Myocardial recovery from ischemia is impaired in CD36-null mice and restored by myocyte CD36 expression or medium-chain fatty acids

Abstract

Long-chain fatty acid uptake, which provides a large part of myocardial energy, is impaired in human and murine hearts deficient in the membrane fatty acid translocase, FAT/CD36. We examined myocardial function in CD36-null mice using the working heart. Fatty acid oxidation and stores of glycogen, triglycerides, and ATP were reduced in CD36-deficient hearts and were restored to WT levels by rescue of myocyte CD36. Under normal perfusion conditions, CD36-null hearts had similar cardiac outputs and end-diastolic pressures as WT or transgenic hearts. After 6 min of ischemia, cardiac output decreased by 41% and end diastolic pressure tripled for CD36-null hearts, with no significant changes in WT or transgenic hearts. Null hearts also failed more frequently after ischemia as compared with WT or transgenics. To dissect out contribution of fatty acid uptake, a perfusate-lacking fatty acids was used. This decreased cardiac output after ischemia by 30% in WT hearts as compared with 50% for CD36-deficient hearts. End diastolic pressure, a negative index of myocardial performance, increased after ischemia in all heart types. Addition to the perfusate of a medium-chain fatty acid (caprylic acid) that does not require CD36 for uptake alleviated poor ischemic tolerance of CD36-null hearts. In summary, recovery from ischemia is compromised in CD36-deficient hearts and can be restored by CD36 rescue or by supplying medium-chain fatty acids. It would be important to determine whether the findings apply to the human situation where polymorphisms of the CD36 gene are relatively common.

Fig. 1.

Cardiac expression of CD36 protein in different mouse models. Heart sections were prepared and incubated with polyclonal antibody against CD36 followed by a fluorescein-conjugated goat anti-rabbit IgG. Confocal images (equal exposure time) are shown. (A) WT. (B) CD36-null. (C) CD36 GR.

Fig. 2.

Palmitate oxidation and glucose uptake before and after transgenic rescue of CD36. (A) Palmitate oxidation rates of isolated cardiomyocytes from WT, CD36-null (KO), and CD36 rescued (GR) mice were determined at a FA/BSA ratio of 0.67. Data are means ± SEM (n = 6 per group). *, Significantly different from WT and GR (P < 0.01). (B) ¹⁸F-2-FDG uptake in WT, CD36-null, and GR hearts. Mice were injected with 12 μCi of ¹⁸F-2-FDG in a lateral tail vein. Hearts were removed, weighed, and counted for ¹⁸F-2-FDG radioactivity 120 minutes after injection; uptake rate is expressed per gram of wet tissue. Data are means ± SEM (n = 3 per group). *, Significantly different from WT and GR (P < 0.02).

Fig. 3.

Cardiac output pre- and postischemia in hearts with or without CD36-Cardiac output of WT, CD36-null (KO), and CD36 rescued (GR) mice are shown in A as a function of increasing preload pressures (mmHg). Hearts, perfused with bicarbonate buffer (KB) with and without FA were compared before and after 6 min of global ischemia and 8 min of reperfusion. (B) A comparison of cardiac output across groups at 15 mmHg of preload pressure is shown. *, Significantly different from WT and GR (P < 0.01).

Fig. 4.

End-diastolic pressure pre- and postischemia in hearts with or without CD36. End-diastolic pressure of hearts from WT, CD36-null (KO), and GR mice were evaluated at increasing preload pressure (A). Hearts, perfused with bicarbonate buffer (KB) with and without FA, were compared before and after 6 min of global ischemia and 8 min of reperfusion. (B) A comparison across groups is shown, with end-diastolic pressure at 15 mmHg of preload pressure. *, Significantly different from WT and GR (P < 0.01).

Fig. 5.

Effect of caprylic acid in the perfusate on cardiac tolerance to ischemia. Hearts from WT and CD36-null (KO) were perfused with KB buffer containing palmitate or caprylic acid. Recovery from ischemia was assessed and compared with hearts that were perfused with bicarbonate buffer without FA. Cardiac function is shown as the ratio of postischemic to preischemic values, with 100% representing the preischemic values. (A) Cardiac output. (B) End-diastolic pressure. *, Significantly different from “No FA” condition (P < 0.01). †, Significantly different from “Palmitate” condition (P < 0.01).