Comparison of natriuretic peptide receptor 2 (Npr2) and Npr3 expression in non-diseased (grade 0/I) and diseased (grade III to IV) cartilage. Tissues were taken from donors aged 55 to 60 and 80 to 85 years. Paraffin-embedded sections from a single donor aged 60 years were stained with Npr2 or Npr3 antibodies (green) and examined by immunofluoresence microscopy (A). Nuclei (blue) were stained with 4',6-diamidino-2-phenylindole (DAPI). Scale bar represents 10 μM. Negative controls showed no staining (not shown). Inset shows Npr2 (110 kDa) and Npr3 expression (60 kDa) by western blot analysis from the same donor. GAPDH, glyceraldehyde-3-phosphate dehydrogenase.