Melatonin promotes neuroblastoma cell differentiation by activating hyaluronan synthase 3‐induced mitophagy

Neuroblastoma is the second most common pediatric malignancy and has a high rate of spontaneous remission. Uncovering the mechanisms underlying neuroblastoma cell differentiation is critical for therapeutic purposes. A neuroblastoma cell line (N2a) treated with either serum withdrawal (<2.5%) or melatonin (>0.1 nmol/L) for 24 hours was used as a cell differentiation research model. Interestingly, the hyaluronan synthase 3 (HAS3) protein was induced in differentiated N2a cells. N2a‐allografted nude mice received an intraperitoneal injection of melatonin (40 or 80 mg/kg/day for 3 weeks). The mean tumor volume in mice treated with 80 mg/kg melatonin was smaller than that in PBS‐treated mice (1416.3 and 3041.3 mm(3), respectively, difference = 1625 mm(3), *P = 0.0003, n = 7 per group). Compared with the vector control group, N2a cells with forced HAS3 overexpression showed significantly increased neuron length (*P = 0.00082) and neurite outgrowth (*P = 0.00059). Intracellular changes in autophagy, including distorted mitochondria with abnormal circular inner membranes, were detected by transmission electron microscopy (TEM). Our study demonstrated that HAS3‐mediated signaling activated by physiological concentrations of melatonin (>0.1 nmol/L) triggered significant N2a cell differentiation. These results provide molecular data with potential clinical relevance for therapeutic drug development.