REN and aneurysm: Though early studies reported increased activation of the TGF-β signaling pathway as the key mechanism in aneurysm formation, more recent data from mouse models and human genetic studies reveal a dual role of TGF-β signaling in aneurysm formation, depending on, e.g., the developmental origin of VSMCs, and suggest that additional mechanisms and pathways may be involved, such as the renin–angiotensin system and cytoskeleton dynamics [23,24,25].