Project Summary
Neurodevelopmental disorders (NDDs) are heterogenous and usually present with complex etiology.
Individuals with these conditions present cognitive impairment accompanied by lifelong deficits; yet remarkably
little is known about their neurological basis. To develop effective treatments, it is imperative to understand the
dysregulation of molecular and cellular processes leading to these conditions. PACS2 syndrome is a NDD
characterized by epilepsy, intellectual disability, craniofacial abnormalities, and hypotonia. PACS2 syndrome
results from a recurrent de novo c.625G>A variant in the gene encoding Phosphofurin Acidic Cluster Sorting
protein 2 (PACS2) resulting in a Glutamate to Lysine (p.E209K) substitution. PACS2 encodes a multifunctional
sorting protein that mediates protein trafficking between the endomembrane system which includes the ER,
Golgi, mitochondria, lysosomes, and the plasma membrane. The mechanism of PACS2 syndrome is relatively
understudied, however, a recent report found that PACS2 p.E209K has an increased half-life compared to WT
PACS2. They also found an increased association of PACS2 p.E209K with 14-3-3e, and that cells
overexpressing PACS2 p.E209K or 14-3-3e undergo apoptosis. Given that PACS2 function has rarely been
studied in neurons or model organisms and the neuronal-specific effect of the p.E209K variant are not known.
Here, we will use patient-derived and CRISPR knock-in induced pluripotent stem cell (iPSC) models to study the
molecular and neuronal-specific deficits associated which PACS2 p.E209K. We hypothesize that neurons
carrying the PACS2 p.E209K substitution present with increased susceptibility to apoptosis via the lysosomal
pathway. We will test this hypothesis by addressing whether PACS2 p.E209K promotes apoptosis, precocious
neural differentiation and hyperexcitability in neurons (aim 1) by increasing PACS2 stability and PACS2-
mediated recruitment of pro-apoptotic proteins to the lysosomes in neurons (aim 2). Results from this proposal
will greatly enhance our understanding of the mechanisms by which PACS2 p.E209K affects developing
neurons. Moreover, we will uncover mechanisms by which PACS2 in general and PACS2 p.E209K in particular,
regulate pro-apoptotic pathways. Finally, results from this proposal will contribute to our knowledge of disease
mechanisms for PACS2 Syndrome, which may reveal therapy targets.