Abstract
Pathogenic germline mutations in PIGV lead to glycosylphosphatidylinositol biosynthesis deficiency (GPIBD). Individuals with pathogenic biallelic mutations in genes of the glycosylphosphatidylinositol (GPI) anchor pathway show cognitive impairments, a motor delay and in many cases epilepsy. Thus far, the pathophysiology underlying the disease remains unclear and suitable rodent models that mirror human pathophysiology have not been available. We therefore generated a mouse model using CRISPR-Cas9 to introduce the most prevalent hypomorphic missense mutation in European patients, at a site that is also conserved in mice, Pigv:c.1022C>A (p.A341E). Reflecting the human pathology mutant Pigv341E mice showed deficits in motor coordination and cognitive impairment with poorer long-term spatial memory than wild-type mice, as well as alterations in sociability and sleep patterns. Furthermore, immunohistochemistry showed decreased synaptophysin-immunoreactivity and electrophysiology recordings demonstrated reduced hippocampal synaptic transmission in Pigv341E mice that may underlie impaired memory formation. In single-cell RNA sequencing, Pigv341E-hippocampal cells exhibited changes in gene expression, most prominently in a subtype of microglia and subicular neurons. A significant reduction of Abl1 transcripts in several cell clusters suggests a link to the signaling pathway of GPI-anchored ephrins. We also observed increased levels of Hdc that might affect histamine metabolism with consequences in circadian rhythm. This new mouse model will not only open the doors for further investigation into the pathophysiology of GPIBD in future studies, but will also deepen our understanding in the role of GPI anchor related pathways in brain development.
Significance statement Inherited GPI-anchor biosynthesis deficiencies (IGD) explain a significant number of cases with syndromic intellectual disability. Even though diagnostic approaches are increasing, the pathophysiology underlying the disease remains unclear. Furthermore, suitable rodent models in order to characterize cognitive and social abilities are lacking. Therefore, we generated the first viable mouse model for GPI anchor deficiency with a behavior phenotype that mirrors the patients condition in many aspects. Moreover, we were able to demonstrate novel neurological insights in the mouse model that will facilitate the understanding of the pathophysiology of IGDs in the future.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
We performed flow cytometry on additional clones of CRISPR-engineered mouse embryonic stem (mES) cells to compare the impact of our hypomorphic PIGV mutation to null and wildtype genotypes: mES clones with homozygous hypomorphic mutations in PIGV and PGAP3 revealed a residual surface expression of GPI linked markers. In contrast, homozygous knock out mES clone showed a surface expression of GPI linked markers that was close to 0. In addition, we carried out histologic analysis in the cerebellum and did not observe significant morphological changes in Pigv341E mutant mice. In synopsis with our findings in the hippocampus this suggests that electrophysiology recordings are a suitable assay for studying milder GPIBDs which are due to hypomorphic mutations.
https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE147722