Authors :
Presenting Author: Ria Parikh, BA, BS – University of Maryland School of Medicine
Asmaa Hijazi, BS – University of Maryland School of Medicine
ThachVu Nguyen, BS – University of Maryland School of Medicine
Irina Sbornova, BS – University of Maryland School of Medicine
Janice Babus, BS – University of Maryland School of Medicine
Philip Iffland, PhD – University of Maryland Baltimore
Peter Crino, MD, PhD – University of Maryland School of Medicine
Whitney Parker, MD, PhD – University of Maryland School of Medicine
Rationale:
Polyhydramnios, Megalencephaly, and Symptomatic Epilepsy (PMSE) syndrome and KPTN-related Disorder (KRD) are autosomal recessive neurodevelopmental disorders characterized by epilepsy, developmental delay, and an enlarged brain size (megalencephaly). PMSE and KRD are caused by pathogenic variants in STRADA and KPTN, respectively, that encode proteins upstream of the mechanistic target of rapamycin complex 1 (mTORC1). STRADA is a pseudokinase that activates liver kinase B1 (LKB1) in response to low cellular energy levels, and KPTN is part of the KICSTOR complex that modulates mTORC1 in response to cellular amino acid levels. Little is known about the role of these proteins in cortical development and how their loss promotes seizure onset. Preliminary data in our labs suggest that the loss of STRADA or KPTN may contribute to epilepsy by disrupting the development of cortical interneurons (cINs), leading to altered numbers and lamination in the cortex.
Methods:
The expression and lamination of cINs was investigated in adult Strada and Kptn knockout (KO), heterozygous (Het) and wildtype (WT) mice (C57BL/6, age P21-P30, n=4-5) and in human PMSE (female, age 7 months) brain using immunohistochemistry in formalin-fixed, paraffin embedded (FFPE) tissue. We assessed overall interneuron (IN) numbers labeled with GABA, and IN subtypes, including parvalbumin (PV), somatostatin (SST), and serotonin receptor 3a (5HT3aR) in the motor cortex, somatosensory cortex, hippocampus, reticular thalamus, and striatum. IN numbers were assessed using fluorescence microscopy and quantified using ImageJ (one-way ANOVA with Tukey’s multiple comparisons). In the human PMSE tissue, we analyzed IN numbers in frontal cortex, hippocampus, basal ganglia, and thalamus samples, and these samples were compared to age-matched and adult formalin-fixed control tissue samples.
Results:
There were differentially altered numbers of cortical GABAergic cINs, specifically parvalbumin-positive (PV+) cINs, in STRADA KO versus KPTN KO mice. Strada KO mice showed reduced numbers of GABAergic (p=.014), and specifically PV+ (p=.048) cINs in the somatosensory cortex compared to WT, while Kptn KO mice showed an increase in overall cIN and PV+ (p=.003) neurons in the somatosensory cortex across all cortical layers compared to WT. We also found reduced numbers of GABAergic cINs, labeled with GAD67, in human PMSE frontal cortex, compared to both age-matched and adult unaffected cortex.
Conclusions:
In the absence of STRADA and KPTN, numbers of GABAergic interneurons, specifically PV+ INs, are altered in the somatosensory and frontal cortices, suggesting potential deficits in the development and maturation of cINs. Further investigation is needed to understand the mechanistic underpinnings of these alterations and ultimately, how a change in inhibitory/excitatory neuron ratio might contribute to epilepsy in these neurodevelopmental disorders.
Funding: University of Maryland Dept. of Neurosurgery Startup Funds to WEP, 5R37NS125632-04 to PBC