Differential cellular expression of neurotrophins in cortical tubers of the tuberous sclerosis complex

Neurotrophins. and their receptors modulate cerebral cortical development. Tubers in the tuberous sclerosis complex (TSC) are characterized histologic ally by disorganized cortical cytoarchitecture and thus, we hypothesized th at expression of neurotrophin mRNAs and proteins might be altered in tubers . Using in situ transcription and mRNA amplification to probe cDNA arrays, we found that neurotrophin-3 (NT3) and trkB mRNA expression were reduced wh ereas neurotrophin-4 (NT4) and trkC mRNA expression were increased in whole tuber sections. Alterations in mRNA abundance were defined in single micro dissected dysplastic neurons (DNs) and giant cells (GCs). NT3 mRNA expressi on was reduced in GCs and trkB mRNA expression was reduced in DNs. NT4 mRNA expression was increased in DNs and trkC mRNA expression was increased in both DNs and GCs. In three patients, TSC2 locus mutations were confirmed an d the mean tuberin mRNA expression levels was reduced across all nine cases . Consistent with these observations, NT3 mRNA expression was reduced but t rkC mRNA expression was increased in vitro in human NTera2 neurons (NT2N) t ransfected with a tuberin antisense construct that reduced tuberin expressi on. Western analysis of tuber homogenates and computer-assisted densitometr y of immunolabeled sections confirmed the neurotrophin mRNA expression data in whole sections and single neurotrophin immunoreactive cells. We conclud e that alterations in NT4/trkB and NT3/trkC expression may contribute to tu ber formation during brain development as downstream effects of the hamarti n and tuberin pathway in TSC.