PTGDR and Alzheimer disease: In AD patients and in Tg2576 mice, a well-established AD model (Hsiao et al., 1996), the levels of the PGD2 synthase H-PGDS and the PGD2 receptor DP1 were found to be selectively up-regulated in microglia and astrocytes within senile plaques (Mohri et al., 2007).