GABA promotes survival and axonal regeneration in identifiable descending neurons after spinal cord injury in larval lampreys

Abstract

Phones : +34 881816949 and +34 881816946 Emails: anton.barreiro@usc.es and mcelina.rodicio@usc.es Running title: GABA promotes regeneration after spinal cord injury peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission.The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/280891 doi: bioRxiv preprint first posted online Mar. 12, 2018; 2 AbstractIn mammals, spinal cord injury (SCI) causes permanent disability. The poor regenerative capacity of descending neurons is one of the main causes of the lack of recovery after SCI. In addition, the prevention of retrograde degeneration leading to the atrophy or death of descending neurons is an obvious prerequisite for the activation of axonal regeneration. Lampreys show an amazing regenerative capacity after SCI.Recent histological work in lampreys suggested that GABA, which is massively released after a SCI, could promote the survival of descending neurons. Here, we aimed to study if GABA, acting through GABAB receptors, promotes the survival and axonal regeneration of descending neurons of larval sea lampreys after a complete SCI. First, we used in situ hybridization to confirm that identifiable descending neurons of late stage larvae express the gabab1 subunit of the sea lamprey GABAB receptor. We also observed an acute increase in the expression of this subunit in descending neurons after a complete SCI, which further supported the possible role of GABA and GABAB receptors in promoting the survival and regeneration of these neurons. So, we performed gain and loss of function experiments to confirm this hypothesis. Treatments with GABA and baclofen (GABAB agonist) significantly reduced caspase activation in descending neurons 2 weeks after a complete SCI. Long-term treatments with GABOB (a GABA analogue) and baclofen significantly promoted axonal regeneration of descending neurons after SCI. These data indicate that GABAergic signalling through GABAB receptors promotes the survival and regeneration of descending neurons after SCI. Finally, we used morpholinos against the gabab1 subunit to specifically knockdown the expression of the GABAB receptor in descending neurons. Long-term morpholino treatments caused a significant inhibition of axonal regeneration, which shows that endogenous GABA promotes axonal regeneration after a complete SCI in peer-reviewed)

Inhibition of Gamma-Secretase Promotes Axon Regeneration After a Complete Spinal Cord Injury

“…Specifically, this treatment led to a significant increase in the regeneration of individually identifiable descending neurons of the lamprey brainstem. This is in agreement with our previous results showing improved axon regeneration after baclofen or GABOB treatments after SCI in lampreys (Romaus-Sanjurjo et al, 2018a). So, the Notch signaling pathway appears to be of crucial importance in the regulation of axon regrowth after SCI in lampreys.…”

“…In previous work, we showed that both GABA and baclofen promote axon regeneration after a complete SCI in lampreys (Romaus-Sanjurjo et al, 2018a). Here, we aimed to identify new genes involved in axon regeneration in lampreys that might be regulated by GABAergic signaling.…”

“…In a recent study, we showed that endogenous GABA promotes axon regeneration in descending neurons of lampreys after a complete SCI, and that GABOB (a GABA analog) and baclofen (a GABAB receptor agonist) treatments further promoted axon regeneration (Romaus-Sanjurjo et al, 2018a. GABA and baclofen treatments also inhibited caspase activation in giant individually identifiable descending neurons following the complete SCI (Romaus-Sanjurjo et al, 2018a). Here, we repeated the GABA and baclofen treatments and carried out 2 independent Illumina RNA sequencing (RNA-Seq) studies in the brainstems of control non-treated animals and treated animals.…”

Taurine promotes axonal regeneration after a complete spinal cord injury in lampreys

“…18 Interestingly, recent work of our group has shown that endogenous GABA promotes axonal regeneration of identifiable reticulospinal neurons following SCI in lampreys. 19 The beneficial effects of GABA appear to be mainly mediated through the activation of GABAB receptors in injured neurons; 19 although, recent work has also shown that the activation of GABAA receptors by muscimol inhibits caspase activation in identifiable neurons after SCI in lampreys. 20 Taken together, these data prompted us to study the possible effect of taurine in axon regeneration after SCI in lampreys.…”

Importance of brain alterations in spinal cord injury

“…54 GABA/baclofen (a GABA B agonist) can reduce the caspase activity of brain neurons at 2 weeks after the complete transection of the lamprey's spinal cord, thereby inhibiting the progression of apoptosis and promoting the survival/regeneration of descending projections. 55,56 Further RNA-sequencing results revealed that GABA or baclofen treatment substantially down-regulated the HES gene and decreased the activation of the Notch signaling pathway after SCI, thus revealing a novel therapeutic target that can inhibit g-secretase activity to promote axon regeneration. 57 These studies from lamprey SCI models revealed the effects of SCI on brain structure and proposed several (and are still expanding) drugs to alleviate the death/atrophy of descending projection neurons caused by degeneration.…”