Glial changes in the dentate gyrus of neuronal-specific PTEN knockout mice correlate with changes in cell proliferation

Dysregulated hippocampal neurogenesis is a feature of temporal lobe epilepsy (TLE), marked by increased neuronal proliferation. The tumor suppressor gene phosphatase and tensin homolog (PTEN) regulates neuronal proliferation, and its deletion is implicated in TLE. We have previously shown that deletion of neuronal subset-specific (NS)-PTEN in mice increases the number of proliferating cells throughout the dentate gyrus, including subregions that are typically devoid of neurons but rich in glial cells, most notably the Hilus and Molecular Layer. In this study, we hypothesized that NS-PTEN knockout mice would exhibit increased numbers of microglia and astrocytes in these same dentate gyrus subregions. We performed immunohistochemistry for Iba1 (microglia) and GFAP (reactive astrocytes) on wild-type and NS-PTEN knockout mice at 4 and 10 weeks of age. Our data reveal that NS-PTEN knockout mice exhibit increased Iba1+ cell density at both ages, with some male-specific effects. Subregional analysis of the dentate gyrus showed that at 4 weeks, NS-PTEN knockout mice had greater Iba1+ cell density in the Granule Cell Layer (GCL) and Hilus, and at 10 weeks, increases were observed in the GCL, Hilus, and Molecular Layer. Additionally, we observed an increased number of microglia with an amoeboid morphology and fewer with thin, ramified processes. Contrast to Iba1+ microglia, GFAP+ reactive astrocytes were localized to the neurogenic GCL. Importantly, increases in both glial types strongly correlated with heightened cell proliferation (Ki67+ cells), as reported in our previous study, underscoring the role of glial cells in the spatial dysregulation of neurogenesis in NS-PTEN knockout mice.