Research Rita Cacace

Abstract

This pilot project proposal is based on our genetic discovery of the involvement of dipeptidyl peptidase 6 (DPP6) loss in dementia (Cacace et al., 2019), which was recently confirmed by an independent group (Pottier et al., 2019). DPP6 is a protein highly expressed in brain, where it regulates the expression and the function of the voltage-gated potassium channel Kv4.2. These channels regulate neuronal excitability. A decrease in potassium currents, due to DPP6 loss, is known to contribute to neuronal hyperexcitability. We hypothesize that in patients with dementia, the loss of DPP6 and Kv4.2, enhances dendritic and neuronal loss and causes neurodegeneration by altering the homeostasis of neuronal firing. As neuronal hyperexcitability is detectable in vivo by using noninvasive imaging techniques (i.e. functional magnetic resonance imaging and magneto-encephalography), and could possibly be farmacomodulated, we will develop two different human derived in vitro systems recapitulating the phenotypes due to DPP6 loss, for compound screenings. The project is designed in three work packages spanning 2 years timeframe. We will use human derived induced pluripotent stem cells (hiPSC) in which we will knock-out (KO) DPP6 and differentiate into neurons and we will measure how the absence of DPP6 affects neuronal morphology and function compared to wild-type cells. Once these read-outs are identified, will be used to test libraries of compounds, searching for drugs able to ameliorate the detected phenotype (WP1). Furthermore, we will generate cerebral organoids to evaluate in a 3D system the effect of DPP6 loss on both neurogenesis and neurodegeneration. We will use this second model to further evaluate the compounds previously selected, to collect functional readouts in a more complex system (WP3). In parallel to these two approaches, we will study the interacting partners of DPP6 in iPSC derived neurons. We will use endogenous DPP6 protein tagging to immunoprecipitate DPP6 and relative partners. With this experiment we aim to identify additional proteins to investigate and, eventually, to target in order to indirectly modulate DPP6 or DPP6-Kv4.2 function (WP2). Collecting sufficient functional evidences on how DPP6 loss impairs neuronal excitability in human derived neuronal models, could trigger specific studies towards the investigation of neuronal hyperexcitability as disease biomarker. Furthermore the identification of compounds able to rescue the phenotypes induced by DPP6 loss, could be helpful to design clinical research studies. The completion of this pilot project will allow us to meet our proposed goal to understand the role of neuronal hyperexcitability in the pathophysiology of dementia and to identify specific compounds able to rescue this dysregulation.

Researcher(s)

• Promoter: Cacace Rita

Research team(s)

Project website

Project type(s)

• Research Project

Abstract

Using advanced genetic and genomic studies, as well as expression studies in brain tissue of patients and electrophysiological modelling in Xenopus laevis oocytes, we identified dipeptidyl peptidase 6 (DPP6) as novel candidate gene in neurodegenerative brain diseases (NBD) (Cacace et al., Journal of Neurochemistry (2016) 138:231-232 and Cacace et al., under revision). Our results suggested a loss-of-function mechanism leading to the dysregulation of the normal DPP6 function in relation to its molecular partner, the potassium channel Kv4.2. In this project proposal, we plan the follow-up of our genetic findings. We hypothesize that loss of DPP6 could be crucial in alteration of brain network activity and consequentially neuronal hyperexcitability and neurodegeneration. We aim to disentangle this hypothesis using in-vitro studies in both patients' brain tissue and in cellular models, as well as in vivo studies to establish the validity of the DPP6 KO mouse model in NBD. This project aims to understand the entity of pathological consequences of DPP6/Kv4.2 dysregulation in relation to NBDs. The project outcomes will represent a fundamental milestone for novel assumptions on disease mechanism(s). Our final goal is to develop an in-vitro assay for compound testing, with a (long-term) translational application such as the development of (more personalized) preventive/efficacious therapeutic interventions.

Researcher(s)

• Promoter: Van Broeckhoven Christine
• Fellow: Cacace Rita

Research team(s)

Project type(s)

• Research Project

Abstract

Advanced genetic and genomic studies as well as expression studies in brain tissue of patients and electrophysiological modelling in Xenopus laevis oocytes, performed by our research group, identified DPP6 as novel candidate gene associated with frontotemporal dementia (FTD) (Cacace et al., under revision). Our results suggested a possible loss-of-function mechanism, leading to synaptic hyperexcitability due to dysregulation of the normal DPP6 function in relation to its molecular partner, the potassium channel Kv4.2. Based on our previous data as well as literature information, we hypothesize that DPP6 might be a crucial protein in brain neurodegeneration. In this project proposal, we aim to disentangle this hypothesis by pursuing it from different angles. We aim to investigate the brain expression of both DPP6 and Kv4.2 in additional dementia patients, independently of their genetic cause. We will investigate if a direct interaction between DPP6 and other known dementia proteins exist. Moreover, we will perform in-vitro studies to detect mutation-specific characteristics by protein stability and localization assays. In order to frame our data in a comprehensive picture, we will perform a pilot study using a Dpp6-KO mouse model in which we will evaluate whether a specific pattern of alteration in the protein orthologues of the known dementia genes is present. This project proposal and its outcome will represent a fundamental milestone to understand how extensive the DPP6/Kv4.2 dysregulation in neurodegenerative brain diseases (NBD) can be. The resulting knowledge will allow novel speculations on disease mechanism(s) and will trigger novel projects and long-term research.

Researcher(s)

• Promoter: Cacace Rita

Research team(s)

Project type(s)

• Research Project