Fig. 3: A pathogenic premature termination codon (PTC) variant in THSD4 is associated with medial degeneration and activation of the TGFβ pathway.

(a–c) Histology of aortic media from the 48-year-old TAA-1839 proband (II:2), carrying the THSD4 p.(Ala468Glnfs*45) variant (middle) compared with a 54-year-old thoracic aortic aneurysm (TAA) female patient carrying the FBN1 p.(Cys2307Arg) variant (right) along with normal ascending aorta obtained from a 52-year-old female organ donor (left). Staining with hematoxylin–eosin (HE) (a), orcein (b), and Alcian Blue (c) revealed the characteristic features of medial degeneration: disorganization of the media with fragmented and disordered elastic fibers, accumulation of proteoglycans and smooth muscle cell (SMC) rarefaction in the individuals with the THSD4 and FBN1 variants. Scale bar, 25 µm. (d) Immunohistochemical analysis of the same tissues showed increased TGFβ1 expression, particularly around microvessels, in aortic tissue from the THSD4 and FBN1 variant carriers compared with normal aorta. Scale bar, 50 µm. (e) Aneurysmal tissue from individuals carrying THSD4 and FBN1 variants show a diffuse increase in nuclear pSmad2/3 expression in the most affected medial layer compared with control aortic tissue. Scale bar, 50 µm. (f) Immunofluorescent (red) fibrillin-1 is almost undetectable in healthy aorta. It appears as discontinuous, aggregated microfibrils parallel to elastic fibers in aortic tissue from the patients carrying the FBN1 p.(Cys2307Arg) and THSD4 p.(Ala468Glnfs*45) variants. Scale bar, 10 µm. (g) Fibronectin appears to be overexpressed in aneurysmal tissues compared with healthy aorta. The aneurysmal aortic sections showed condensed, pericellular fibronectin staining with some aggregates appearing around SMCs. Scale bar, 10 µm. Elastic fibers appear in green in (f, g) (autofluorescence).