Reduced BDNF Expression in Auditory Cortex Contributed to Neonatal Pain Induced Hearing Impairment and Dendritic Pruning Deficiency in Mice

Hearing loss in children is common especially in NICU with consequences of worse outcomes in speech, language, education, social functioning, cognitive abilities, and quality of life. Whether neonatal pain is link to increase risks for hearing loss remains to be explored. Here, we implemented Complete Freund's adjuvant (CFA) plantar injection and needle prick model to mimic neonatal pain in NICU during critical period of hearing development. Auditory brainstem response (ABR) test was used to determine the hearing threshold at 4w and 8w postnatal. Sufentanil and Oxycodone were used as analgesic to treat neonatal pain. Hair cell and ribbon synapse stanning were performed to detect cochlear function. Golgi-cox staining and BDNF immunofluorescence of auditory cortex were performed to determine dendritic spine pruning in auditory cortex. The dendritic pruning related protein CaMKII and Rac1/2 level were detected by western blot. We found that CFA induced neonatal pain and ABR threshold increased at 4w and 8w postnatal and the impairment were attenuated after analgesic administration. Neither the inner hair cell (IHC) nor the synapse of CFA mice was damaged in cochlear. CFA mice showed increased dendritic spine density at auditory cortex and reduced BDNF level. Furthermore, Rac1/2 and CaMKII might contributed to the disrupt dendritic spine pruning. Our study suggested that neonatal pain could induced hearing impairment in adulthood ascribed to the reduced BDNF level and AC dendritic spine pruning deficiency, optimal analgesic in early-life could beneficial for hearing development.

Impaired α-tubulin re-tyrosination leads to synaptic dysfunction and is a feature of Alzheimer's disease

In neurons, dynamic microtubules play regulatory roles in neurotransmission and synaptic plasticity. While stable microtubules contain detyrosinated tubulin, dynamic microtubules are composed of tyrosinated tubulin, suggesting that the tubulin tyrosination/detyrosination (Tyr/deTyr) cycle modulates microtubule dynamics and synaptic function. In the Tyr/deTyr cycle, the C-terminal tyrosine of alpha-tubulin is re-added by tubulin-tyrosine-ligase (TTL). Here we show that TTL+/- mice exhibit decreased tyrosinated microtubules, synaptic plasticity and memory deficits, and that reduced TTL expression is a feature of sporadic and familial Alzheimer's disease (AD), with human APPV717I neurons having less dynamic microtubules. We find that spines visited by dynamic microtubules are more resistant to Abeta1-42 and that TTL, by promoting microtubule entry into spines, prevents Abeta1-42-induced spine pruning. Our results demonstrate that the Tyr/deTyr cycle regulates synaptic plasticity, is protective against spine injury, and that tubulin re-tyrosination is lost in AD, providing evidence that a defective Tyr/deTyr cycle may contribute to neurodegeneration.

Semaphorin3F Drives Dendritic Spine Pruning through Rho-GTPase Signaling

Dendritic spines of cortical pyramidal neurons are initially overproduced then remodeled substantially in the adolescent brain to achieve appropriate excitatory balance in mature circuits. Here we investigated the molecular mechanism of developmental spine pruning by Semaphorin 3F (Sema3F) and its holoreceptor complex, which consists of immunoglobulin-class adhesion molecule NrCAM, Neuropilin-2 (Npn2), and PlexinA3 (PlexA3) signaling subunits. Structure-function studies of the NrCAM-Npn2 interface showed that NrCAM stabilizes binding between Npn2 and PlexA3 necessary for Sema3F-induced spine pruning. Using a mouse neuronal culture system, we identified a dual signaling pathway for Sema3F-induced pruning, which involves activation of Tiam1-Rac1-PAK1-3 -LIMK1/2-Cofilin1 and RhoA-ROCK1/2-Myosin II in dendritic spines. Inhibitors of actin remodeling impaired spine collapse in the cortical neurons. Elucidation of these pathways expands our understanding of critical events that sculpt neuronal networks and may provide insight into how interruptions to these pathways could lead to spine dysgenesis in diseases such as autism, bipolar disorder, and schizophrenia.

Sex and Pubertal Status Influence Dendritic Spine Density on Frontal Corticostriatal Projection Neurons in Mice

In humans, nonhuman primates, and rodents, the frontal cortices exhibit grey matter thinning and dendritic spine pruning that extends into adolescence. This maturation is believed to support higher cognition but may also confer psychiatric vulnerability during adolescence. Currently, little is known about how specific cell types in the frontal cortex mature or whether puberty plays a role in the maturation of some cell types but not others. Here, we used mice to characterize the spatial topography and adolescent development of cross-corticostriatal (cSTR) neurons that project through the corpus collosum to the dorsomedial striatum. We found that apical spine density on cSTR neurons in the medial prefrontal cortex decreased significantly between late juvenile (P29) and young adult time points (P60), with females exhibiting higher spine density than males at both ages. Adult males castrated prior to puberty onset had higher spine density compared to sham controls. Adult females ovariectomized before puberty onset showed greater variance in spine density measures on cSTR cells compared to controls, but their mean spine density did not significantly differ from sham controls. Our findings reveal that these cSTR neurons, a subtype of the broader class of intratelencephalic-type neurons, exhibit significant sex differences and suggest that spine pruning on cSTR neurons is regulated by puberty in male mice.

Sex and pubertal status influence dendritic spine density onto frontal corticostriatal projection neurons

In humans, nonhuman primates, and rodents, the frontal cortices exhibit grey matter thinning and dendritic spine pruning that extends late into adolescence. This protracted maturation is believed to support higher cognition but may also confer psychiatric vulnerability during adolescence. Currently, little is known about how different cell types in the frontal cortex mature or whether puberty plays a role. Here, we used mice to characterize the spatial topography and adolescent development of cross-corticostriatal (cSTR) neurons that project to the dorsomedial striatum (DMS). We found that apical spine density on cSTR neurons in the medial prefrontal cortex decreased significantly between late juvenile (P29) and young adult time points (P60), with females exhibiting higher spine density than males at both ages. Adult males castrated prior to puberty onset had higher spine density compared to sham controls. Adult females ovariectomized before puberty onset showed greater variance in spine density measures on cSTR cells compared to controls, but their mean spine density did not significantly differ from sham controls. Our findings reveal that these cSTR neurons, a subtype of the broader class of intratelencephalic-type neurons, exhibit significant sex differences and suggest that spine pruning on cSTR neurons is regulated by puberty in males.

CRMP2 mediates Sema3F-dependent axon pruning and dendritic spine remodeling

ABSTRACTRegulation of axon guidance and pruning of inappropriate synapses by class 3 semaphorins is key to development of neural circuits. Collapsin response mediator protein 2 (CRMP2) has been shown to regulate axon guidance by mediating Semaphorin 3A (Sema3A) signaling and its dysfunction has been linked to schizophrenia, however, nothing is known about its role in the synapse pruning. Here, using newly generated crmp2−/− mice we demonstrate that while CRMP2 has only a moderate effect on Sema3A-dependent axon guidance in vivo, it is essential for Sema3F-dependent axon pruning and dendritic spine remodeling. We first demonstrate that CRMP2 deficiency interferes with Sema3A signaling in compartmentalized neuron cultures and leads to a mild defect in axon guidance in peripheral nerves and corpus callosum. Strikingly, we show that crmp2−/− mice display more prominent defects in dendritic spine pruning and stereotyped axon pruning in hippocampus and visual cortex consistent with impaired Sema3F signaling and with autism spectrum disorder (ASD)-rather than schizophrenia-like phenotype. Indeed, we demonstrate that CRMP2 mediates Sema3F-induced axon retraction in primary neurons and that crmp2−/− mice display early postnatal behavioral changes linked to ASD. In conclusion, we demonstrate that CRMP2 is an essential mediator of Sema3F-dependent synapse pruning and its dysfunction in early postnatal stages shares histological and behavioral features of ASD.