Enriched environment ameliorates adult hippocampal neurogenesis deficits in Tcf4 haploinsufficient mice

Abstract

Background: Transcription factor 4 (TCF4) has been linked to human neurodevelopmental disorders such as intellectual disability, Pitt-Hopkins Syndrome (PTHS), autism, and schizophrenia. Recent work demonstrated that TCF4 participates in the control of a wide range of neurodevelopmental processes in mammalian nervous system development including neural precursor proliferation, timing of differentiation, migration, dendritogenesis and synapse formation. TCF4 is highly expressed in the adult hippocampal dentate gyrus - one of the few brain regions where neural stem / progenitor cells generate new functional neurons throughout life.

Results: We here investigated whether TCF4 haploinsufficiency, which in humans causes non-syndromic forms of intellectual disability and PTHS, affects adult hippocampal neurogenesis, a process that is essential for hippocampal plasticity in rodents and potentially in humans. Young adult Tcf4 heterozygote knockout mice showed a major reduction in the level of adult hippocampal neurogenesis, which was at least in part caused by lower stem/progenitor cell numbers and impaired maturation and survival of adult-generated neurons. Interestingly, housing in an enriched environment was sufficient to enhance maturation and survival of new neurons and to substantially augment neurogenesis levels in Tcf4 heterozygote knockout mice.

Conclusion: The present findings indicate that haploinsufficiency for the intellectual disability- and PTHS-linked transcription factor TCF4 not only affects embryonic neurodevelopment but impedes neurogenesis in the hippocampus of adult mice. These findings suggest that TCF4 haploinsufficiency may have a negative impact on hippocampal function throughout adulthood by impeding hippocampal neurogenesis.

Keywords: Adult neurogenesis; Enriched environment; Hippocampus; Intellectual disability; PTHS; Tcf4.

Fig. 1

TCF-4 is expressed at all stages of adult neurogenesis. Representative images of TCF-4 and NESTIN a, MCM2 b, DCX c and CALBINDIN d. NESTIN is a marker for aNSCs, MCM2 marks proliferative cells. DCX marks immature neurons and CALBINDIN is a marker for mature granule cell neurons. The triangles mark example cells with co-expression of TCF-4 with the respective marker. Scale bar, 50 µm

Fig. 2

Tcf4 haploinsufficiency leads to proliferation deficits in adult neurogenesis. a Representative images and quantification of the DG volume of control and Tcf4Het mice. Haploinsufficient mice show a reduced volume of the DG in comparison to control mice. Scale bar, 100 µm; n = 4. b Representative images and quantification of BrdU incorporating cells in the DG 3 h after last BrdU injection. Tcf4Het mice have a decreased number of BrdU + cells in DG. Scale bar, 100 µm; n = 6. c Representative images and quantification of the number of aNSCs and their activation. Tcf4Het animals show a strong trend towards lower number of NESTIN + cells. The activation ratio is unaltered. Scale bar, 50 µm; n = 6. Data are presented as mean ± SEM

Fig. 3

Tcf4 haploinsufficiency impairs neuronal survival, differentiation and maturation in adult neurogenesis. a Representative images and quantification of BrdU incorporating cells in the DG four weeks after last BrdU injection. Tcf4Het mice have a decreased number of BrdU + cells in DG. Scale bar, 100 µm; n = 9 and 5. b Quantification of the percentage of surviving cells normalized to number of cells that were generated four weeks before. c Representative images and quantification of the number of BrdU + single, BrdU + DCX + PROX1 + triple and BrdU + PROX1 + double positive cells four weeks after last BrdU injection. PROX1 labels granule neurons and DCX immature neurons. The number of immature neurons (BrdU + DCX + PROX1 + triple positive) is increased in Tcf4Het animals, whereas the number of mature neurons (BrdU + PROX1 + positive) is reduced. Scale bar, 50 µm; n = 9 and 5. Data are presented as mean ± SEM

Fig. 4

Enriched environment ameliorates defects in adult neurogenesis due to Tcf4 haploinsufficiency. a Representative images and quantification of the number of proliferative cells, NESTIN + (aNSCs) and the activation of aNSCs in the DG after five weeks of EE. The number of proliferative cells, aNSCs and the activation ratio of aNSC is unaltered. Scale bar, 50 µm; n = 5. b Representative images and quantification of BrdU incorporating cells in the DG four weeks after last BrdU injection and after five weeks of EE. Tcf4Het EE mice have an increased number of BrdU + cells in DG. Scale bar, 100 µm; n = 5. c Representative images and quantification of the number of BrdU + single, BrdU + DCX + PROX1 + triple and BrdU + PROX1 + double positive cells four weeks after last BrdU injection and after five weeks of EE. The number of immature neurons (BrdU + DCX + PROX1 + triple positive) is decreased in Tcf4Het EE animals, whereas the number of mature neurons (BrdU + PROX1 + positive) is increased. Scale bar, 50 µm; n = 5. Data are presented as mean ± SEM