Expression of proNGF and its receptors p75^NTR and SorCS2 are coordinately up-regulated after myocardial ischemia in humans and mice. (A) Immunohistochemical detection of the prodomain of proNGF demonstrates increased proNGF reactivity in both cardiomyocytes and in vascular smooth muscle cells (arrow) in the peri-infarct region of the hearts of patients that died from recent MI (post-MI, right) compared with patients that died of noncardiac related causes (control, right). (B) Immunohistochemical detection of p75^NTR demonstrates induction of p75^NTR in mural cells of arterioles in post-MI patients (right, arrow) compared with noncardiac patients (control, left). Arrowhead indicates p75^NTR positive nerve fiber. (C) Quantification of proNGF immunoreactivity in cardiac myocytes of noncardiac patients and from the peri-infarct region of post-MI patients. ProNGF immunoreactivity in cardiomyocytes was quantified using a semiquantitative method in which 10 fields of view were scored by a blinded individual. Each field of view was given a score of 0–4: 0 for absence of immunoreactivity, 1 for weak immunoreactivity, 2 for modest immunoreactivity, 3 for moderate immunoreactivity, and 4 for strong immunoreactivity. The scores from the fields of view were averaged. (D and E) Quantification of proNGF and p75^NTR immunoreactivity in the cardiac arteries (D) and veins (E) of the peri-infarct region of post-MI patients and noncardiac patients. The number of proNGF or p75^NTR positive vessels is presented as a percentage of total vessels counted. The scores were averaged and the error bars represent the SEM. *, P < 0.05; ***, P < 0.001. (F) Immunohistochemical detection of SorCS2 demonstrates induction of SorCS2 in the cardiac vasculature (arrow) of post-MI patients compared with noncardiac patients. (G) Immunohistochemical detection of the prodomain of proNGF demonstrates increased proNGF reactivity in the infarct and peri-infarct regions of the mouse heart after I-R surgery (24 h I-R, right, arrow indicates proNGF-positive vascular smooth muscle cells) compared with sham-operated animals (24 h sham, left). (H) Immunohistochemical detection of p75^NTR in the mouse heart after I-R reveals induction of cell-associated p75^NTR (right, arrows) compared with hearts from sham-operated mice in which p75^NTR is primarily detected in cardiac nerve fibers (left). (A–F) n = 6 patients that died after myocardial ischemia, and five patients that died of noncardiac causes (G and H) n = 3–4 mice/group. Bars, 50 µm.