Regulation of the myogenic response and stretch-induced calcium signaling in the vascular wall: Novel insights into the role of microRNAs and protein tyrosine kinase 2

Abstract: Intraluminal pressure has a significant impact on vascular adaptability, phenotype and regulation of blood flow and
pressure. On one hand, increased pressure/stretch for a prolonged time can cause structural changes in vessel wall; on
the other hand, lack of pressure/stretch can promote a phenotype shift. This thesis investigates novel roles of
microRNAs and protein tyrosine kinase 2 in pressure/stretch-induced signaling mechanisms in the vascular wall.
Using two different knockout mouse models, we uncovered a novel role of microRNAs in the pressure-induced
myogenic response. We demonstrated that global deletion of smooth muscle-specific microRNAs causes a loss of
pressure-induced contraction and that this likely involves diminished calcium influx due to reduced stretch-induced
activation of the PI3K/Akt pathway. Similarly, global deletion of the smooth muscle enriched miRNA-143/145 also
depleted myogenic responses but this effect could be due to several combined factors including loss of calcium influx
and decreased expression of myosin light chain kinase. Furthermore portal veins of miRNA-143/145 KO mice exhibit
lack of stretch-induced contractile differentiation, which may in part be due to a reduced expression of L-type calcium
channels caused by an increased expression of the transcriptional repressor DREAM. Using a novel small molecule
inhibitor of PYK2, we demonstrated that PYK2 could distinguish between non-voltage and voltage-dependent calcium
pools to initiate signal transduction in the smooth muscle of portal vein. Inhibition of PYK2 can reduce phenotype
modulation and apoptosis in balloon injured carotid arteries.
In conclusion, we have established an indispensable role of microRNAs in the presssure-induced myogenic response
and maintainance of stretch-induced conctractile differentiation. Morover we have established that PYK2 is involved in
stretch-induced calcium handling in spontaneously active portal vein and in phenotypic shift of smooth muscle cells
following vascular injury.