Alteration of twinfilin1 expression underlies opioid withdrawal-induced remodeling of actin cytoskeleton at synapses and formation of aversive memory

MeCP2 Modulates Depression-Like Behaviors Comorbid to Chronic Pain by Regulating Adult Hippocampal Neurogenesis

AIMS

Although previous studies have revealed the association between chronic pain-induced depression and defective adult hippocampal neurogenesis (AHN), the underlying molecular mechanism remains elusive. This study aims to examine the association between AHN and depression-like behaviors, and to reveal the underlying mechanisms.

METHODS

The chronic neuropathic pain model was established using mice with the spared nerve injury (SNI) surgery. The depression-like behaviors were evaluated by using the sucrose preference test (SPT), the tail suspension test (TST), the forced swimming test (FST), and the open field test (OFT). The expression of Methyl-CpG-binding protein 2 (MeCP2) was modulated by injecting the adeno-associated virus (AAV) with the DIO system into the ventral DG of the Nes-CreERT2 mice. The miRNAs in hippocampal neural stem cells (NSCs) of mice with chronic pain were analyzed via miRNA sequencing.

RESULTS

We found that MeCP2, an epigenetic factor that plays a key role in the development of neurons, was significantly down-regulated in NSCs in the dentate gyrus (DG) of the hippocampus in adult mice with chronic pain and comorbid depression, suggesting a role of MeCP2 in the regulation of depression-like behavior induced by chronic neuropathic pain. MeCP2 expression levels in hippocampal NSCs were closely related to AHN and chronic pain comorbid depression, and miR-199b-3p specifically targeted and inhibited MeCP2 expression by directly interacting with its 3'-UTR sequence. Furthermore, we demonstrated that the increased level of miR-199b-3p in NSCs after the occurrence of chronic pain was responsible for AHN inhibition and comorbid depression.

CONCLUSION

Chronic neuropathic pain may result in an increased level of miR-199b-3p in hippocampal NSCs, which in turn targeted the Mecp2 gene and inhibited its transcription. Inhibited MeCP2 expression in NSCs contributes to AHN inhibition and depression-like behaviors.

Regulation of actin dynamics by Twinfilin

Twinfilin is an evolutionarily conserved actin-binding protein initially mischaracterized as a tyrosine kinase but later recognized as a key regulator of cellular actin dynamics. As a member of the ADF-H family, twinfilin binds both actin monomers and filaments. Its role in sequestering G-actin is well-established, but its effects on actin filaments have been debated. While early studies suggested twinfilin caps filament barbed ends, later research demonstrated its role in nucleotide-specific barbed-end depolymerization. Further, it was initially thought to be a processive depolymerase. Recent structural and single-molecule studies have however challenged this view, indicating that twinfilin binding events result in the removal of only one or two actin subunits from the barbed end. Additionally, twinfilin directly binds capping protein (CP) and facilitates uncapping of CP-bound barbed ends. Here, we summarize twinfilin's cellular and tissue-specific localization, and examine its evolving role in regulating cellular actin dynamics in light of its known biochemical functions.

Tear fluid reflects the altered protein expressions of Alzheimer's disease patients in proteins involved in protein repair and clearance system or the regulation of cytoskeleton

BACKGROUND

New biomarkers that improve diagnosis of Alzheimer's disease (AD) are warranted. Tear fluid (TF) containing variety of proteins that reflect pathophysiological changes of systemic diseases makes TF proteins potential biomarker candidates for AD.

OBJECTIVE

We investigated the expression levels of TF proteins in persons with mild AD and cognitively healthy controls (CO) to find out if altered proteins may link to the AD pathophysiology.

METHODS

We analyzed the data of the 53 study participants (34 COs, mean age 71 and Mini-Mental State Examination (MMSE) 28.9 ± 1.4 and 19 persons with AD, CDR 0.5-1, mean age 71 and MMSE 23.8 ± 2.8). All went through neurological status examination, cognitive tests, and ophthalmological examination. TF was collected using Schirmer strips. The TF protein content was evaluated via mass spectrometry-based proteomics and label-free quantification.

RESULTS

Eleven proteins having a role either in protein repair and clearance system, or regulation of cytoskeleton, showed altered expression in AD group compared to CO group. Seven of them were significantly (p ≤ 0.05) upregulated (Sti1, Twf1, Myl6, Otub1, Pls1 and Caza1) or, downregulated (HSP90) in AD group.

CONCLUSIONS

Altered expression of all these up- or downregulated proteins may be linked to AD pathophysiology. Thus, our results are encouraging for searching new biomarker candidates for AD. TF is potential biomarker candidate, because TF seems to reflect altered protein levels already in mild AD dementia.

Integrative Analysis of Morphine-Induced Differential Circular RNAs and ceRNA Networks in the Medial Prefrontal Cortex

Circular RNAs (circRNAs) are a novel type of non-coding RNAs. Despite the fact that the functional mechanisms of most circRNAs remain unknown, emerging evidence indicates that circRNAs could sponge microRNAs (miRNAs), bind to RNA binding proteins (RBP), and even be translated into protein. Recent research has demonstrated the crucial roles played by circRNAs in neuropsychiatric disorders. The medial prefrontal cortex (mPFC) is a crucial component of drug reward circuitry and exerts top-down control over cognitive functions. However, there is currently limited knowledge about the correlation between circRNAs and morphine-associated contextual memory in the mPFC. Here, we performed morphine-induced conditioned place preference (CPP) in mice and extracted mPFC tissue for RNA-sequencing. Our study represented the first attempt to identify differentially expressed circRNAs (DEcircRNAs) and mRNAs (DEmRNAs) in the mPFC after morphine-induced CPP. We identified 47 significantly up-regulated DEcircRNAs and 429 significantly up-regulated DEmRNAs, along with 74 significantly down-regulated DEcircRNAs and 391 significantly down-regulated DEmRNAs. Functional analysis revealed that both DEcircRNAs and DEmRNAs were closely associated with neuroplasticity. To further validate the DEcircRNAs, we conducted qRT-PCR, Sanger sequencing, and RNase R digestion assays. Additionally, using an integrated bioinformatics approach, we constructed ceRNA networks and identified critical circRNA/miRNA/mRNA axes that contributed to the development of morphine-associated contextual memory. In summary, our study provided novel insights into the role of circRNAs in drug-related memory, specifically from the perspective of ceRNAs.

Targeting the cytoskeleton as a therapeutic approach to substance use disorders

Substance use disorders (SUD) are chronic relapsing disorders governed by continually shifting cycles of positive drug reward experiences and drug withdrawal-induced negative experiences. A large body of research points to plasticity within systems regulating emotional, motivational, and cognitive processes as drivers of continued compulsive pursuit and consumption of substances despite negative consequences. This plasticity is observed at all levels of analysis from molecules to networks, providing multiple avenues for intervention in SUD. The cytoskeleton and its regulatory proteins within neurons and glia are fundamental to the structural and functional integrity of brain processes and are potentially the major drivers of the morphological and behavioral plasticity associated with substance use. In this review, we discuss preclinical studies that provide support for targeting the brain cytoskeleton as a therapeutic approach to SUD. We focus on the interplay between actin cytoskeleton dynamics and exposure to cocaine, methamphetamine, alcohol, opioids, and nicotine and highlight preclinical studies pointing to a wide range of potential therapeutic targets, such as nonmuscle myosin II, Rac1, cofilin, prosapip 1, and drebrin. These studies broaden our understanding of substance-induced plasticity driving behaviors associated with SUD and provide new research directions for the development of SUD therapeutics.

Induction of miR-665-3p Impairs the Differentiation of Myogenic Progenitor Cells by Regulating the TWF1-YAP1 Axis

Actin dynamics are known to orchestrate various myogenic processes in progenitor cells. Twinfilin-1 (TWF1) is an actin-depolymerizing factor that plays a crucial role in the differentiation of myogenic progenitor cells. However, little is known about the mechanisms underlying the epigenetic regulation of TWF1 expression and impaired myogenic differentiation in the background of muscle wasting. This study investigated how miR-665-3p affects TWF1 expression, actin filaments' modulation, proliferation, and myogenic differentiation in progenitor cells. Palmitic acid, the most prevalent saturated fatty acid (SFA) in food, suppressed TWF1 expression and inhibited the myogenic differentiation of C2C12 cells while increasing the level of miR-665-3p expression. Interestingly, miR-665-3p inhibited TWF1 expression by targeting TWF1 3'UTR directly. In addition, miR-665-3p accumulated filamentous actin (F-actin) and enhanced the nuclear translocation of Yes-associated protein 1 (YAP1), consequently promoting cell cycle progression and proliferation. Furthermore, miR-665-3p suppressed the expressions of myogenic factors, i.e., MyoD, MyoG, and MyHC, and consequently impaired myoblast differentiation. In conclusion, this study suggests that SFA-inducible miR-665-3p suppresses TWF1 expression epigenetically and inhibits myogenic differentiation by facilitating myoblast proliferation via the F-actin/YAP1 axis.

Mir-302a/TWF1 Axis Impairs the Myogenic Differentiation of Progenitor Cells through F-Actin-Mediated YAP1 Activation

Actin cytoskeleton dynamics have been found to regulate myogenesis in various progenitor cells, and twinfilin-1 (TWF1), an actin-depolymerizing factor, plays a vital role in actin dynamics and myoblast differentiation. Nevertheless, the molecular mechanisms underlying the epigenetic regulation and biological significance of TWF1 in obesity and muscle wasting have not been explored. Here, we investigated the roles of miR-302a in TWF1 expression, actin filament modulation, proliferation, and myogenic differentiation in C2C12 progenitor cells. Palmitic acid, the most prevalent saturated fatty acid (SFA) in the diet, decreased the expression of TWF1 and impeded myogenic differentiation while increasing the miR-302a levels in C2C12 myoblasts. Interestingly, miR-302a inhibited TWF1 expression directly by targeting its 3′UTR. Furthermore, ectopic expression of miR-302a promoted cell cycle progression and proliferation by increasing the filamentous actin (F-actin) accumulation, which facilitated the nuclear translocation of Yes-associated protein 1 (YAP1). Consequently, by suppressing the expressions of myogenic factors, i.e., MyoD, MyoG, and MyHC, miR-302a impaired myoblast differentiation. Hence, this study demonstrated that SFA-inducible miR-302a suppresses TWF1 expression epigenetically and impairs myogenic differentiation by facilitating myoblast proliferation via F-actin-mediated YAP1 activation.

Upregulation of dynorphin/kappa opioid receptor system in the dorsal hippocampus contributes to morphine withdrawal-induced place aversion

Aversive emotion of opioid withdrawal generates motivational state leading to compulsive drug seeking and taking. Kappa opioid receptor (KOR) and its endogenous ligand dynorphin have been shown to participate in the regulation of aversive emotion. In the present study, we investigated the role of dynorphin/KOR system in the aversive emotion following opioid withdrawal in acute morphine-dependent mice. We found that blockade of KORs before pairing by intracerebroventricular injection of KOR antagonist norBNI (20, 40 μg) attenuated the development of morphine withdrawal-induced conditioned place aversion (CPA) behavior. We further found that morphine withdrawal increased dynorphin A expression in the dorsal hippocampus, but not in the amygdala, prefrontal cortex, nucleus accumbens, and thalamus. Microinjection of norBNI (20 μg) into the dorsal hippocampus significantly decreased morphine withdrawal-induced CPA behavior. We further found that p38 MAPK was significantly activated in the dorsal hippocampus after morphine withdrawal, and the activation of p38 MAPK was blocked by pretreatment with norBNI. Accordingly, microinjection of p38 MAPK inhibitor SB203580 (5 μg) into the dorsal hippocampus significantly decreased morphine withdrawal-produced CPA behavior. This study demonstrates that upregulation of dynorphin/KOR system in the dorsal hippocampus plays a critical role in the formation of aversive emotion associated with morphine withdrawal, suggesting that KOR antagonists may have therapeutic value for the treatment of opioid withdrawal-induced mood-related disorders.