Chronic peri-adolescent stress in humans increases risk to develop a substance use disorder during adulthood. Rats reared in social isolation during peri-adolescence (aSI; 1 rat/cage) period show greater ethanol and cocaine intake compared to group housed (aGH; 4 rats/cage) rats. In addition, aSI rats have a heightened dopamine response in the nucleus accumbens (NAc) to rewarding and aversive stimuli. Furthermore, single pulse electrical stimulation in slices containing NAc core elicits greater dopamine release in aSI rats. Here, we further investigated dopamine release kinetics and machinery following aSI. Dopamine release, across a wide range of stimulation intensities and frequencies, was significantly greater in aSI rats. Interestingly, subthreshold intensity stimulations also resulted in measurable dopamine release in accumbal slices from aSI but not aGH rats. Extracellular [Ca2+] manipulations revealed augmented calcium sensitivity of dopamine release in aSI rats. The readily releasable pools of dopamine, examined by bath application of Ro-04-1284/000, a vesicular monoamine transporter 2 (VMAT2) inhibitor, were depleted faster in aGH rats. Western blot analysis of release machinery proteins (VMAT2, Synaptogyrin-3, Syntaxin-1, and Munc13-3) showed no difference between the two groups. Tyrosine hydroxylase (TH) protein expression levels, however, were elevated in aSI rats. The greater dopamine release could potentially be explained by higher levels of TH, the rate-limiting step for dopamine synthesis. This augmented responsivity of the dopamine system and heightened dopamine availability post-aSI may lead to an increased risk of addiction vulnerability.
Rapid antidepressants are novel treatments for major depressive disorder (MDD) and work by blocking N-methyl-D-aspartate receptors (NMDARs), which, in turn, activate the protein synthesis pathway regulated by mechanistic/mammalian target of rapamycin complex 1 (mTORC1). Our recent work demonstrates that the RNA-binding protein Fragile X Mental Retardation Protein (FMRP) is downregulated in dendrites upon treatment with a rapid antidepressant. Here, we show that the behavioral effects of the rapid antidepressant Ro-25-6981 require FMRP expression, and treatment promotes differential mRNA binding to FMRP in an mTORC1-dependent manner. Further, these mRNAs are identified to regulate transsynaptic signaling. Using a novel technique, we show that synapse formation underlying the behavioral effects of Ro-25-6981 requires GABABR-mediated mTORC1 activity in WT animals. Finally, we demonstrate that in an animal model that lacks FMRP expression and has clinical relevance for Fragile X Syndrome (FXS), GABABR activity is detrimental to the effects of Ro-25-6981. These effects are rescued with the combined therapy of blocking GABABRs and NMDARs, indicating that rapid antidepressants alone may not be an effective treatment for people with comorbid FXS and MDD.
Background Alzheimer’s Disease (AD) is a complex neurodegenerative disorder of the synapse, characterized by the accumulation of amyloid beta plaques and neurofibrillary tangles. We have recently shown that Parkinson Protein 7, DJ‐1, is upregulated by mTORC1 activity, and is a translational hub that is predicted to coordinate the expression of a population of synaptic proteins (Niere et al., 2016). This cellular function of DJ‐1 is mediated through its RNA‐binding properties, yet many of its target mRNAs are unidentified, and the effects of this protein‐mRNA association are not well‐defined. Method Synaptically increased DJ‐1 expression was determined by Western blotting of synaptoneurosomes from AD patients (Niere et al., 2020), and APP/PS1 and P301S mouse models of AD. DJ‐1 target mRNAs were first bioinformatically identified using a modified consensus sequence of DJ‐1 protein (van der Brug et al., 2008), and confirmed via RNA‐immunoprecipitation of DJ‐1 from WT mouse cortices. FMR1KO mouse cortices were used as a negative control. Result Synaptic DJ‐1 expression is increased in a preclinical mouse model of AD exhibiting plaque pathology, and AD patients. Interestingly, there is no change in synaptic DJ‐1 levels in the P301S mouse model, which presents neurofibrillary tangles. We bioinformatically identified that mRNA coding for the RNA‐binding protein FMRP, and tau‐tubulin kinase 1 (TTBK1), known for phosphorylating pathogenic tau, as potential targets for DJ‐1, and confirmed it via RNA‐immunoprecipitation. Furthermore, the protein levels of FMRP is significantly decreased in the synapses of AD patients and APP/PS1 mice, while there is no change in the P301S model consistent with no change in DJ‐1 expression. Conclusion Decrease in FMRP in AD synapses where DJ‐1 expression is high suggests that DJ‐1 is a translational repressor of FMRP. FMRP binds to the mRNA of amyloid precursor protein (APP), the building block of amyloid beta plaques. Therefore, DJ‐1’s capacity to bind both Fmr1, coding for a protein which is known as a translational suppressor of APP mRNA (Borreca et al., 2016), and Ttbk1, a tau kinase involved in tau phosphorylation and aggregation (Sato et al., 2006) suggests that DJ‐1 might be at the crossroads of both AD hallmark pathologies.
L-type voltage-dependent Ca2+ channels (L-VDCC) integrate synaptic signals to facilitate a plethora of cellular mechanisms. L-VDCC dysfunction is implicated in several neurological and psychiatric diseases. Despite their importance, signals upstream of L-VDCC activity that regulate their channel density, however, are poorly defined. In disease models with overactive mammalian target of rapamycin complex 1 (mTORC1) signaling (or mTORopathies), including tuberous sclerosis (TS) and Alzheimer’s disease (AD), we report a novel mechanism downstream of mTORC1 signaling that results in a deficit in dendritic L-VDCC activity. Deficits in L-VDCC activity are associated with increased expression of the mTORC1-regulated RNA-binding protein DJ-1. DJ-1 binds the mRNA coding the auxiliary Ca2+ channel subunit α2δ2 responsible for shuttling L-VDCC to the membrane and represses its expression. Moreover, this novel DJ-1/α2δ2/L-VDCC pathway is disrupted in human AD and preclinical models of AD and TS. Our discovery that DJ-1 directs L-VDCC activity and L-VDCC-associated protein α2δ2 at the synapse suggests that DJ-1/α2δ2/L-VDCC is a common, fundamental pathway disrupted in TS and AD that can be targeted in clinical mTORopathies.Significance StatementMany neurological disorders share symptoms, despite disparity among diseases. Treatments are prescribed based on diagnosis rather than individual symptoms. While only treating symptoms may obscure the disease, mechanism-based drug development allows the two approaches to converge. Hub proteins, those that coordinate the expression of proteins that mediate specific cellular functions, may be dysregulated across a broad range of disorders. Herein, we show that the RNA-binding protein DJ-1 controls the activity of L-type voltage-dependent calcium channels (L-VDCC), via the expression of its auxiliary subunit alpha2delta2 (α2δ2). Importantly, we demonstrate that this novel DJ-1/α2δ2/L-VDCC pathway is commonly disrupted among neurological disorders, namely Alzheimer’s disease (AD) and Tuberous Sclerosis (TS). Collectively, these data rationalize mechanism-based drug therapy to treat disease.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.