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Project

Restoring cognitive functions in neurodegenerative disease models.

The word ‘homeostasis’ is derived from two Greek words: ὅμοιος (homoios), which means ‘similar’ and στάσις (stasis), which translates to ‘standing still’. Homeostasis thus refers to the tendency of a system to maintain a stable, relatively constant internal environment, regardless of the outside changing conditions. The nervous and endocrine systems are responsible for maintaining homeostasis in the human body. For this, they rely on chemical signaling molecules, including neuropeptides that can act as fast neurotransmitters, neuromodulators and neurohormones. In this study, we exploited the power of the model organism Caenorhabditis elegans to unravel the evolutionary origin of the thyrotropin-releasing hormone (TRH) neuropeptidergic signaling system, and to shed light on its ancient function(s) and mode of action.
The neuropeptide TRH is one of the major endocrine factors that regulate vertebrate physiology. TRH acts as a multifunctional hypophysiotropic factor, stimulating the release of different hormones from the anterior pituitary gland, depending on the species. In addition, TRH exerts a large and diverse array of neuromodulatory and neuroendocrine actions in the central nervous system and periphery. However, little is known about the mechanisms underlying the central and peripheral actions of extrahypothalamic TRH. Furthermore, a functional equivalent of TRH neuropeptides in protostomian animals remains unknown, although TRH receptors are conserved in proto- and deuterostomians.
Using a combined in silico and library-based reverse pharmacology approach, we were able to molecularly characterize the C. elegans TRH-like signaling system. (R)GRELF-NH2 and (R)ANELF-NH2, two peptides encoded by the newly predicted TRH-like neuropeptide precursor TRH-1 (C30H6.10), were shown to be the cognate ligands of the nematode’s TRH receptor (TRHR) ortholog. Alanine scanning further revealed that the C-terminal tripeptide motif ELF-NH2 is crucial for molecular recognition and receptor activation. TRH-1 peptides were also able to activate the Platynereis and human TRHRs in cell culture cells, supporting the homology of TRH-1 to deuterostomian TRH precursors. Besides C. elegans TRH-1, our bioinformatics search for TRH precursor orthologs identified TRH-like sequences in the genomes of all major protostomian phyla of the Ecdysozoa (nematodes and arthropods) and Lophotrochozoa (annelids and mollusks), indicating that TRH-1 belongs to a bilaterian-wide family of TRH precursors.
Next, we examined the cellular distribution of the TRH-1 precursor and receptor using fluorescent reporter transgenes. Expression analysis showed that TRH-1 is restricted to the pharyngeal motor neurons M4 and M5, whereas TRHR-1 is localized to pharyngeal muscles pm4 and pm5. Guided by our in vivo localization study and known functions of TRH signaling in vertebrates, we set up different experiments to explore the biological actions of the TRH-1 neuropeptidergic system in the worm. Using RNAi and CRISPR/Cas9 reverse genetics, we discovered that TRH-related signaling in the pharynx promotes C. elegans growth, and that this effect depends on the bacterial diet. While trh-1 mutants fed the laboratory food source Escherichia coli OP50 are growth-defective, they have a normal body volume when growing on the high-quality food source HB101. Besides a reduced growth, mutants deficient in TRH-1 signaling also have a lower number of viable offspring, which may indicate a role for TRH-1 in the regulation of C. elegans reproduction.
Taken together, our study reveals that TRH is an evolutionarily ancient neuropeptide, having its origin prior to the divergence of protostomes and deuterostomes, more than 670 million years ago. Furthermore, our results provide first evidence of a functional TRH neuropeptide/receptor system in invertebrates that may ancestrally have been involved in the control of postembryonic growth and reproduction.

Date:1 Oct 2013 →  14 Nov 2017
Keywords:Neurodegenerative disease models
Disciplines:Animal biology, Genetics
Project type:PhD project