Structure and Survival of SST Interneurons in Dentate Granule Cell-pten KO Mice
Abstract number :
3.029
Submission category :
1. Basic Mechanisms / 1B. Epileptogenesis of genetic epilepsies
Year :
2024
Submission ID :
235
Source :
www.aesnet.org
Presentation date :
12/9/2024 12:00:00 AM
Published date :
Authors :
Presenting Author: Austin Drake, BS – University of Cincinnati College of Medicine
Justin Ruksenas, BS – Cincinnati Children's Hospital Medical Center
Lilian Jerow, BS – Cincinnati Children's Hospital Medical Center
Carlie McCoy, BS – Cincinnati Children's Hospital Medical Center
Steve Danzer, PhD – Cincinnati Children's Hospital Medical Center
Rationale: mTOR pathway mutations in the CNS produce a class of disorders collectively called mTORopathies, which are characterized by cognitive impairment and epilepsy. These diseases seem to develop in many patients following somatic mutations in excitatory neural progenitors, such that interneurons are not directly affected. Secondary changes among interneurons, however, are evident in patient samples and mTORopathy models. While the mechanisms by which interneurons regulate healthy neurons are well-characterized, how these interneurons regulate mTOR hyperexcitable neurons is not well understood. In this study, we histologically investigated the structure and survival of hippocampal somatostatin-expressing (SST) interneurons in a model in which epilepsy develops following deletion of phosphatase and tensin homologue (Pten) from a subset of dentate granule cells.
Methods: On postnatal day 14, quadruple transgenic Gli1-CreERT2, Ptenfl/fl, SST-FlpO+/-, eGFP+/- (n=6) and control mice (n=5) were injected with tamoxifen to allow for CreERT2-mediated deletion of Pten from >10% of DGCs. An added FLP-FRT strategy enabled endogenous GFP labeling of SST interneurons. At 10 weeks of age, tissue was collected and histological experiments were conducted. This included assessing SST interneuron structure and markers of neuronal activity.
Results: Pten deletion from DGCs resulted in reduced hippocampal SST interneuron density (Control, 2176 ± 97 cells/mm3; KO, 1901 ± 68 cells/mm3; p=0.0402), with significant loss in the hilus (Control, 4395 ± 182; KO, 3411 ± 322; p=0.0334) and CA1 (Control, 2217 ± 101; KO, 1853 ± 59; p=0.0102). Surviving hilar SST interneurons exhibited enlarged somas (Control, 131 ± 7 μm2; KO, 159 ± 7 μm2; p=0.0225), but similar numbers of proximal dendrites and cell roundness, suggesting similar structure outside of cellular hypertrophy. To histologically evaluate neuronal activity, we immunostained for c-Fos and FosB. SST interneurons in both groups rarely co-labeled with c-Fos, and did not differ statistically (Mann-Whitney test, p= >0.99). Pten KO mice, however, exhibited a higher proportion of FosB+ SST interneurons (Control, 7.4 ± 1.2%; KO, 49.6 ± 11.5%; p=0.0092). There were also fewer c-Fos+ DGCs (Control, 139 ± 24 cells/mm2; KO, 43 ± 13 cells/mm2; p=0.0025), but a greater proportion of FosB+ DGCs (Control, 29.2 ± 4.1%; KO, 66.7 ± 10.4%; p=0.0127) in Pten KO mice. Ongoing work will compare DGC innervation onto SST interneurons in Pten KO and control conditions.
Conclusions: Endogenous labeling of SST-expressing interneurons provided an effective means of fate-mapping this sub-population of interneurons. Our results demonstrate that there is loss of hippocampal SST interneurons in Pten KO mice, particularly in the hilus and CA1, with morphological changes and evidence of altered activity in surviving interneurons. This study advances our understanding of the interplay between aberrant excitatory neurons and neighboring inhibitory interneurons.
Funding: R01-NS-065020 and R01-NS-121042
Basic Mechanisms