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Background A growing body of evidence suggests that immune dysfunction and inflammation in the peripheral tissues as well as the central nervous system are associated with the neurodevelopmental deficits observed in autism spectrum disorder (ASD). Elevated expression of pro-inflammatory cytokines in the plasma, serum, and peripheral blood mononuclear cells of ASD has been reported. These cytokine expression levels are associated with the severity of behavioral impairments and symptoms in ASD. In a prior study, our group reported that tumor necrosis factor-α (TNF-α) expression in granulocyte–macrophage colony-stimulating factor-induced macrophages (GM-CSF MΦ) and the TNF-α expression ratio in GM-CSF MΦ/M-CSF MΦ (macrophage colony-stimulating factor-induced macrophages) was markedly higher in individuals with ASD than in typically developed (TD) individuals. However, the mechanisms of how the macrophages and the highly expressed cytokines affect neurons remain to be addressed. Methods To elucidate the effect of macrophages on human neurons, we used a co-culture system of control human-induced pluripotent stem cell-derived neurons and differentiated macrophages obtained from the peripheral blood mononuclear cells of five TD individuals and five individuals with ASD. All participants were male and ethnically Japanese. Results Our results of co-culture experiments showed that GM-CSF MΦ affect the dendritic outgrowth of neurons through the secretion of pro-inflammatory cytokines, interleukin-1α and TNF-α. Macrophages derived from individuals with ASD exerted more severe effects than those derived from TD individuals. Limitations The main limitations of our study were the small sample size with a gender bias toward males, the use of artificially polarized macrophages, and the inability to directly observe the interaction between neurons and macrophages from the same individuals. Conclusions Our co-culture system revealed the non-cell autonomous adverse effects of GM-CSF MΦ in individuals with ASD on neurons, mediated by interleukin-1α and TNF-α. These results may support the immune dysfunction hypothesis of ASD, providing new insights into its pathology.

Microglia and brain-derived neurotrophic factor (BDNF) are essential for the neuroplasticity that characterizes critical developmental periods. The experience-dependent development of social behaviors—associated with the medial prefrontal cortex (mPFC)—has a critical period during the juvenile period in mice. However, whether microglia and BDNF affect social development remains unclear. Herein, we aimed to elucidate the effects of microglia-derived BDNF on social behaviors and mPFC development. Mice that underwent social isolation during p21–p35 had increased Bdnf in the microglia accompanied by reduced adulthood sociability. Additionally, transgenic mice overexpressing microglial Bdnf —regulated using doxycycline at different time points—underwent behavioral, electrophysiological, and gene expression analyses. In these mice, long-term overexpression of microglial BDNF impaired sociability and excessive mPFC inhibitory neuronal circuit activity. However, administering doxycycline to normalize BDNF from p21 normalized sociability and electrophysiological function in the mPFC, whereas normalizing BDNF from later ages (p45–p50) did not normalize electrophysiological abnormalities in the mPFC, despite the improved sociability. To evaluate the possible role of BDNF in human sociability, we analyzed the relationship between adverse childhood experiences and BDNF expression in human macrophages, a possible proxy for microglia. Results show that adverse childhood experiences positively correlated with BDNF expression in M2 but not M1 macrophages. In summary, our study demonstrated the influence of microglial BDNF on the development of experience-dependent social behaviors in mice, emphasizing its specific impact on the maturation of mPFC function, particularly during the juvenile period. Furthermore, our results propose a translational implication by suggesting a potential link between BDNF secretion from macrophages and childhood experiences in humans.

This study aimed to explore the relationship between self-esteem and tumor necrotic factor-alpha (TNF-α) expression in individuals with autism spectrum disorder (ASD). Self-esteem was assessed using the Contingencies of Self-Worth (CSW) scale, with a focus on external and internal contingencies, and TNF-α expression was measured, given its association with both ASD pathophysiology and self-esteem in prior studies. We enrolled 51 high-functioning individuals with ASD and 34 typically developed (TD) individuals. Self-esteem was assessed using the Japanese version of the CSW scale, which evaluates seven domains, and the Personal Sense of Power. TNF-α expression in plasma was quantified via ELISA. Correlations of CSW scores and the Personal Sense of Power with TNF-α levels were analyzed using multiple regression models adjusted for confounding factors such as age, sex, education level, and autistic symptoms. In ASD individuals, TNF-α expression was significantly negatively correlated with the external CSW domain of others' approval and showed a trend toward negative correlations with appearance and relationship harmony. These correlations were not observed in the TD individuals. Likewise, the Personal Sense of Power within family settings showed a trend toward positive correlations with TNF-α expression in ASD individuals, but not in TD individuals. This study highlights the implication of TNF-α levels in the self-esteem of ASD individuals, particularly in interpersonal relationships. Lower TNF-α expression was associated with higher self-esteem in social contexts, independent of the severity of autistic symptoms. These findings suggest a biological link between inflammatory pathways and self-esteem in ASD, contributing to a deeper understanding of the interplay between immune function and psychological well-being in this population.

A number of studies have indicated that relaxing and pleasant melodies are useful for the treatment of patients with psychiatric disorders, including schizophrenia, depression, and dementia. However, few studies have investigated what constitutive elements of the music had an effect on brain activity. As Canon chord progression is one of critical elements for pleasant melodies, we sought to examine the effects of Canon chord progression and pitch-shifted Canon chord progression on brain activity using performance on the auditory oddball task during event-related potentials (ERPs) in 30 healthy subjects. Unexpectedly, we found no differences in ERP components between subjects listening to Canon chord progression (n=15) or pitch-shifted Canon chord progression (n=15). Next, we divided participants into two groups: those who found the melody pleasant (n=17) and those who did not (n=13), for both Canon chord progression and pitch-shifted Canon chord progression. The average of P300 amplitude was higher at Fz in subjects found the music pleasant versus those finding it unpleasant. Moreover, subjects who found it pleasant exhibited higher motivation scores than those who felt it was unpleasant, whereas listening to Canon chord progression did not matter. These findings suggest that the effects of Canon chord progression on brain activity and motivation depend on subjective feelings, not the chord progression per se.

A number of studies have indicated that relaxing and pleasant melodies are useful for the treatment of patients with psychiatric disorders, including schizophrenia, depression, and dementia. However, few studies have investigated what constitutive elements of the music had an effect on brain activity. As Canon chord progression is one of critical elements for pleasant melodies, we sought to examine the effects of Canon chord progression and pitch-shifted Canon chord progression on brain activity using performance on the auditory oddball task during event-related potentials (ERPs) in 30 healthy subjects. Unexpectedly, we found no differences in ERP components between subjects listening to Canon chord progression (n=15) or pitch-shifted Canon chord progression (n=15). Next, we divided participants into two groups: those who found the melody pleasant (n=17) and those who did not (n=13), for both Canon chord progression and pitch-shifted Canon chord progression. The average of P300 amplitude was higher at Fz in subjects found the music pleasant versus those finding it unpleasant. Moreover, subjects who found it pleasant exhibited higher motivation scores than those who felt it was unpleasant, whereas listening to Canon chord progression did not matter. These findings suggest that the effects of Canon chord progression on brain activity and motivation depend on subjective feelings, not the chord progression per se.