Besides cardiomyocytes, crosstalking between cardiac fibroblasts and cardiomyocytes inhibits glucose metabolism enzyme activity and lactate transporter expression, possibly due to the fibroblast growth factor 21 (FGF21)-adiponectin pathway during aging-related heart failure.56,57 More importantly, defective glucose metabolism in the aging heart is correlated with immune activation in noncardiomyocytes. The gene discussed is FGF21; the disease is heart failure.