Cultured astrocytes have been previously found to express several neuropeptides, as well as the neuropeptide processing enzyme carboxypeptidase E (CPE). To investigate whether cultured astrocytes contain additional peptide-processing enzymes, Northern blots were screened for peptidylglycine-α-amidating monooxygenase (PAM) mRNA. PAM is involved with the formation of amide groups on the C-terminus of numerous peptide hormones and neurotransmitters. Primary cultures of astrocytes contain moderate levels of PAM mRNA, as determined by Northern blot analysis. The level of PAM mRNA is cultured hypothalamic astrocytes is similar to the level expressed in cultured hypothalamic neurons. The relative abundance of PAM mRNA differs up to 6-fold between astrocytes cultured from various brain regions. Astrocytes cultured from hypothalamus have high levels of PAM mRNA, those cultured from striatum, frontal cortex, and hippocampus have moderate levels, and those cultured from cerebellum have low levels. To investigate whether all cultured astrocytes express PAM mRNA, in situ hybridization analysis of cultured astrocytes was performed. Interestingly, virtually all of the astrocytes cultured from either hypothalamus or cerebellum express PAM mRNA, in contrast to a previous finding that only 20-40% of similarly cultured astrocytes express CPE. The presence of PAM mRNA in cultured astrocytes suggests that these cells have the capacity to produce amidated neuropeptides.
- Neuropeptide biosynthesis
- Prohormone processing