The BMP2 nuclear variant, nBMP2, is expressed in mouse hippocampus and impacts memory

Abstract

The novel nuclear protein nBMP2 is synthesized from the BMP2 gene by translational initiation at an alternative start codon. We generated a targeted mutant mouse, nBmp2NLS^tm, in which the nuclear localization signal (NLS) was inactivated to prevent nuclear translocation of nBMP2 while still allowing the normal synthesis and secretion of the BMP2 growth factor. These mice exhibit abnormal muscle function due to defective Ca²⁺ transport in skeletal muscle. We hypothesized that neurological function, which also depends on intracellular Ca²⁺ transport, could be affected by the loss of nBMP2. Age-matched nBmp2NLS^tm and wild type mice were analyzed by immunohistochemistry, behavioral tests, and electrophysiology to assess nBMP2 expression and neurological function. Immunohistochemical staining of the hippocampus detected nBMP2 in the nuclei of CA1 neurons in wild type but not mutant mice, consistent with nBMP2 playing a role in the hippocampus. Mutant mice showed deficits in the novel object recognition task, suggesting hippocampal dysfunction. Electrophysiology experiments showed that long-term potentiation (LTP) in the hippocampus, which is dependent on intracellular Ca²⁺ transport and is thought to be the cellular equivalent of learning and memory, was impaired. Together, these results suggest that nBMP2 in the hippocampus impacts memory formation.