FLNB and atrial fibrillation: To further define the increase in TGFβ signaling activity, we quantified the in vivo expression of TGFβ signaling targets including Connective Tissue Growth Factor (CTGF) and p21, both of which are highly expressed in cartilage, by qPCR of RNA derived from Flnb+/+ and Flnb–/–P1 sternal cartilage as well as P15 IVD AF tissue [23–25].