The physiological role of GABA in the peripheral nervous system

• Applicant: Dr. Hagen Wende
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells
• Term: from 2017 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 387108977

Primary sensory neurons of the peripheral nervous system (PNS) are located in dorsal root ganglia and cranial ganglia. They detect external stimuli like temperature, touch and pain and convey this information to the central nervous system (CNS). Pain is a physiological response to tissue damaging sensory stimulation and serves to protect our body. At the same time injury and inflammation can trigger pathological forms of pain, which greatly decreases the quality of life of those suffering from it. Pain management so far relies on non-steroidal anti-inflammatory drugs, paracetamol, opioids and cannabinoids, which have many inherent adverse effects. Therefore the search for specific therapeutic targets for pain treatment is one of the key goals of current research.The TRPV1 receptor is expressed in primary sensory neurons of the PNS. It has attracted a lot of attention because it serves as an integrator molecule in pain signalling. Drugs inhibiting TRPV1 unfortunately have severe side effects on thermoregulation and therefore clinical trials had to be stopped. Interestingly, we have recently shown that TRPV1 is modulated by inhibitory signalling through the GABAB1 receptor. We could also show that PNS neurons themselves release GABA, the ligand for GABAB1. Modulating this endogenous signalling pathway might therefore be an alternative route to target TRPV1. In this project I aim to characterize GABA signalling in the PNS to elucidate its role in TRPV1 modulation and pain.Using the mouse as a model system, we will perform in situ hybridization to identify genes in the GABA pathway that are expressed in the PNS. Targeting these transcripts allows us to manipulate GABA levels in vitro and in vivo. This gives us insight into the physiological role of GABA in the PNS. We showed that GABA is released from peripheral fibres upon TRPV1 activation, but how this comes about remains elusive. We will use a corneal ex vivo preparation as well as cell culture to define parameters and identify molecules involved in GABA release. These molecules will then be characterized with patch clamp recordings in HEK cells and stimulated GABA release assays in vitro. Finally I want to determine how GABAB1 signalling affects TRPV1 function on the molecular level. For this we will define interaction domains of the two receptors and use TIRF microscopy, surface biotinylation and bioluminescence resonance energy transfer to characterize TRPV1 vesicle dynamics in response to GABAB1 signalling.GABA signaling is the target for many drugs in the CNS, with tremendous beneficial effects for patients. But the role of this inhibitory signaling pathway in the peripheral nervous system has thus far escaped our attention. With this proposal I want to gain key insight into the role of GABA signaling in the PNS and I hope to advance our knowledge so that in the future we will be able to target GABA signaling in the PNS to better treat diseases such as chronic pain.

• DFG Programme: Research Grants