The mRNA-Binding Protein RBM3 Regulates Activity Patterns and Local Synaptic Translation in Cultured Hippocampal Neurons

Therapeutic Hypothermia Increases the Expression of RNA-binding Protein Motif 3 and Attenuates Cognitive Deficits Following Cardiac Arrest in Rats

Cardiac arrest (CA) remains a leading cause of mortality and morbidity worldwide. Cognitive deficits are common neurological sequelae among CA survivors. Preclinical and clinical studies have confirmed that therapeutic hypothermia (TH) is an effective intervention for mitigating brain injury following CA. Hypothermia induces the expression of specific small proteins, including RNA-binding motif protein 3 (RBM3), which provides neuroprotection under stress conditions. However, the role of RBM3 in TH after CA has not been fully elucidated. In this study, we investigated the role of RBM3 in attenuating cognitive deficits following hypothermic brain resuscitation. We constructed a rat model of CA and resuscitation, and used shRNA transfection to interfere with RBM3 expression to explore the underlying mechanisms of TH's effects on cognitive alterations. Rats were randomly assigned to one of five groups: sham group (Sham), CA group (CA), TH group (TH), adeno-associated virus (AAV)-shRNA-RBM3 transfection group (shRNA-RBM3), and AAV-shRNA-negative control transfection group (shRNA-control). Key synaptic regulatory proteins, dendritic spines, and synaptic ultrastructures were examined. The rats exhibited spatial learning and memory impairments in the Morris water maze test and novel object recognition task. Hypothermia increased RBM3 expression in hippocampal neurons, mitigated early brain injury, preserved dendritic spine integrity and synaptic ultrastructure, upregulated key synaptic regulatory proteins, and ameliorated cognitive impairment following resuscitation. When RBM3 expression in the hippocampus was inhibited, the beneficial effects of therapeutic hypothermia were partially reversed. Overall, our findings provide new insights into the mechanisms of hypothermia-induced neuroprotection, demonstrating that neuroplasticity and rehabilitation can be achieved following global cerebral ischemia-reperfusion injury after CA. Therefore, the RBM3-mediated cold shock pathway represents a potential target for enhancing neuroprotection and neurorehabilitation through hypothermia.

Therapeutic modulation of protein RBM3 for ischemic stroke treatment

Several preclinical assays and clinical trials have found hypothermia as an efficient protective treatment for stroke. However, systemic hypothermia impairs several physiological functions being difficult to implement in acute critical patients. A deeper understanding of the mechanisms underlying the therapeutic effects of hypothermia could inspire new treatments based on the protective effects of cold. Furthermore, this could contribute to the reduction of the side effects associated with it. One of the metabolic landmarks of hypothermia is the overexpression of a small subset of shock proteins while global protein synthesis is reduced. Among these cold-shock proteins, RBM3 (RNA-binding motif protein 3) seems to play a central protective role. In physiological conditions, which is involved in the regulation of protein synthesis. In several models of cerebral diseases, in vitro and in vivo, RBM3 exhibited the ability to mitigate apoptosis or increase neural proliferation. In stroke models, RBM3 has shown specially promising effects attenuating neural damage and enhancing cell survival. Future prospects should be directed towards the design of efficient strategies to modulate RBM3 levels. This mini-review aims to summarize the progress made in understanding the role of RBM3 in cerebral tissue protection, while encouraging efforts to address research gaps, particularly in its modulation and clinical application.

High-resolution analysis of bound Ca2+ in neurons and synapses

Calcium (Ca2+) is a well-known second messenger in all cells, and is especially relevant for neuronal activity. Neuronal Ca2+ is found in different forms, with a minority being freely soluble in the cell and more than 99% being bound to proteins. Free Ca2+ has received much attention over the last few decades, but protein-bound Ca2+ has been difficult to analyze. Here, we introduce correlative fluorescence and nanoscale secondary ion mass spectrometry imaging as a tool to describe bound Ca2+ As expected, bound Ca2+ is ubiquitous. It does not correlate to free Ca2+ dynamics at the whole-neuron level, but does correlate significantly to the intensity of markers for GABAergic pre-synapse and glutamatergic post-synapses. In contrast, a negative correlation to pre-synaptic activity was observed, with lower levels of bound Ca2+ observed in the more active synapses. We conclude that bound Ca2+ may regulate neuronal activity and should receive more attention in the future.

FGF21 modulates hippocampal cold-shock proteins and CA2-subregion proteins in neonatal mice with hypoxia-ischemia

BACKGROUND

Fibroblast growth factor 21 (FGF21) is a neuroprotectant with cognitive enhancing effects but with poorly characterized mechanism(s) of action, particularly in females. Prior studies suggest that FGF21 may regulate cold-shock proteins (CSPs) and CA2-marker proteins in the hippocampus but empirical evidence is lacking.

METHODS

We assessed in normothermic postnatal day (PND) 10 female mice, if hypoxic-ischemic (HI) brain injury (25 min 8% O2/92% N2) altered endogenous levels of FGF21 in serum or in the hippocampus, or its receptor β-klotho. We also tested if systemic administration of FGF21 (1.5 mg/kg) modulated hippocampal CSPs or CA2 proteins. Finally, we measured if FGF21 therapy altered markers of acute hippocampal injury.

RESULTS

HI increased endogenous serum FGF21 (24 h), hippocampal tissue FGF21 (4d), and decreased hippocampal β-klotho levels (4d). Exogenous FGF21 therapy modulated hippocampal CSP levels, and dynamically altered hippocampal CA2 marker expression (24 h and 4d). Finally, FGF21 ameliorated neuronal damage markers at 24 h but did not affect GFAP (astrogliosis) or Iba1 (microgliosis) levels at 4d.

CONCLUSIONS

FGF21 therapy modulates CSP and CA2 protein levels in the injured hippocampus. These proteins serve different biological functions, but our findings suggest that FGF21 administration modulates them in a homeostatic manner after HI.

IMPACT

Hypoxic-ischemic (HI) injury in female post-natal day (PND) 10 mice decreases hippocampal RNA binding motif 3 (RBM3) levels in the normothermic newborn brain. HI injury in normothermic newborn female mice alters serum and hippocampal fibroblast growth factor 21 (FGF21) levels 24 h post-injury. HI injury in normothermic newborn female mice alters hippocampal levels of N-terminal EF-hand calcium binding protein 2 (NECAB2) in a time-dependent manner. Exogenous FGF21 therapy ameliorates the HI-mediated loss of hippocampal cold-induced RNA-binding protein (CIRBP). Exogenous FGF21 therapy modulates hippocampal levels of CA2-marker proteins after HI.

Muscleblind-1 interacts with tubulin mRNAs to regulate the microtubule cytoskeleton in C. elegans mechanosensory neurons

Regulation of the microtubule cytoskeleton is crucial for the development and maintenance of neuronal architecture, and recent studies have highlighted the significance of regulated RNA processing in the establishment and maintenance of neural circuits. In a genetic screen conducted using mechanosensory neurons of C. elegans, we identified a mutation in muscleblind-1/mbl-1 as a suppressor of loss of kinesin-13 family microtubule destabilizing factor klp-7. Muscleblind-1(MBL-1) is an RNA-binding protein that regulates the splicing, localization, and stability of RNA. Our findings demonstrate that mbl-1 is required cell-autonomously for axon growth and proper synapse positioning in the posterior lateral microtubule (PLM) neuron. Loss of mbl-1 leads to increased microtubule dynamics and mixed orientation of microtubules in the anterior neurite of PLM. These defects are also accompanied by abnormal axonal transport of the synaptic protein RAB-3 and reduction of gentle touch sensation in mbl-1 mutant. Our data also revealed that mbl-1 is genetically epistatic to mec-7 (β tubulin) and mec-12 (α tubulin) in regulating axon growth. Furthermore, mbl-1 is epistatic to sad-1, an ortholog of BRSK/Brain specific-serine/threonine kinase and a known regulator of synaptic machinery, for synapse formation at the correct location of the PLM neurite. Notably, the immunoprecipitation of MBL-1 resulted in the co-purification of mec-7, mec-12, and sad-1 mRNAs, suggesting a direct interaction between MBL-1 and these transcripts. Additionally, mbl-1 mutants exhibited reduced levels and stability of mec-7 and mec-12 transcripts. Our study establishes a previously unknown link between RNA-binding proteins and cytoskeletal machinery, highlighting their crucial roles in the development and maintenance of the nervous system.

Chronic social stress blunts core body temperature and molecular rhythms of Rbm3 and Cirbp in mouse lateral habenula

Chronic social stress in mice causes behavioural and physiological changes that result in perturbed rhythms of body temperature, activity and sleep-wake cycle. To further understand the link between mood disorders and temperature rhythmicity in mice that are resilient or susceptible to stress, we measured core body temperature (Tcore) before and after exposure to chronic social defeat stress (CSDS). We found that Tcore amplitudes of stress-resilient and susceptible mice are dampened during exposure to CSDS. However, following CSDS, resilient mice recovered temperature amplitude faster than susceptible mice. Furthermore, the interdaily stability (IS) of temperature rhythms was fragmented in stress-exposed mice during CSDS, which recovered to control levels following stress. There were minimal changes in locomotor activity after stress exposure which correlates with regular rhythmic expression of Prok2 - an output signal of the suprachiasmatic nucleus. We also determined that expression of thermosensitive genes Rbm3 and Cirbp in the lateral habenula (LHb) were blunted 1 day after CSDS. Rhythmic expression of these genes recovered 10 days later. Overall, we show that CSDS blunts Tcore and thermosensitive gene rhythms. Tcore rhythm recovery is faster in stress-resilient mice, but Rbm3 and Cirbp recovery is uniform across the phenotypes.

Chronic social stress blunts core body temperature and molecular rhythms ofRbm3andCirbpin mouse lateral habenula.. [DOI: 10.1101/2023.01.02.522528]

Chronic social stress in mice causes behavioral and physiological changes that result in perturbed rhythms of body temperature, activity and sleep-wake cycle. To further understand the link between mood disorders and temperature rhythmicity in mice that are resilient or susceptible to stress, we measured core body temperature (Tcore) before and after exposure to chronic social defeat stress (CSDS). We found that Tcore amplitudes of stress-resilient and susceptible mice are dampened during exposure to CSDS. However, following CSDS, resilient mice recovered temperature amplitude faster than susceptible mice. Furthermore, the interdaily stability (IS) of temperature rhythms was fragmented in stress-exposed mice during CSDS, which recovered to control levels following stress. There were minimal changes in locomotor activity after stress exposure which correlates with regular rhythmic expression ofProk2- an output signal of the suprachiasmatic nucleus. We also determined that expression of thermosensitive genesRbm3andCirbpin the lateral habenula (LHb) were blunted 1-day after CSDS. Rhythmic expression of these genes recovered 10 days later. Overall, we show that CSDS blunts Tcore and thermosensitive gene rhythms. Tcore rhythm recovery is faster in stress-resilient mice, butRbm3andCirbprecovery is uniform across the phenotypes.

Transcriptome Profile in the Mouse Brain of Hepatic Encephalopathy and Alzheimer's Disease

Hepatic encephalopathy (HE) is a chronic metabolic disease accompanied by neuropathological and neuropsychiatric features, including memory deficits, psychomotor dysfunction, depression, and anxiety. Alzheimer's disease (AD), the most common neurodegenerative disease, is characterized by tau hyperphosphorylation, excessive amyloid beta (Aβ) accumulation, the formation of fibrillary tangles, hippocampus atrophy, and neuroinflammation. Recent studies have suggested a positive correlation between HE and AD. Some studies reported that an impaired cholesterol pathway, abnormal bile acid secretion, excessive ammonia level, impaired Aβ clearance, astrocytic dysfunction, and abnormal γ-aminobutyric acid GABAergic neuronal signaling in HE may also be involved in AD pathology. However, the mechanisms and related genes involved in AD-like pathology in the HE brain are unclear. Thus, we compared the cortical transcriptome profile between an HE mouse model, bile duct ligation (BDL), and an AD mouse model, the 5×FAD. Our study showed that the expression of many genes implicated in HE is associated with neuronal dysfunction in AD mice. We found changes in various protein-coding RNAs, implicated in synapses, neurogenesis, neuron projection, neuron differentiation, and neurite outgrowth, and non-coding RNAs possibly associated with neuropathology. Our data provide an important resource for further studies to elucidate AD-like pathophysiology in HE patients.

Cold shock protein RBM3 is upregulated in the autophagy-deficient brain

Neural autophagy plays an important role in regulating protein quality control, brain homeostasis, and body temperature. However, the mechanism that links a defect in autophagy to body temperature has not been elucidated. Here, we report that RNA binding motif protein 3 (RBM3) is a potential candidate that regulates body temperature. We found that the body temperatures of Nestin-Cre ; Atg7 ^f/f conditional KO (cKO) mice were lower than that of wild-type (WT) mice. Moreover, RBM3 was upregulated in the Nestin-Cre ; Atg7 ^f/f brain. These data suggest that RBM3 is an implicit target that maintains body temperature influenced by neural autophagy.

Temperature-dependent structural plasticity of hippocampal synapses

The function of the central nervous system (CNS) is strongly affected by temperature. However, the underlying processes remain poorly understood. Here, we show that hypothermia and hyperthermia trigger bidirectional re-organization of presynaptic architecture in hippocampal neurons, resulting in synaptic strengthening, and weakening, respectively. Furthermore, hypothermia remodels inhibitory postsynaptic scaffold into enlarged, sparse synapses enriched in GABAA receptors. This process does not require protein translation, and instead is regulated by actin dynamics. Induction of hypothermia in vivo enhances inhibitory synapses in the hippocampus, but not in the cortex. This is confirmed by the proteomic analysis of cortical synapses, which reveals few temperature-dependent changes in synaptic content. Our results reveal a region-specific form of environmental synaptic plasticity with a mechanism distinct from the classic temperature shock response, which may underlie functional response of CNS to temperature.

Studies on the molecular level changes and potential resistance mechanism of Coreius guichenoti under temperature stimulation

In this study, we used transcriptome and proteome technology to analyze molecular level changes in tissues of Coreius guichenoti cultured at high temperature (HT) and low temperature (LT). We also screened for specific anti-stress genes and proteins and evaluated the relationships between them. We identified 201,803 unigenes and 10,623 proteins. Compared with the normal temperature (NT), 408 genes and 1,204 proteins were up- or down-regulated in brain tissues, respectively, at HT, and the numbers were 8 and 149 at LT. In gill tissues, the numbers were 101 and 1,745 at HT and 27 and 511 at LT. In gill tissues at both temperatures, the degree of down-regulation (average, HT 204.67-fold, LT 443.13-fold) was much greater than that of up-regulation (average, HT 28.69-fold, LT 17.68-fold). The protein expression in brain (average, up 52.67-fold, down 13.54-fold) and gill (average, up 73.02-fold, down 12.92-fold) tissues increased more at HT than at LT. The protein expression in brain (up 3.77-fold, down 4.79-fold) tissues decreased more at LT than at HT, whereas the protein expression in gill (up 8.64-fold, down 4.35-fold) tissues was up-regulated more at LT than at HT. At HT, brain tissues were mainly enriched in pathways related to metabolism and DNA repair; at LT, they were mainly enriched in cancer-related pathways. At both temperatures, gill tissues were mainly enriched in pathways related to cell proliferation, apoptosis, immunity, and inflammation. Additionally, Kyoto Encyclopedia of Genes and Genomes pathway analysis showed more differentially expressed proteins in gill tissues than in brain tissues at HT and LT, and temperature stimulation led to the strengthening of metabolic pathways in both tissues. Of the 96 genes we identified as potentially being highly related to temperature stress (59 from transcriptome and 38 from proteome data), we detected heat shock protein 70 in both the transcriptome and proteome. Our results improved our understanding of the differential relationship between gene expression and protein expression in C. guichenoti. Identifying important temperature stress genes will help lay a foundation for cultivating C. guichenoti, and even other fish species, that are resistant to HT or LT.

RBM3 is an outstanding cold shock protein with multiple physiological functions beyond hypothermia

RNA-binding motif protein 3 (RBM3), an outstanding cold shock protein, is rapidly upregulated to ensure homeostasis and survival in a cold environment, which is an important physiological mechanism in response to cold stress. Meanwhile, RBM3 has multiple physiological functions and participates in the regulation of various cellular physiological processes, such as antiapoptosis, circadian rhythm, cell cycle, reproduction, and tumogenesis. The structure, conservation, and tissue distribution of RBM3 in human are demonstrated in this review. Herein, the multiple physiological functions of RBM3 were summarized based on recent research advances. Meanwhile, the cytoprotective mechanism of RBM3 during stress under various adverse conditions and its regulation of transcription were discussed. In addition, the neuroprotection of RBM3 and its oncogenic role and controversy in various cancers were investigated in our review.

Hypoxia-ischemia-mediated effects on neurodevelopmentally regulated cold-shock proteins in neonatal mice under strict temperature control

BACKGROUND

Neonates have high levels of cold-shock proteins (CSPs) in the normothermic brain for a limited period following birth. Hypoxic-ischemic (HI) insults in term infants produce neonatal encephalopathy (NE), and it remains unclear whether HI-induced pathology alters baseline CSP expression in the normothermic brain.

METHODS

Here we established a version of the Rice-Vannucci model in PND 10 mice that incorporates rigorous temperature control.

RESULTS

Common carotid artery (CCA)-ligation plus 25 min hypoxia (8% O2) in pups with targeted normothermia resulted in classic histopathological changes including increased hippocampal degeneration, astrogliosis, microgliosis, white matter changes, and cell signaling perturbations. Serial assessment of cortical, thalamic, and hippocampal RNA-binding motif 3 (RBM3), cold-inducible RNA binding protein (CIRBP), and reticulon-3 (RTN3) revealed a rapid age-dependent decrease in levels in sham and injured pups. CSPs were minimally affected by HI and the age point of lowest expression (PND 18) coincided with the timing at which heat-generating mechanisms mature in mice.

CONCLUSIONS

The findings suggest the need to determine whether optimized therapeutic hypothermia (depth and duration) can prevent the age-related decline in neuroprotective CSPs like RBM3 in the brain, and improve outcomes during critical phases of secondary injury and recovery after NE.

IMPACT

The rapid decrease in endogenous neuroprotective cold-shock proteins (CSPs) in the normothermic cortex, thalamus, and hippocampus from postnatal day (PND) 11-18, coincides with the timing of thermogenesis maturation in neonatal mice. Hypoxia-ischemia (HI) has a minor impact on the normal age-dependent decline in brain CSP levels in neonates maintained normothermic post-injury. HI robustly disrupts the expected correlation in RNA-binding motif 3 (RBM3) and reticulon-3 (RTN3). The potent neuroprotectant RBM3 is not increased 1-4 days after HI in a mouse model of neonatal encephalopathy (NE) in the term newborn and in which rigorous temperature control prevents the manifestation of endogenous post-insult hypothermia.

Differences in synaptic vesicle pool behavior between male and female hippocampal cultured neurons

A strong focus on sex-related differences has arisen recently in neurobiology, but most investigations focus on brain function in vivo, ignoring common experimental models like cultured neurons. A few studies have addressed morphological differences between male and female neurons in culture, but very few works focused on functional aspects, and especially on presynaptic function. To fill this gap, we studied here functional parameters of synaptic vesicle recycling in hippocampal cultures from male and female rats, which are a standard model system for many laboratories. We found that, although the total vesicle pools are similar, the recycling pool of male synapses was larger, and was more frequently used. This was in line with the observation that the male synapses engaged in stronger local translation. Nevertheless, the general network activity of the neurons was similar, and only small differences could be found when stimulating the cultures. We also found only limited differences in several other assays. We conclude that, albeit these cultures are similar in behavior, future studies of synapse behavior in culture should take the sex of the animals into account.

TrkB signaling regulates the cold-shock protein RBM3-mediated neuroprotection

Increasing levels of the cold-shock protein, RNA-binding motif 3 (RBM3), either through cooling or by ectopic over-expression, prevents synapse and neuronal loss in mouse models of neurodegeneration. To exploit this process therapeutically requires an understanding of mechanisms controlling cold-induced RBM3 expression. Here, we show that cooling increases RBM3 through activation of TrkB via PLCγ1 and pCREB signaling. RBM3, in turn, has a hitherto unrecognized negative feedback on TrkB-induced ERK activation through induction of its specific phosphatase, DUSP6. Thus, RBM3 mediates structural plasticity through a distinct, non-canonical activation of TrkB signaling, which is abolished in RBM3-null neurons. Both genetic reduction and pharmacological antagonism of TrkB and its downstream mediators abrogate cooling-induced RBM3 induction and prevent structural plasticity, whereas TrkB inhibition similarly prevents RBM3 induction and the neuroprotective effects of cooling in prion-diseased mice. Conversely, TrkB agonism induces RBM3 without cooling, preventing synapse loss and neurodegeneration. TrkB signaling is, therefore, necessary for the induction of RBM3 and related neuroprotective effects and provides a target by which RBM3-mediated synapse-regenerative therapies in neurodegenerative disorders can be used therapeutically without the need for inducing hypothermia.