MALDI-mass spectrometry imaging identifies vitronectin as a common constituent of amyloid deposits

Abstract

Amyloids are pathological intra- and extracellular fibrillar aggregates of polypeptides with a cross-β-sheet structure and characteristic tinctorial properties. The amyloid deposits commonly enclose several non-fibrillar components of the extracellular matrix. Their potential to regulate the formation and aggregation process of amyloid fibrils is still poorly understood. For a better understanding of the role of the extracellular matrix in amyloidosis, it is essential to gain deeper insights into the composition of amyloid deposits. Here, we utilized matrix-assisted laser desorption and ionization mass spectrometry imaging to identify extracellular matrix compounds in amyloid deposits. Using this technique, we identified and determined the spatial distribution of vitronectin within AApoAI-, ALλ-, ATTR- and AIns amyloid deposits and, using immunohistochemistry, validated the spatial overlap of vitronectin with amyloids in 175 cases with diverse types of amyloid in several different tissues.

Keywords: amyloid; formalin-fixed/paraffin-embedded tissue; immunohistochemistry; mass spectrometry imaging; matrix-assisted laser desorption/ionization; vitronectin.

Figure 1.

Immunohistochemical staining of apoAI (A) and vitronectin (VTN; E) shows high intensity staining for amyloid deposits in formalin-fixed, paraffin-embedded amyloidogenic liver tissue sections. MALDI-MS images display the spatial distribution of tryptic peptides belonging to VTN (B−D), SAP (F) and apoE (G, H) within the tissue section. For all peptides, high signal intensities were detected in the amyloid deposits. The MALDI-MS/MS spectrum (I) displays the fragmentation pattern of the tryptic peptide at m/z 1646 identified as VTN. Scale, 2 mm.

Figure 2.

The presence of vitronectin within amyloid deposits is illustrated for several amyloid types: AA- and AFib amyloid both in kidney; ALλ- and ATTR amyloid in the large intestine; Aβ amyloid in brain; AIns amyloid in subcutaneous fat; Aβ2M amyloid in carpal tunnel ligament; and ALκ amyloid in liver. Congo red staining is observed with fluorescence microscopy, displaying amyloid deposits in orange. The case of AIns amyloid demonstrates that the distribution of vitronectin does not always cover the whole amyloid area. Scale, 80 µm.