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Cardiovascular Engineering

Cardiovascular Engineering - Poster Session E

Poster H12 - Shear stress-mediated Inflammation Regulates BMPRII expression in the Aortas of Mice with Sickle Cell Disease

Saturday, October 26, 2024
10:00 AM – 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  ): Sickle cell disease (SCD) is a genetic disorder caused by a mutation in the β-globin allele and characterized by hemoglobin polymerization forming sickle-shaped red blood cells. An overlooked aspect of SCD is the chronic inflammatory state shown by increased monocyte and cell adhesion, which increases with SCD severity. Previously, we showed that endothelial cathepsin K is upregulated by monocyte adhesion isolated from people with sickle cell disease, while bone morphogenic protein receptor type II (BMPRII) is downregulated in areas of disturbed flow, where inflammation is more likely to persist. We also showed that increased cathepsin K expression in mouse models of sickle cell disease induced arterial expansion, medial wall thinning, and elastic lamina fragmentation in carotid arteries. Thus, we hypothesized BMPRII and cathepsin K are regulated in opposite directions by disturbed flow and inflammation, which is exacerbated in sickle cell disease. Therefore, we compared protein levels of BMPRII and cystatin C, an inhibitor of cathepsins, between abdominal aortas which are exposed to disturbed blood flow and thoracic aortas which experience more unidirectional flow from mouse models of sickle cell disease (AA, non-SCD; AS, sickle trait; SS, sickle cell genotype). Furthermore, the relationship between BMPRII and cathepsin K is investigated using aortas from cathepsin K knockout and cathepsin K positive mice with or without SCD.

Materials and

Methods:  Genotyped Townes Sickle cell model mice were dissected to obtain whole aortas, abdominal aortas, and thoracic aortas. Thoracic aortas were designated as above the diaphragm and abdominal aortas were designated being below the diaphragm. Aorta samples were lysed and homogenized using MP Bio’s bead beating lysis system while suspended in lysis buffer. Aorta samples were sonicated then centrifuged. BCA assays were used to determine protein concentration. Equal amounts of protein were loaded during SDS-PAGE and transferred to a nitrocellulose membrane using Bio-Rad’s semi-dry transfer system. Unconjugated antibodies were used to probe protein expression and were quantified using ImageJ.

Results, Conclusions, and Discussions: To examine how BMPRII is differentially expressed between SS and AA mice immunoblots were run comparing whole aortas. Contrary to our hypothesis, within littermate controls, SS mice showed greater BMPRII expression when compared to AA control mice. To test the hypothesis that BMPRII expression will be upregulated in thoracic aortas when compared to abdominal aortas, immunoblots for BMPRII were run comparing genotype-matched thoracic and abdominal aortas. Thoracic aortas showed higher BMPRII expression when compared to genotype-matched abdominal aortas (Fig 1A and 1B), which collaborates with our previous finding that unidirectional flow increases BMPRII expression compared to disturbed flow. To examine a link between BMPRII expression and cathepsin K presence, we examined aortic BMPRII expression from cathepsin K knockout mice with same sickle cell genotype and cathepsin K positive mice. BMPRII increased in cathepsin K knock out compared to cathepsin K positive mice in both AS and SS mice (Fig 1C and 1D), which could indicate a preservative function of cathepsin K knock out by increasing BMPRII expression. The presented data complicates our current understanding of BMPRII expression, in which inflammation decreases its expression since aortas from SS mice increased BMRPII expression. BMPRII expression is decreased in pulmonary hypertension where medial wall thickening and vasoconstriction in pulmonary arteries has been shown. On the contrary, medial wall thinning and arterial expansion has been shown in Townes mouse model of sickle cell disease. Thus, we postulate that a factor associated with arterial expansion and medial wall thinning is responsible for the upregulation of BMPRII in SS mice.

Acknowledgements (Optional):