Spadin

In mice, disseminated coagulation, inflammation, and ischemia induce neurological damage that can lead to death. These symptoms result from circulating bubbles generated by a pathogenic decompression. Acute fluoxetine treatment or the presence of the TREK-1 potassium channel increases the survival rate when mice are subjected to an experimental dive/decompression protocol. This is a paradox because fluoxetine is a blocker of TREK-1 channels. First, we studied the effects of an acute dose of fluoxetine (50 mg/kg) in wild-type (WT) and TREK-1 deficient mice (knockout homozygous KO and heterozygous HET). Then, we combined the same fluoxetine treatment with a 5-day treatment protocol with spadin, in order to specifically block TREK-1 activity (KO-like mice). KO and KO-like mice were regarded as antidepressed models. In total, 167 mice (45 WTcont 46 WTflux 30 HETflux and 46 KOflux) constituting the flux-pool and 113 supplementary mice (27 KO-like 24 WTflux2 24 KO-likeflux 21 WTcont2 17 WTno dive) constituting the spad-pool were included in this study. Only 7% of KO-TREK-1 treated with fluoxetine (KOflux) and 4% of mice treated with both spadin and fluoxetine (KO-likeflux) died from decompression sickness (DCS) symptoms.

In this work, we aimed to correlate the expression of sortilin with the production of sortilin-derived propeptide (PE) during adipocyte differentiation, insulin resistance and inflammation. We also investigated the effect of spadin, a shorter analogue of PE that exerts a potent antidepressant in mice, on adipocyte functions. During adipogenesis, insulin resistance and inflammation, we measured the mRNA and protein expression of sortilin, by quantitative PCR and Western-blot, and quantified the expression of PE by a specific dosing method. We observed that the production of PE was correlated with the sortilin expression during adipogenesis. Immunostaining experiments allowed to visualize the co-localization of sortilin, PE and VAMP2 in 3T3-L1 adipocytes. TNFα treatment induced insulin resistance and a decrease of sortilin expression (mRNA and protein), correlated with the decrease of the PE production. By contrast, treatment with dexamethasone, which also induced insulin resistance, was without effect on sortilin expression and PE production. As a putative bioactive peptide, we have evaluated its autocrine effect by the use of spadin on 3T3-L1 adipocytes by performing glucose uptake and signalling experiments.

This study investigates the mechanism of action of spadin, a putative fast-acting peptidic antidepressant (AD) and a functional blocker of the K(+) TREK-1 channel, in relation with the medial prefrontal cortex (mPFC)-dorsal raphé (DRN) serotonergic (5-HT) neurons connectivity. Spadin increased 5-HT neuron firing rate by 113%, an augmentation abolished after electrolytic lesion of the mPFC. Among the few receptor subtypes known to modulate TREK-1, the stimulation of 5-HT4 receptors and the blockade of mGluR2/3 ones both activated 5-HT impulse flow, effects also suppressed by mPFC lesion. The combination of spadin with the 5-HT4 agonist RS 67333 paradoxically reduced 5-HT firing, an effect reversed by acutely administering the 5-HT1A agonist flesinoxan. It also had a robust synergetic effect on the expression of Zif268 within the DRN. Together, these results strongly suggest that 5-HT neurons underwent a state of depolarization block, and that the mechanisms underlying the influences exerted by spadin and RS 67333 are additive and independent from each other. In contrast, the mGluR2/3 antagonist LY 341495 occluded the effect of spadin, showing that it likely depends on mPFC TREK-1 channels coupled to mGluR2/3 receptors.