Autism spectrum disorder (ASD) is genetically heterogeneous with convergent symptomatology, suggesting common dysregulated pathways. We analyzed brain transcriptional changes in five mouse models of Pitt-Hopkins Syndrome (PTHS), a syndromic form of ASD caused by mutations in TCF4 (transcription factor 4, not TCF7L2 / T-Cell Factor 4). Analyses of differentially expressed genes (DEGs) highlighted oligodendrocyte (OL) dysregulation, which we confirmed in two additional mouse models of syndromic ASD ( Pten m3m4/m3m4 and Mecp2 tm1.1Bird ). The PTHS mouse models showed cell-autonomous reductions in OL numbers and myelination, functionally confirming OL transcriptional signatures. Next, we integrated PTHS mouse model DEGs with human idiopathic ASD postmortem brain RNA-seq data, and found significant enrichment of overlapping DEGs and common myelination-associated pathways. Importantly, DEGs from syndromic ASD mouse models, and reduced deconvoluted OL numbers, distinguished human idiopathic ASD cases from controls across three postmortem brain datasets. These results implicate disruptions in OL biology as a cellular mechanism in ASD pathology.

Purpose: This study tested the hypothesis that a patientderived orthotopic xenograft (PDOX) model would recapitulate the common clinical phenomenon of breast cancer-induced skeletal muscle (SkM) fatigue in the absence of muscle wasting. This study additionally sought to identify drivers of this condition to facilitate the development of therapeutic agents for patients with breast cancer experiencing muscle fatigue. Experimental Design: Eight female BC-PDOX-bearing mice were produced via transplantation of tumor tissue from 8 female patients with breast cancer. Individual hind limb muscles from BC-PDOX mice were isolated at euthanasia for RNA-sequencing, gene and protein analyses, and an ex vivo muscle contraction protocol to quantify tumor-induced aberrations in SkM function. Differentially expressed genes (DEG) in the BC-PDOX mice relative to control mice were identified using DESeq2, and multiple bioinformatics platforms were employed to contextualize the DEGs. Results: We found that SkM from BC-PDOX-bearing mice showed greater fatigability than control mice, despite no differences in absolute muscle mass. PPAR, mTOR, IL6, IL1, and several other signaling pathways were implicated in the transcriptional changes observed in the BC-PDOX SkM. Moreover, 3 independent in silico analyses identified PPAR signaling as highly dysregulated in the SkM of both BC-PDOX-bearing mice and human patients with early-stage nonmetastatic breast cancer. Conclusions: Collectively, these data demonstrate that the BC-PDOX model recapitulates the expected breast cancer-induced SkM fatigue and further identify aberrant PPAR signaling as an integral factor in the pathology of this condition.

BackgroundBreast cancer patients report a perception of increased muscle fatigue, which can persist following surgery and standardized therapies. In a clinical experiment, we tested the hypothesis that pathways regulating skeletal muscle fatigue are down‐regulated in skeletal muscle of breast cancer patients and that different muscle gene expression patterns exist between breast tumour subtypes. In a preclinical study, we tested the hypothesis that mammary tumour growth in mice induces skeletal muscle fatigue and that overexpression of the cytokine interleukin‐15 (IL‐15) can attenuate mammary tumour‐induced muscle fatigue.MethodsEarly stage non‐metastatic female breast cancer patients (n = 14) and female non‐cancer patients (n = 6) provided a muscle biopsy of the pectoralis major muscle during mastectomy, lumpectomy, or breast reconstruction surgeries. The breast cancer patients were diagnosed with either luminal (ER+/PR+, n = 6), triple positive (ER+/PR+/Her2/neu+, n = 5), or triple negative (ER−/PR−/Her2/neu−, n = 3) breast tumours and were being treated with curative intent either with neoadjuvant chemotherapy followed by surgery or surgery followed by standard post‐operative therapy. Biopsies were used for RNA‐sequencing to compare the skeletal muscle gene expression patterns between breast cancer patients and non‐cancer patients. The C57BL/6 mouse syngeneic mammary tumour cell line, E0771, was used to induce mammary tumours in immunocompetent mice, and isometric muscle contractile properties and fatigue properties were analysed following 4 weeks of tumour growth.ResultsRNA‐sequencing and subsequent bioinformatics analyses revealed a dysregulation of canonical pathways involved in oxidative phosphorylation, mitochondrial dysfunction, peroxisome proliferator‐activated receptor signalling and activation, and IL‐15 signalling and production. In a preclinical mouse model of breast cancer, the rate of muscle fatigue was greater in mice exposed to mammary tumour growth for 4 weeks, and this greater muscle fatigue was attenuated in transgenic mice that overexpressed the cytokine IL‐15.ConclusionsOur data identify novel genes and pathways dysregulated in the muscles of breast cancer patients with early stage non‐metastatic disease, with particularly aberrant expression among genes that would predispose these patients to greater muscle fatigue. Furthermore, we demonstrate that IL‐15 overexpression can attenuate muscle fatigue associated with mammary tumour growth in a preclinical mouse model of breast cancer. Therefore, we propose that skeletal muscle fatigue is an inherent consequence of breast tumour growth, and this greater fatigue can be targeted therapeutically.

Transcription factor 4 (TCF4, also known as ITF2 or E2-2) is a type I basic helix-loop-helix transcription factor. Autosomal dominant mutations in TCF4 cause Pitt-Hopkins syndrome (PTHS), a rare syndromic form of autism spectrum disorder. In this review, we provide an update on the progress regarding our understanding of TCF4 function at the molecular, cellular, physiological, and behavioral levels with a focus on phenotypes and therapeutic interventions. We examine upstream and downstream regulatory networks associated with TCF4 and discuss a range of in vitro and in vivo data with the aim of understanding emerging TCF4-specific mechanisms relevant for disease pathophysiology. In conclusion, we provide comments about exciting future avenues of research that may provide insights into potential new therapeutic targets for PTHS.

Pitt–Hopkins syndrome is an autism spectrum disorder caused by autosomal dominant mutations in the human transcription factor 4 gene (TCF4). One pathobiological process caused by murine Tcf4 mutation is a cell autonomous reduction in oligodendrocytes and myelination. In this study, we show that the promyelinating compounds, clemastine, sobetirome and Sob-AM2 are effective at restoring myelination defects in a Pitt–Hopkins syndrome mouse model. In vitro, clemastine treatment reduced excess oligodendrocyte precursor cells and normalized oligodendrocyte density. In vivo, 2-week intraperitoneal administration of clemastine also normalized oligodendrocyte precursor cell and oligodendrocyte density in the cortex of Tcf4 mutant mice and appeared to increase the number of axons undergoing myelination, as EM imaging of the corpus callosum showed a significant increase in the proportion of uncompacted myelin and an overall reduction in the g-ratio. Importantly, this treatment paradigm resulted in functional rescue by improving electrophysiology and behaviour. To confirm behavioural rescue was achieved via enhancing myelination, we show that treatment with the thyroid hormone receptor agonist sobetirome or its brain penetrating prodrug Sob-AM2, was also effective at normalizing oligodendrocyte precursor cell and oligodendrocyte densities and behaviour in the Pitt–Hopkins syndrome mouse model. Together, these results provide preclinical evidence that promyelinating therapies may be beneficial in Pitt–Hopkins syndrome and potentially other neurodevelopmental disorders characterized by dysmyelination.