Sex bias in social deficits, neural circuits and nutrient demand in Cttnbp2 autism models

Signaling in autism: Relevance to nutrients and sex

Autism spectrum disorders (ASD) are substantially heterogeneous neuropsychiatric conditions with over a thousand associated genetic factors and various environmental influences, such as infection and nutrition. Additionally, males are four times more likely than females to be affected. This heterogeneity underscores the need to uncover common molecular features within ASD. Recent studies have revealed interactions among genetic predispositions, environmental factors, and sex that may be critical to ASD etiology. This review focuses on emerging evidence for the impact of nutrients-particularly zinc and amino acids-on ASD, as demonstrated in mouse models and human studies. These nutrients have been shown to influence synaptic signaling, dendritic spine formation, and behaviors linked to autism. Furthermore, sex-based differences in nutritional requirements, especially for zinc and amino acids, may contribute to the observed male bias in autism, indicating that interactions between nutrients and genetic factors could be integral to understanding and potentially mitigating ASD symptoms.

mTOR signaling pathway as a pathophysiologic mechanism in preclinical models of autism spectrum disorder

Autism spectrum disorder (ASD) is a highly prevalent multifactorial disorder characterized by social deficits and stereotypies. Despite extensive research efforts, the etiology of ASD remains poorly understood. However, studies using preclinical models have identified the mechanistic target of rapamycin kinase (mTOR) signaling pathway as a key player in ASD-related features. This review examines genetic and environmental models of ASD, focusing on their association with the mTOR pathway. We organize findings on alterations within this pathway, providing insights about the potential mechanisms involved in the onset and maintenance of ASD symptoms. Our analysis highlights the central role of mTOR hyperactivation in disrupting autophagic processes, neural organization, and neurotransmitter pathways, which collectively contribute to ASD phenotypes. The review also discusses the therapeutic potential of mTOR pathway inhibitors, such as rapamycin, in mitigating ASD characteristics. These insights underscore the importance of the mTOR pathway as a target for future research and therapeutic intervention in ASD. This review innovates by bringing the convergence of disrupted mTOR signaling in preclinical models and clinical data associated with ASD.

Vcp overexpression and leucine supplementation extend lifespan and ameliorate neuromuscular junction phenotypes of a SOD1G93A-ALS mouse model

Many genes with distinct molecular functions have been linked to genetically heterogeneous amyotrophic lateral sclerosis (ALS), including SuperOxide Dismutase 1 (SOD1) and Valosin-Containing Protein (VCP). SOD1 converts superoxide to oxygen and hydrogen peroxide. VCP acts as a chaperon to regulate protein degradation and synthesis and various other cellular responses. Although the functions of these two genes differ, in the current report we show that overexpression of wild-type VCP in mice enhances lifespan and maintains the size of neuromuscular junctions (NMJs) of both male and female SOD1G93A mice, a well-known ALS mouse model. Although VCP exerts multiple functions, its regulation of ER formation and consequent protein synthesis has been shown to play the most important role in controlling dendritic spine formation and social and memory behaviors. Given that SOD1 mutation results in protein accumulation and aggregation, it may direct VCP to the protein degradation pathway, thereby impairing protein synthesis. Since we previously showed that the protein synthesis defects caused by Vcp deficiency can be improved by leucine supplementation, to confirm the role of the VCP-protein synthesis pathway in SOD1-linked ALS, we applied leucine supplementation to SOD1G93A mice and, similar to Vcp overexpression, we found that it extends SOD1G93A mouse lifespan. In addition, the phenotypes of reduced muscle strength and fewer NMJs of SOD1G93A mice are also improved by leucine supplementation. These results support the existence of crosstalk between SOD1 and VCP and suggest a critical role for protein synthesis in ASL. Our study also implies a potential therapeutic treatment for ALS.

Autism-related KLHL17 and SYNPO act in concert to control activity-dependent dendritic spine enlargement and the spine apparatus

Dendritic spines, the tiny and actin-rich protrusions emerging from dendrites, are the subcellular locations of excitatory synapses in the mammalian brain that control synaptic activity and plasticity. Dendritic spines contain a specialized form of endoplasmic reticulum (ER), i.e., the spine apparatus, required for local calcium signaling and that is involved in regulating dendritic spine enlargement and synaptic plasticity. Many autism-linked genes have been shown to play critical roles in synaptic formation and plasticity. Among them, KLHL17 is known to control dendritic spine enlargement during development. As a brain-specific disease-associated gene, KLHL17 is expected to play a critical role in the brain, but it has not yet been well characterized. In this study, we report that KLHL17 expression in mice is strongly regulated by neuronal activity and KLHL17 modulates the synaptic distribution of synaptopodin (SYNPO), a marker of the spine apparatus. Both KLHL17 and SYNPO are F-actin-binding proteins linked to autism. SYNPO is known to maintain the structure of the spine apparatus in mature spines and contributes to synaptic plasticity. Our super-resolution imaging using expansion microscopy demonstrates that SYNPO is indeed embedded into the ER network of dendritic spines and that KLHL17 is closely adjacent to the ER/SYNPO complex. Using mouse genetic models, we further show that Klhl17 haploinsufficiency and knockout result in fewer dendritic spines containing ER clusters and an alteration of calcium events at dendritic spines. Accordingly, activity-dependent dendritic spine enlargement and neuronal activation (reflected by extracellular signal-regulated kinase (ERK) phosphorylation and C-FOS expression) are impaired. In addition, we show that the effect of disrupting the KLHL17 and SYNPO association is similar to the results of Klhl17 haploinsufficiency and knockout, further strengthening the evidence that KLHL17 and SYNPO act together to regulate synaptic plasticity. In conclusion, our findings unravel a role for KLHL17 in controlling synaptic plasticity via its regulation of SYNPO and synaptic ER clustering and imply that impaired synaptic plasticity contributes to the etiology of KLHL17-related disorders.