Linda M. Callahan

Myotonic dystrophy (DM), the most common form of muscular dystrophy in adult humans, results from expansion of a CTG repeat in the 3' untranslated region of the DMPK gene. The mutant DMPK messenger RNA (mRNA) contains an expanded CUG repeat and is retained in the nucleus. We have expressed an untranslated CUG repeat in an unrelated mRNA in transgenic mice. Mice that expressed expanded CUG repeats developed myotonia and myopathy, whereas mice expressing a nonexpanded repeat did not. Thus, transcripts with expanded CUG repeats are sufficient to generate a DM phenotype. This result supports a role for RNA gain of function in disease pathogenesis.

Epidemiological and clinical studies suggest that nonsteroidal anti-inflammatory drugs (NSAIDs) that inhibit cyclooxygenase (COX) slow the progression and delay the onset of Alzheimer disease (AD). Two isoforms of cyclooxygenase have been identified. Although much effort has recently been focused on the inducible COX-2 isoform, little is known about COX-1 expression in human brain. We report that COX-1 message and immunoreactivity are localized to human hippocampal CA3 and CA4 neurons, granular neurons in neocortical layer IV, and occasional cortical pyramidal neurons. Quantitative in situ hybridization showed no differences between COX-1 mRNA levels in control and AD CA3 hippocampal neurons. COX-1 immunoreactivity was also present in microglial cells in gray and white matter in all brain regions examined. COX-1 appeared to be expressed in microglial cells regardless of their activation state as determined by HLA-DR immunostaining. However, COX-1 immunopositive microglia were found in association with Abeta plaques, and the density of COX-1 immunopositive microglia in AD fusiform cortex was increased. This pattern suggests an overall increase of COX-1 expression in AD. Currently used NSAIDs inhibit both isoforms of cyclooxygenase. The present study shows that COX-1 is widely expressed in human brain, and raises the possibility that COX-1 may contribute to CNS pathology.

Combining immunocytochemistry with in situ hybridization of Alzheimer disease (AD) hippocampus demonstrated a 50% reduction in grain density for synaptophysin message over CA1 pyramidal neurons containing neurofibrillary tangles (NFT) relative to near neighbor NFT-free neurons. This decrease was not global, but was selective since message grain density for the lysosomal protein, cathepsin D, increased 33% in these neurons (relative to NFT-free neurons). Poly A+ message grain density decreased by 25% in NFT neurons. Percent of the cell body containing NFT correlated -0.35 (p < 0.0001) with grain density for synaptophysin message. These data verify the concept of altered profiles of gene expression as a function of disease state within single cells and suggest that events associated with NFT formation may lead to altered expression of synaptic messages.