Artery biomechanics and vascular damage in sickle cell disease

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Sickle cell disease (SCD) affects approximately 100,000 people in the U.S. but 300,000 babies are born with SCD every year globally. Currently few pharmaceutical options are available as a therapy, and life expectancy is still low for these individuals. Consequences of accelerated arterial damage include a 221-fold increased risk of strokes in children and then increased risk of hemorrhagic strokes during the third decade of life. Elastic lamina fragmentation were hallmarks identified in autopsy specimens of children with SCD, but underlying mechanisms are unclear and therefore cannot be prevented. Cysteine cathepsins are powerful proteases implicated in elastin and collagen degradation in cardiovascular disease (i.e. atherosclerosis). It was recently published by the PIs that cathepsins are similarly active in a transgenic sickle cell mouse model, and inhibition of JNK signaling blocked this as well as pathological arterial remodeling and biomechanical consequences. The long term goal is to identify novel therapeutic targets to inhibit proteolytic activity and cellular mechanisms that cause accelerated elastin and collagen degradation and pathological biomechanics in arteries of children and adults with SCD, and determine accumulated damage as they age. The objective is to investigate cathepsin-mediated arteriopathy and pathological biomechanical changes in large arteries due to SCD causing irreparable damage, and if curative bone marrow therapies prevent further arterial remodeling. Based on preliminary data and published studies, the central hypothesis is that cathepsin-mediated elastinolytic and collagenolytic activity in large arteries is JNK-dependent and downstream of the chronic inflammation (TNFα and monocytosis) caused by sickle cell disease. This hypothesis will be tested according to the following aims: Aim 1. To determine roles of cathepsin K in elastic lamina and collagen degradation by SCD as mice age and accumulate damage to arteries using a new mouse model that was generated by the investigators that is transgenic for sickle cell disease but null for cathepsin K. Aim 2. To improve JNK inhibition strategies that downregulate cathepsin expression and protect arterial integrity. Aim 3. To determine efficacy of curative BMT in preventing further arterial damage, and the need for further pharmaceutical interventions. This work is significant because its success will identify mechanisms to preserve integrity of arteries that undergo progressive damage over a lifetime with SCD even after curative bone marrow transplants. Innovative aspects include: 1) Studying arterial remodeling complications of SCD as opposed to the deoxygenated post-capillary venules and microcirculation that has dominated the field; 2) decomposing collagen degradation from elastin fragmentation and impact on arterial mechanics in SCD; and 3) identifying critical ages by which maintenance of vascular integrity may offer improved chance of preventing future cardiovascular and cerebrovascular complications, impacting quality and duration of life of those living with the genetic disorder sickle cell disease.