Seizures in PPT1 Knock-In Mice Are Associated with Inflammatory Activation of Microglia

Abstract

Infantile neuronal ceroid lipofuscinosis (INCL), the most severe form of neuronal ceroid lipofuscinoses, is caused by mutations in the lysosomal enzyme palmitoyl protein thioesterase 1 (PPT1). Typical symptoms of this disease include progressive psychomotor developmental retardation, visual failure, seizures, and premature death. Here, we investigated seizure activity and relevant pathological changes in PPT1 knock-in mice (PPT1 KI). The behavior studies in this study demonstrated that PPT1 KI mice had no significant seizure activity until 7 months of age, and local field potentials also displayed epileptiform activity at the same age. The expression levels of Iba-1 and CD68 demonstrated, by Western blot analysis, the inflammatory cytokine TNF-α content measured with enzyme-linked immunosorbent assay, and the number of microglia demonstrated by immunohistochemistry (IHC) were significantly increased at age of 7 months, all of which indicate microglia activation at an age of seizure onset. The increased expression of GFAP were seen at an earlier age of 4 months, and such an increase reached its peak at age of 6 months, indicating that astrocyte activation precedes microglia. The purinergic P2X7 receptor (P2X7R) is an ATP-sensitive ionic channel that is highly expressed in microglia and is fundamental to microglial activation, proliferation, cytokines release and epilepsy. We show that the ATP concentration in hippocampal tissue in PPT1 KI mice was increased using an enhanced ATP assay kit and demonstrated that the antagonist of P2X7R, A-438079, significantly reduced seizures in PPT1 KI mice. In contrast to glial cell activation and proliferation, a significant reduction in synaptic proteins GABAAR was seen in PPT1 KI mice. These results indicate that seizure in PPT1 KI mice may be associated with microglial activation involved in ATP-sensitive P2X7R signaling and impaired inhibitory neurotransmission.

Reduction of Neuroinflammation and Seizures in a Mouse Model of CLN1 Batten Disease using the Small Molecule Enzyme Mimetic, N-Tert-Butyl Hydroxylamine

“…Further, microglial activation is associated with seizure onset in a CLN1 mouse model [40]. Therefore, one potential interpretation is that NtBuHA treatment suppressed seizures via a reduction in neuroinflammation [40,42,44,48].…”

“…2C). An additional indicator of neuroinflammation in CLN1 that intensifies with disease progression is microglial activation, detectable by the adoption of a pro-inflammatory morphology [39][40][41]. Morphological analysis of ionized calcium-binding adaptor molecule 1 (Iba1)-positive microglia in S1 and V1 revealed that Cln1 -/mice receiving NtBuHA exhibited an increased number of microglial process intersections and elongated average process length compared to untreated controls at both 2 and 6 months (Fig.…”

“…While the presence of gliosis serves as a histopathological correlate of disease progression, it has also been causally implicated in several CLN1 disease processes, including the generation of seizures [45][46][47]. Further, microglial activation is associated with seizure onset in a CLN1 mouse model [40]. Therefore, one potential interpretation is that NtBuHA treatment suppressed seizures via a reduction in neuroinflammation [40,42,44,48].…”

The P2X7 Receptor as a Mechanistic Biomarker for Epilepsy

“…Finally, a recent study analysed the epileptic phenotype in mice transgenic for the lysosomal enzyme palmitoyl protein thioesterase 1 (PPT1). These mice develop epilepsy after 7 months of age, including increased microgliosis [ 99 ]. When treated with P2X7R antagonists, PPI transgenic mice experienced fewer seizures, further supporting the antiepileptogenic potential of P2X7R antagonism.…”

GABAAR-PPT1 palmitoylation homeostasis controls synaptic transmission and circuitry oscillation in CLN1 disease

“…Further, GABA A R plays a central role in synchronising network neuronal activity, which are tightly associated with higher brain functions such as learning and memory(Nakazono et al, 2018). PPT1-KI mice carrying nonsense mutations in the CLN1/PPT1 gene exhibited reduced expression of GABA A R along with impaired gamma oscillation and seizure onset (Zhang et al, 2022). These findings indicate the importance of GABA A R in CLN1 disease.…”