Distinct behavioral profiles across autism spectrum in four mouse models
We examined the behavioral profiles of Fmr1 and Shank3 KO mice, modeling Fragile X and Phelan-McDermid syndromes, respectively, along with Oprm1 KO and chronically isolated mice (Figs. 1, S2-S3, Table S3), all previously published as mouse models of ASD and neurodevelopmental conditions [56, 69–71]. To capture a comprehensive view of their social responses, we exposed these models to distinct social interactions: one involving a family member (e.g. a cage mate, "SI mate") and the other with an unknown conspecific ("SI unknown"), mimicking the daily life of individuals with autism. Additionally, we included a non-social interaction condition with an object ("NSI object"), as control.
In the open field, none of the models exhibited altered behavior following SI mate or NSI object (Table S3). Fmr1 KO mice demonstrated robust social impairments, indicated by a decrease in both total time and mean duration engaged in nose contacts with an unknown mouse both in the reciprocal and three-chambered tests (Fig. 1A, D). This impairment was also observed in heterozygous females in the sociability phase of the three-chambered test (Figure S2A-C). In contrast, Shank3 KO mice displayed impaired social novelty, evident in their lack of preference for a new mouse over a familiar one (Fig. 1B). Surprisingly, Oprm1 KO and isolated mice did not exhibit the expected social impairments as reported previously [69, 71]. Under standard conditions, Oprm1 KO mice only displayed a lack of mate preference in the three-chambered test (Fig. 1C). Elevating light intensity from 15 to 40 lux to strengthen anxious-like behavior revealed social interaction impairments with an unknown animal in Oprm1 KO mice, as evidenced by a reduction in the time spent in nose contact during both the sociability and social novelty phase of the three-chambered tests, as opposed to WT mice tested in dim light conditions (Figure S2D-F). This finding suggests a potential manifestation of induced social impairments or social anxiety — a phenotype situated at the periphery of the autism spectrum.
Regarding stereotyped behaviors, Shank3 KO mice spent more time in self-grooming, accompanied by an increased number of head shakes and a decrease in the time spent digging and in the number of rearing events compared to WT mice (Figs. 1E-F, S3A-B). Conversely, Oprm1 and Fmr1 KO mice demonstrated a reduction in self-grooming time, while isolated mice exhibited a decreased number of head shakes (Fig. 1E-F). Concerning co-occurring features, none of the models exhibited impaired cognitive flexibility in the Y maze, nor did they show locomotion impairments in the open field (Figure S3C-D). Notably, Shank3 KO mice displayed anxious-like behaviors, spending more time in the periphery of the open field arena compared to WT mice (Figure S3E).
In summary, the four models presented distinct behavioral features, with Fmr1 and Shank3 KO mice displaying the most severe phenotypes along the autism spectrum.
Identification of specific molecular markers of social interactions in WT mice
Given that molecular markers for social interactions remain unknown, our primary objective was to identify them, starting with WT mice. We focused on two mRNA families, recognized as potential markers of autism [8, 23, 42, 72]: the OT family, encompassing Oxt and Avp, and their receptors (Oxtr, Avpr1a, Avpr1b), and IEGs and neurotrophic factors, including Arc, Egr1, Fos, Fosb, Jun, Homer1a, Foxp1, Gdnf and Bdnf. We investigated their kinetic profiles up to 6 hours after SI mate, SI unknown, and NSI object, as well as 6 hours following acute social isolation, a condition with negative social valence. We studied their profiles across five key structures within the social circuit: the paraventricular (PVN) and supraoptic nuclei (SON) of the hypothalamus, the caudate putamen (CPU) and nucleus accumbens (NAC) of the striatum, and the medial prefrontal cortex (PFC). To ensure the specificity of our findings, we ruled out circadian or sex biases within the two mRNA families (Figure S4A, Table S4). Notably, none of these mRNAs displayed distinct patterns within a 6-hour period or between males and females, except for Foxp1, which exhibited sexually dimorphic expression in the SON. Interestingly, Arc in the SON was the only mRNAs down-regulated by acute social isolation from cage mates (Figure S4B).
Markers were selected based on significant differences observed between one SI and NSI object, between SI unknown and SI mate, as well as differences between time points exclusively for one SI (Figures S5-S7). We applied a minimum criterion of significance, requiring differences to be present in at least two different brain structures. Consequently, we identified key markers, specifically Avp, Avpr1a, Oxt and Oxtr mRNAs within the OT family, along with Arc, Egr1, Fos, Foxp1 and Homer1a within the IEG family. Notably, SI unknown at 45 minutes emerged as the most distinct stimulus with a rapid and transient increase of mRNAs at 45 minutes, such as Oxtr expression in the NAC and CPU and Egr1, and Homer1a in the PVN and SON (Figs. 2, S5-S7, Table S4). In contrast, SI mate induced sustained regulations, like Avp and Oxt mRNAs in the PVN and SON. Overall, no single structure or mRNA distinctly stood out for a particular social stimulus (Fig. 2). Remarkably, our dataset revealed robust correlations between mRNAs, such as a 0.92 positive correlation between Oxt and Avp (Figure S8A-B). Noteworthy, Foxp1, Homer1a and Egr1 displayed a negative correlation with Oxt and Avp (Figure S8C), suggesting a potential interplay between them.
In summary, we identified Arc, Avp, Avpr1a, Egr1, Fos, Foxp1, Homer1a, Oxt and Oxtr as specific molecular markers of social interactions in WT mice. These markers were selected to assess their levels in the four mouse models, both under basal conditions and following SI unknown at 45 minutes — the most discriminant interaction and time point.
Distinct dysregulations within the oxytocin family among mouse models
Previous studies have proposed OT, AVP, or their receptors as potential common biomarkers of autism [8, 23, 72]. To explore shared dysregulations within the OT family, using Oprm1, Fmr1, Shank3 KO and isolated mice, we assessed alterations in Oxt, Avp, Oxtr and Avpr1a expression following SI unknown at 45 minutes and under basal conditions (Figs. 3, S9-S10, Table S5). In the CPU, Avp was not induced across all four mouse models, as well as Oxtr in three models, compared to WT animals (Fig. 3A). Additionally, we identified two shared dysregulations between two models — Avpr1a in the SON and Oxt in the NAC (Figures S9-S10). However, the majority of dysregulations were rather specific for each mouse model. Fmr1 KO mice displayed a global decrease in the expression of all four mRNAs in the PVN, along with Avp, Oxt, Oxtr in the NAC, and Oxt and Avpr1a in the SON (Figs. 3B, S9-S10). In contrast, isolated mice exhibited an overall increase in Avp, Oxt and Oxtr expression in the PFC (Fig. 3C). Shank3 KO mice did not show additional dysregulations, while in the CPU, Oxt and Avpr1a were also down-regulated in Oprm1 KO mice (Figure S9).
To explore the potential for shared dysregulations beyond the initial OT family, we extended our assessment to include Cd38, involved in OT secretion, and Avpr1b, along with generalist enzymes involved in peptide biosynthesis (Pcsk1, Pcsk2, Pcsk5 and Cpe) and degradation (Lnpep, Ctsa and Rnpep; Figure S11, Table S5). Strikingly, only three shared dysregulations — Cpe, Ctsa, Rnpep in the NAC — were observed among two models (Figure S11). Once again, the majority of dysregulations demonstrated model specificity. In addition to the shared dysregulations, Fmr1 KO mice exhibited 6 unique down-regulations, particularly in the NAC and PVN. Isolated mice displayed mostly up-regulations in the PVN and PFC, along with up- and down-regulations in other structures. Shank3 KO mice showed a down-regulation of Cd38 in the NAC and PFC. Notably, none of these mRNAs were affected in Oprm1 KO mice. To identify the most discriminant mRNAs for model stratification, we applied stringent criteria, requiring a minimum of 6 total and 4 unique dysregulations across three structures and three models. Within the OT family, only Oxt, Avp and Oxtr met these criteria, spanning four structures and four models (Figures S9-S11).
In conclusion, Oxt, Avp and Oxtr emerge as the most discriminant markers within the OT family among the four models. These findings highlight their potential utility in stratifying autism mouse models based on their unique molecular signatures, rather than revealing shared mechanisms.
Widespread dysregulations in social plasticity across mouse models
Akin to the OT family, we investigated dysregulations in social plasticity by testing Arc, Egr1, Fos, Foxp1 and Homer1a — markers identified in WT mice — across the four models following SI unknown at 45 minutes and under basal conditions. Our results revealed extensive dysregulations in IEGs across all five structures and mouse models (Figs. 4, S12-S13, Table S5). We identified 6 shared dysregulations in all four models (SON: Fos, Foxp1 and Homer1a; PVN, Egr1 and Homer1a; CPU: Foxp1), as well as 4 additional dysregulations in three models (SON: Egr1; PFC: Homer1a; NAC: Fos; CPU: Homer1a). However, the underlying causes of these dysregulations varied among the mouse models. In the PVN and SON, IEGs remained at basal levels following SI unknown in Oprm1 KO mice, while in the other models, IEGs were already induced under basal conditions compared to WT mice. Conversely, in the CPU and PFC, the opposite trend was observed. Applying the same criteria as the OT family, we identified Egr1, Fos, Foxp1 and Homer1a, with Homer1a standing out with 16 total and 7 unique dysregulations across all five structures and all four models. Surprisingly, in contrast to the findings in WT animals, Arc was only dysregulated in the PFC of Shank3 KO mice (Figure S12).
In conclusion, our study unveils widespread defects in social plasticity across the models. Egr1, Fos, Foxp1 and Homer1a emerge as the most dysregulated IEGs in the four mouse models, providing valuable markers for model stratification.
Molecular stratification of mouse models using Egr1, Foxp1, Homer1a, Oxt and Oxtr
Integration of qPCR data in the four ASD mouse models following SI unknown aimed to verify connections between our mRNA candidates and specific behavioral parameters (Figure S14). Component 1 of this analysis unveiled a positive association (SON: Foxp1) and negative associations (CPU and PFC: Fos and Homer1a; PFC: Foxp1) with the time spent and mean duration of nose contacts (Figure S14A). These associations were primarily driven by isolated mice, aligning with the observed increase in nose contacts within this specific cohort (Figure S14C). Conversely, positive associations were found between Fos and Homer1a in the PFC and Fos in the CPU, with the number of rearing events and Oprm1 KO mice, indicating a potential opposition between spatial exploration and social interaction. Additionally, grooming behavior was associated with Shank3 KO mice, thus validating our analysis (Figure S14B). This association showed a positive correlation with Homer1a in the PVN and a negative correlation with Oxtr in the PFC. All together, these findings confirm the roles of Fos, Foxp1, Homer1a and Oxtr as molecular markers linked to core autism-like features in mice.
In the last analysis, we crossed data from WT mice and the four mouse models, identifying Egr1, Foxp1, Homer1a, Oxt and Oxtr, as the most dysregulated molecular markers. Avp was excluded due to its high correlation with Oxt that could bias the model towards their shared dysregulations. Employing these five robust molecular markers, we conducted a proof-of-concept for potential stratification among the four mouse models (Fig. 5). The linear discriminant analysis (LDA) integrated molecular data from these markers across the five brain structures in the four models under basal conditions and following SI unknown (Fig. 5A-B). The analysis unveiled distinct classifications, identifying Oprm1 KO (LD1) and isolated mice (LD2) as different models. Although Shank3 and Fmr1 KO mice clustered together, they exhibited individual characteristics (LD3). Among the markers, levels of Oxt (LD1-3) and Homer1a in the CPU (LD1), as well as Homer1a in the NAC (LD2-3) and SON (LD1) exerted the most significant influence on the stratification, followed by Oxtr across the structures.
To challenge our stratification, we tested Arc KO mice, previously documented to manifest social interaction impairments [58, 73]. Based on the five markers, LDA predicted that Arc KO mice would be the closest to Fmr1 KO mice, followed by Shank3 KO mice (Fig. 5A). Indeed, Arc KO mice displayed an intermediate phenotype, showing social interaction impairments coupled with increased self-grooming (Figure S15). Both molecular and behavioral data confirmed Arc KO mice as a valid mouse model with ASD features. Additionally, we employed our stratification to predict the potential responsiveness of subgroups (e.g., Fmr1 and Shank3 KO mice) to treatment administration (Fig. 5C). Solely considering the Oxt and Oxtr markers, we pinpointed cluster 1, consisting of Fmr1 KO and Shank3 KO mice with low levels of Oxt and Oxtr, suggesting a potential positive response to oxytocin treatment in this subgroup.
In conclusion, this study showed the first successful proof-of-concept for the stratification of four mouse models using five molecular markers, providing a potential framework for stratification of individuals with autism.