Early 17β-estradiol treatment reduces seizures but not abnormal behaviour in mice with expanded polyalanine tracts in the Aristaless related homeobox gene (ARX)

Arx revisited: involved in the development of GABAergic interneurons

The aristaless-related homeobox (Arx) transcription factor, located on the X chromosome, has been implicated in a wide range of neurological disorders, including intellectual disability and epilepsy, as well as diabetes and pancreatic developmental disorders. In the mouse brain, Arx is expressed not only in the olfactory bulb (OB) and cerebral cortex progenitor cells but also in these gamma-aminobutyric acid (GABA)-releasing interneurons. In the initial study, constitutive Arx knockout (KO) mice showed aberrant migration and a reduction in GABAergic interneurons in the neonatal OB. However, constitutive Arx KO mice with perinatal lethality preclude further analysis in adolescent or adult mice. To overcome this, Arx-floxed mice have been crossed with Cre driver mice to generate conditional KO mice with selective Arx deletion in distinct interneuron progenitors. These studies have identified Arx as a key transcriptional regulator involved in the generation, fate determination, and migration of cortical interneurons. This review focuses on the critical role of Arx in the development of progenitor cells and the migration of interneurons in the mouse OB and cerebral cortex, and discusses differences in Arx mutant-based abnormality between mouse mutants and human patients.

Maternal aging reduces female fecundity and alters offspring phenotype in a sex-specific manner

Context The age of childbearing in women has increased, with more babies born to women over 30years old than to those in their 20s. However, increasing maternal age is associated with a range of pregnancy and perinatal complications, such as reduced chance of conception, and higher risk of miscarriage or fetal death. Further, epidemiological studies indicate that advanced maternal age is also linked to a higher incidence of metabolic and neurodevelopmental disorders in offspring, such as Type 1 diabetes and autism spectrum disorder (ASD). Aims Mature female mice recapitulate many of the fertility characteristics seen in older women, such as reduced egg number and quality, providing a robust experimental model. This study examined fertility and offspring phenotypes in female mice at the onset of reproductive aging. Methods Firstly, fecundity in mice was measured from 3 to 18months of age. Secondly, reproductive outcomes in aged female mice (12months old) were compared to those of young females (3months of age). Growth of the offspring was assessed, as well as metabolism, behaviour, and immune function in adulthood. Key results Female aging reduced pregnancy rate, litter size and pup survival to weaning. Maternal age did not affect adult offspring immune function; however, female offspring had higher body weights, and male littermates presented dysregulated glucose tolerance and hyperactivity. Conclusions Maternal age affects offspring survival and health in a sex-specific manner. Implications These findings expand our understanding of maternal programming of offspring health, particularly the effects of increased age at pregnancy.

Efficacy and tolerability of celastrol and edaravone in the multiple-hit rat model of infantile spasms

OBJECTIVE

To test whether anti-inflammatory and antioxidant drugs that inhibit the nuclear factor kappa light chain enhancer of activated B cells (NF-kB), celastrol and edaravone, suppress spasms and improve developmental outcomes in the multiple-hit rat model of refractory infantile spasms (IS) due to structural lesions.

METHODS

Postnatal day 3 (PN3) Sprague-Dawley rats were treated according to the multiple-hit IS model protocol. Using a randomized, blinded, vehicle-controlled, dose- and time-response study design, we tested the effects of single celastrol [1, 2, or 4 mg/kg intraperitoneally (i.p.), 10-14 rats/group] or edaravone (1, 10 or 30 mg/kg i.p., 14-17 rats/group) injections vs their vehicles on behavioral and electroclinical spasms and developmental milestones. Video-EEG monitoring was done on PN6-7 (n = 11-12 rats/group). Pulse celastrol treatment effects (PN4: 4 mg/kg, PN5-6: 2 mg/kg/day i.p.) were determined on spasms, developmental milestones and Barnes maze. Celastrol and edaravone pharmacokinetics in plasma and neocortex were assessed. Linear mixed model analysis of raw or normalized log-transformed spasm frequencies, considering repeated observations was used.

RESULTS

Single (2-4 mg/kg i.p) or pulse celastrol, but not edaravone, reduced behavioral and electroclinical spasms frequencies within 5hrs. Pulse celastrol did not affect spasm-freedom, survival, developmental milestones or Barnes maze performance. Celastrol had erratic i.p. absorption with maximum concentrations observed between 2-4 h, when effects on spasms were seen. Edaravone had low blood-to-brain permeability.

CONCLUSIONS

Celastrol's efficacy on spasms is partially explained by its better brain penetration than edaravone's. NFkB inhibitors may be useful in treating drug-resistant IS but delivery methods with improved bioavailability and brain permeability are needed.

Dual effects of ARX poly-alanine mutations in human cortical and interneuron development

Infantile spasms, with an incidence of 1.6 to 4.5 per 10,000 live births, are a relentless and devastating childhood epilepsy marked by severe seizures but also leads to lifelong intellectual disability. Alarmingly, up to 5% of males with this condition carry a mutation in the Aristaless-related homeobox ( ARX ) gene. Our current lack of human-specific models for developmental epilepsy, coupled with discrepancies between animal studies and human data, underscores the gap in knowledge and urgent need for innovative human models, organoids being one of the best available. Here, we used human neural organoid models, cortical organoids (CO) and ganglionic eminences organoids (GEO) which mimic cortical and interneuron development respectively, to study the consequences of PAE mutations, one of the most prevalent mutation in ARX . ARX PAE produces a decrease expression of ARX in GEOs, and an enhancement in interneuron migration. That accelerated migration is cell autonomously driven, and it can be rescued by inhibiting CXCR4. We also found that PAE mutations result in an early increase in radial glia cells and intermediate progenitor cells, followed by a subsequent loss of cortical neurons at later timepoints. Moreover, ARX expression is upregulated in COs derived from patients at 30 DIV and is associated with alterations in the expression of CDKN1C . Furthermore, ARX PAE assembloids had hyperactivity which were evident at early stages of development. With effective treatments for infantile spasms and developmental epilepsies still elusive, delving into the role of ARX PAE mutations in human brain organoids represents a pivotal step toward uncovering groundbreaking therapeutic strategies.

Mechanisms of infantile epileptic spasms syndrome: What have we learned from animal models?

The devastating developmental and epileptic encephalopathy of infantile epileptic spasms syndrome (IESS) has numerous causes, including, but not limited to, brain injury, metabolic, and genetic conditions. Given the stereotyped electrophysiologic, age-dependent, and clinical findings, there likely exists one or more final common pathways in the development of IESS. The identity of this final common pathway is unknown, but it may represent a novel therapeutic target for infantile spasms. Previous research on IESS has focused largely on identifying the neuroanatomic substrate using specialized neuroimaging techniques and cerebrospinal fluid analysis in human patients. Over the past three decades, several animal models of IESS were created with an aim to interrogate the underlying pathogenesis of IESS, to identify novel therapeutic targets, and to test various treatments. Each of these models have been successful at recapitulating multiple aspects of the human IESS condition. These animal models have implicated several different molecular pathways in the development of infantile spasms. In this review we outline the progress that has been made thus far using these animal models and discuss future directions to help researchers identify novel treatments for drug-resistant IESS.

Cortical Parvalbumin-Positive Interneuron Development and Function Are Altered in the APC Conditional Knockout Mouse Model of Infantile and Epileptic Spasms Syndrome

Infantile and epileptic spasms syndrome (IESS) is a childhood epilepsy syndrome characterized by infantile or late-onset spasms, abnormal neonatal EEG, and epilepsy. Few treatments exist for IESS, clinical outcomes are poor, and the molecular and circuit-level etiologies of IESS are not well understood. Multiple human IESS risk genes are linked to Wnt/β-catenin signaling, a pathway that controls developmental transcriptional programs and promotes glutamatergic excitation via β-catenin's role as a synaptic scaffold. We previously showed that deleting adenomatous polyposis coli (APC), a component of the β-catenin destruction complex, in excitatory neurons (APC cKO mice, APCfl/fl x CaMKIIαCre) increased β-catenin levels in developing glutamatergic neurons and led to infantile behavioral spasms, abnormal neonatal EEG, and adult epilepsy. Here, we tested the hypothesis that the development of GABAergic interneurons (INs) is disrupted in APC cKO male and female mice. IN dysfunction is implicated in human IESS, is a feature of other rodent models of IESS, and may contribute to the manifestation of spasms and seizures. We found that parvalbumin-positive INs (PV+ INs), an important source of cortical inhibition, were decreased in number, underwent disproportionate developmental apoptosis, and had altered dendrite morphology at P9, the peak of behavioral spasms. PV+ INs received excessive excitatory input, and their intrinsic ability to fire action potentials was reduced at all time points examined (P9, P14, P60). Subsequently, GABAergic transmission onto pyramidal neurons was uniquely altered in the somatosensory cortex of APC cKO mice at all ages, with both decreased IPSC input at P14 and enhanced IPSC input at P9 and P60. These results indicate that inhibitory circuit dysfunction occurs in APC cKOs and, along with known changes in excitation, may contribute to IESS-related phenotypes.SIGNIFICANCE STATEMENT Infantile and epileptic spasms syndrome (IESS) is a devastating epilepsy with limited treatment options and poor clinical outcomes. The molecular, cellular, and circuit disruptions that cause infantile spasms and seizures are largely unknown, but inhibitory GABAergic interneuron dysfunction has been implicated in rodent models of IESS and may contribute to human IESS. Here, we use a rodent model of IESS, the APC cKO mouse, in which β-catenin signaling is increased in excitatory neurons. This results in altered parvalbumin-positive GABAergic interneuron development and GABAergic synaptic dysfunction throughout life, showing that pathology arising in excitatory neurons can initiate long-term interneuron dysfunction. Our findings further implicate GABAergic dysfunction in IESS, even when pathology is initiated in other neuronal types.

A Review of Targeted Therapies for Monogenic Epilepsy Syndromes

Genetic sequencing technologies have led to an increase in the identification and characterization of monogenic epilepsy syndromes. This increase has, in turn, generated strong interest in developing “precision therapies” based on the unique molecular genetics of a given monogenic epilepsy syndrome. These therapies include diets, vitamins, cell-signaling regulators, ion channel modulators, repurposed medications, molecular chaperones, and gene therapies. In this review, we evaluate these therapies from the perspective of their clinical validity and discuss the future of these therapies for individual syndromes.