Abstract
Sympathetic denervation of the heart following ischemia/reperfusion induced myocardial infarction (MI) is sustained by chondroitin sulfate proteoglycans (CSPGs) in the cardiac scar. Denervation predicts risk of sudden cardiac death in humans. Blocking CSPG signaling restores sympathetic axon outgrowth into the cardiac scar, decreasing arrhythmia susceptibility. Axon growth inhibition by CSPGs can depend on the sulfation status of the glycosaminoglycan (CS-GAG) side chains. Tandem sulfation of CS-GAGs at the 4th (4S) and 6th (6S) positions of n-acetyl-galactosamine inhibits outgrowth in several types of central neurons, but we don't know if sulfation is similarly critical during peripheral nerve regeneration. We asked if CSPG sulfation prevented sympathetic axon outgrowth after MI. Reducing 4S with the 4-sulfatase enzyme Arylsulfatase-B (ARSB) enhanced outgrowth of dissociated rat sympathetic neurons over CSPGs. Likewise, reducing 4S with ARSB restored axon outgrowth from mouse sympathetic ganglia co-cultured with cardiac scar tissue. We quantified enzymes responsible for adding and removing sulfation, and found that CHST15 (4S dependent 6-sulfotransferase) was upregulated, and ARSB was downregulated after MI. This suggests a mechanism for production and maintenance of sulfated CSPGs in the cardiac scar. We decreased 4S,6S CS-GAGs in vivo by transient siRNA knockdown of Chst15 after MI, and found that reducing 4S,6S restored tyrosine hydroxylase (TH) positive sympathetic nerve fibers in the cardiac scar. Reinnervation reduced isoproterenol induced arrhythmias. Our results suggest that modulating CSPG-sulfation after MI may be a therapeutic target to promote sympathetic nerve regeneration in the cardiac scar and reduce post-MI cardiac arrhythmias.