to increase collagen secretion and preserve ECM integrity. The authors speculate that abnormal enzyme folding caused by the PLOD1 variant impacts vSMC collagen secretion through its effect on proper collagen lysine glycosylation (PTM). The vSMCs dysfunction effectively reduced mature fibril formation and diminished the integrity of the ECM that could contribute to vascular pathogenicity.
The authors of the publication provide in vitro and in vivo functional data that suggest PLOD1 may impact arterial wall integrity through newly described GluT enzymatic roles and modulation of vSMC function. This study effectively links the p. (Ser178Arg) PLOD1 variant with identified molecular mechanism of action(s) that contributes to the observed and premature hereditable aortopathologies seen in the proband and family members. Additional research will be important to better understand the pathogenesis and identify potential future therapeutic targets for vascular connective tissue disease.
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