The regulator of calcineurin 1 increases adenine nucleotide translocator 1 and leads to mitochondrial dysfunctions

Disruption of RNA-binding proteins in neurological disorders

RNA-binding proteins (RBPs) are multifunctional proteins essential for the regulation of RNA processing and metabolism, contributing to the maintenance of cell homeostasis by modulating the expression of target genes. Many RBPs have been associated with neuron-specific processes vital for neuronal development and survival. RBP dysfunction may result in aberrations in RNA processing, which subsequently initiate a cascade of effects. Notably, RBPs are involved in the onset and progression of neurological disorders via diverse mechanisms. Disruption of RBPs not only affects RNA processing, but also promotes the abnormal aggregation of proteins into toxic inclusion bodies, and contributes to immune responses that drive the progression of neurological diseases. In this review, we summarize recent discoveries relating to the roles of RBPs in neurological diseases, discuss their contributions to such conditions, and highlight the unique functions of these RBPs within the nervous system.

Targeting CaN/NFAT in Alzheimer's brain degeneration

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive loss of cognitive functions. While the exact causes of this debilitating disorder remain elusive, numerous investigations have characterized its two core pathologies: the presence of β-amyloid plaques and tau tangles. Additionally, multiple studies of postmortem brain tissue, as well as results from AD preclinical models, have consistently demonstrated the presence of a sustained inflammatory response. As the persistent immune response is associated with neurodegeneration, it became clear that it may also exacerbate other AD pathologies, providing a link between the initial deposition of β-amyloid plaques and the later development of neurofibrillary tangles. Initially discovered in T cells, the nuclear factor of activated T-cells (NFAT) is one of the main transcription factors driving the expression of inflammatory genes and thus regulating immune responses. NFAT-dependent production of inflammatory mediators is controlled by Ca2+-dependent protein phosphatase calcineurin (CaN), which dephosphorylates NFAT and promotes its transcriptional activity. A substantial body of evidence has demonstrated that aberrant CaN/NFAT signaling is linked to several pathologies observed in AD, including neuronal apoptosis, synaptic deficits, and glia activation. In view of this, the role of NFAT isoforms in AD has been linked to disease progression at different stages, some of which are paralleled to diminished cognitive status. The use of classical inhibitors of CaN/NFAT signaling, such as tacrolimus or cyclosporine, or adeno-associated viruses to specifically inhibit astrocytic NFAT activation, has alleviated some symptoms of AD by diminishing β-amyloid neurotoxicity and neuroinflammation. In this article, we discuss the recent findings related to the contribution of CaN/NFAT signaling to the progression of AD and highlight the possible benefits of targeting this pathway in AD treatment.

ANT1 overexpression models: Some similarities with facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disorder characterized by progressive muscle weakness. Adenine nucleotide translocator 1 (ANT1), the only 4q35 gene involved in mitochondrial function, is strongly expressed in FSHD skeletal muscle biopsies. However, its role in FSHD is unclear. In this study, we evaluated ANT1 overexpression effects in primary myoblasts from healthy controls and during Xenopus laevis organogenesis. We also compared ANT1 overexpression effects with the phenotype of FSHD muscle cells and biopsies. Here, we report that the ANT1 overexpression-induced phenotype presents some similarities with FSHD muscle cells and biopsies. ANT1-overexpressing muscle cells showed disorganized morphology, altered cytoskeletal arrangement, enhanced mitochondrial respiration/glycolysis, ROS production, oxidative stress, mitochondrial fragmentation and ultrastructure alteration, as observed in FSHD muscle cells. ANT1 overexpression in Xenopus laevis embryos affected skeletal muscle development, impaired skeletal muscle, altered mitochondrial ultrastructure and led to oxidative stress as observed in FSHD muscle biopsies. Moreover, ANT1 overexpression in X. laevis embryos affected heart structure and mitochondrial ultrastructure leading to cardiac arrhythmia, as described in some patients with FSHD. Overall our data suggest that ANT1 could contribute to mitochondria dysfunction and oxidative stress in FSHD muscle cells by modifying their bioenergetic profile associated with ROS production. Such interplay between energy metabolism and ROS production in FSHD will be of significant interest for future prospects.

Upregulation of RCAN1.4 by HIF1α alleviates OGD-induced inflammatory response in astrocytes

OBJECTIVE

Ischemic stroke is a leading cause of human mortality and long-term disability worldwide. As one of the main forms of regulator of calcineurin 1 (RCAN1), the contribution of RCAN1.4 in diverse biological and pathological conditions has been implicated. But the role of RCAN1.4 in ischemic stroke progression remains elusive. This study is to explore the expression changes and roles of RCAN1.4 in ischemic stroke as well as the underlying mechanisms for these changes and effects of RCAN1.4 in ischemic stroke.

METHODS

Middle cerebral artery occlusion model in C57BL/6J mice and oxygen-glucose deprivation (OGD) model in primary astrocytes were performed to induce the cerebral ischemic stroke. The expression pattern of RCAN1.4 was assessed using real-time quantitative PCR and western blotting in vivo and in vitro. Mechanistically, the underlying mechanism for the elevation of RCAN1.4 in the upstream was investigated. Lentiviruses were administrated, and the effect of RCAN1.4 in postischemic inflammation was clearly clarified.

RESULTS

Here we uncovered that RCAN1.4 was dramatically increased in mouse ischemic brains and OGD-induced primary astrocytes. HIF1α, activated upon OGD, significantly upregulated RCAN1.4 gene expression through specifically binding to the RCAN1.4 promoter region and activating its promoter activity. The functional hypoxia-responsive element (HRE) was located between -254 and -245 bp in the RCAN1.4 promoter region. Moreover, elevated RCAN1.4 alleviated the release of pro-inflammatory cytokines TNFα, IL1β, IL6 and reduced expression of iNOS, COX2 in primary astrocytes upon OGD, whereas RCAN1.4 silencing has the opposite effect. Of note, RCAN1.4 overexpression inhibited OGD-induced NF-κB activation in primary astrocytes, leading to decreased degradation of IκBα and reduced nuclear translocation of NF-κB/p65.

INTERPRETATION

Our results reveal a novel mechanism underscoring the upregulation of RCAN1.4 by HIF1α and the protective effect of RCAN1.4 against postischemic inflammation, suggesting its significance as a promising therapeutic target for ischemic stroke treatment.

Targeting upregulated RNA binding protein RCAN1.1: a promising strategy for neuroprotection in acute ischemic stroke

Aims

To explore the expression changes and roles of the RNA‐binding protein RCAN1.1 in acute ischemic stroke (AIS), and to preliminarily confirm the medicinal value of the RNA aptamer R1SR13 in AIS by targeting RCAN1.1.

Methods

Two mouse AIS models of middle cerebral artery occlusion (MCAO) and right common carotid artery ligation (R‐CCAL) and oxygen glucose deprivation (OGD) model of AIS in primary neurons and SH‐SY5Y were performed. The expression pattern of RCAN1.1 was assessed using real‐time quantitative PCR (RT‐qPCR) and western blotting (WB) in vivo and in vitro. The underlying mechanism for the elevation of RCAN1.1 in the upstream was investigated. Lentiviruses were administrated and the effect of RCAN1.1 in AIS was assessed by ATP level, caspase 3/7 assay, TUNEL and WB. The protective function of R1SR13 in AIS was evaluated both in vivo and in vitro.

Results

In two mouse models of AIS, RCAN1.1 mRNA and RCAN1.1 L protein were significantly upregulated in the ischemic brain tissue. The same results were detected in the OGD model of primary neurons and SH‐SY5Y. The mechanistic analysis proved that hypoxia‐inducible factor‐1α (HIF1α) could specifically activate the RCAN1.1 gene promoter through combining with the functional hypoxia‐responsive element (HRE) site (−325 to −322 bp). The increased expression of RCAN1.1 L markedly depleted ATP production and aggravated neuronal apoptosis under OGD condition. R1SR13, an antagonizing RNA aptamer of RCAN1.1, was demonstrated to reduce neuronal apoptosis caused by the elevated RCAN1.1 L in the cellular and animal models of AIS.

Conclusion

RCAN1.1 is a novel target gene of HIF1α and the functional HRE in the RCAN1.1 promoter region is −325 to −322 bp. The marked upregulation of RCAN1.1 in AIS promoted neuronal apoptosis, an effect that could be reversed by its RNA aptamer R1SR13 in vivo and in vitro. Thus, R1SR13 represents a promising strategy for neuroprotection in AIS and our study lays a theoretical foundation for it to become a clinically targeted drug.

Fungicidal Action of the Triphenylphosphonium-Driven Succinate Dehydrogenase Inhibitors Is Mediated by Reactive Oxygen Species and Suggests an Effective Resistance Management Strategy

Succinate dehydrogenase (SDH) is an effective target of SDH inhibitor (SDHI) fungicides which received more and more attention in recent years. However, there is no good solution to their rapidly growing drug resistance caused by frequent use. In this study, three triphenylphosphonium (TPP)-conjugated boscalid analogues were synthesized and tested for antifungal activities. They all, especially 2c, exhibited enhanced fungicidal activity and broader spectra compared to boscalid. The action mechanism study revealed that 2c was also an SDH inhibitor acting on the Qp site. However, the rapid accumulation of 2c in mitochondria because of TPP-targeting triggered reactive oxygen species burst in mitochondria, resulting in irreversible damage to the mitochondrial structure and function. Thus, 2c made the fungicidal activity output mode changing from mainly relying on ATP production inhibition (as traditional SDHIs) to significant damage of the cell structure and functions. This mechanism change made it difficult for plant pathogenic fungi to develop resistance to 2c and its analogues, which was of great significance for the increasingly challenging management of field resistance to SDHI fungicides.

Ischemia Injury induces mPTP opening by reducing Sirt3

Mitochondrial permeability transition pore (mPTP) opening is critical to mitochondrial apoptosis during ischemic injury. Sirtuin 3 (Sirt3) is a mitochondrial deacetylase known to play a major role in stress resistance and cell death. Our previous studies have shown that Sirt3 activates superoxide dismutase 2 and forkhead box O3a to reduce cellular reactive oxygen species. However, it is unclear the interaction between Sirt3 and mPTP and the roles they play in ischemic stroke. We used the middle cerebral artery occlusion (MCAO) model, a mouse model of stroke, to examine Sirt3 and mPTP-related protein levels. We then applied lentivirus packaged Sirt3 overexpression in HT22 cells, a mouse hippocampal neuronal cell line, to investigate the underlying mechanism. We found Sirt3 protein level was decreased in the penumbra area in MCAO mice, along with an increase in mPTP related proteins, namely voltage-dependent anion channel 1 (VDAC1) and adenine nucleotide translocator 1 (ANT1). Sirt3 overexpression suppressed the increase in VDAC1, ANT1 and cleaved caspase 3 that were induced by the serum and glucose deprivation (SGD) condition. Our studies suggest that ischemic injury induced mPTP opening and apoptosis by reducing Sirt3. It helps to identify new therapeutic targets for ischemic stroke.

Regulator of calcineurin 1 is a novel RNA-binding protein to regulate neuronal apoptosis

Posttranscriptional regulation of gene expression plays an important role in the maturation, transport, stability and translation of coding and noncoding RNAs. RNA-binding protein (RBP) is a key factor of the regulation. Regulator of calcineurin 1 (RCAN1) is a multifunctional protein involved in neurodegeneration, mitochondrial dysfunction, inflammation and protein glycosylation, and plays an important role in the pathogenesis of Down syndrome and Alzheimer's disease. In this report, we discovered that RCNA1 is a novel RNA-binding protein. A 23 nucleotide sequence of adenine nucleotide translocator (ANT1) mRNA was identified as the binding motif of RCAN1. Furthermore, we found that R1SR13, as the RNA aptamer of RCAN1 identified by SELEX, blocked RCAN1-induced inhibition of the nuclear factor of activated T cells (NFAT) and NF-κB signaling pathways, and reduced neuronal apoptosis. Taken together, our results demonstrate that RCAN1 is a novel RNA-binding protein and the RNA aptamer of RCAN1 plays a neuroprotective role.

Regulator of Calcineurin (RCAN): Beyond Down Syndrome Critical Region

The regulator of calcineurin (RCAN) was first reported as a novel gene called DSCR1, encoded in a region termed the Down syndrome critical region (DSCR) of human chromosome 21. Genome sequence comparisons across species using bioinformatics revealed three members of the RCAN gene family, RCAN1, RCAN2, and RCAN3, present in most jawed vertebrates, with one member observed in most invertebrates and fungi. RCAN is most highly expressed in brain and striated muscles, but expression has been reported in many other tissues, as well, including the heart and kidneys. Expression levels of RCAN homologs are responsive to external stressors such as reactive oxygen species, Ca2+, amyloid β, and hormonal changes and upregulated in pathological conditions, including Alzheimer's disease, cardiac hypertrophy, diabetes, and degenerative neuropathy. RCAN binding to calcineurin, a Ca2+/calmodulin-dependent phosphatase, inhibits calcineurin activity, thereby regulating different physiological events via dephosphorylation of important substrates. Novel functions of RCANs have recently emerged, indicating involvement in mitochondria homeostasis, RNA binding, circadian rhythms, obesity, and thermogenesis, some of which are calcineurin-independent. These developments suggest that besides significant contributions to DS pathologies and calcineurin regulation, RCAN is an important participant across physiological systems, suggesting it as a favorable therapeutic target.

Down Syndrome Critical Region 1 Gene, Rcan1, Helps Maintain a More Fused Mitochondrial Network

RATIONALE

The regulator of calcineurin 1 (RCAN1) inhibits CN (calcineurin), a Ca²⁺-activated protein phosphatase important in cardiac remodeling. In humans, RCAN1 is located on chromosome 21 in proximity to the Down syndrome critical region. The hearts and brains of Rcan1 KO mice are more susceptible to damage from ischemia/reperfusion (I/R); however, the underlying cause is not known.

OBJECTIVE

Mitochondria are key mediators of I/R damage. The goal of these studies was to determine the impact of RCAN1 on mitochondrial dynamics and function.

METHODS AND RESULTS

Using both neonatal and isolated adult cardiomyocytes, we show that, when RCAN1 is depleted, the mitochondrial network is more fragmented because of increased CN-dependent activation of the fission protein, DRP1 (dynamin-1-like). Mitochondria in RCAN1-depleted cardiomyocytes have reduced membrane potential, O₂ consumption, and generation of reactive oxygen species, as well as a reduced capacity for mitochondrial Ca²⁺ uptake. RCAN1-depleted cardiomyocytes were more sensitive to I/R; however, pharmacological inhibition of CN, DRP1, or CAPN (calpains; Ca²⁺-activated proteases) restored protection, suggesting that in the absence of RCAN1, CAPN-mediated damage after I/R is greater because of a decrease in the capacity of mitochondria to buffer cytoplasmic Ca²⁺. Increasing RCAN1 levels by adenoviral infection was sufficient to enhance fusion and confer protection from I/R. To examine the impact of more modest, and biologically relevant, increases in RCAN1, we compared the mitochondrial network in induced pluripotent stem cells derived from individuals with Down syndrome to that of isogenic, disomic controls. Mitochondria were more fused, and O₂ consumption was greater in the trisomic induced pluripotent stem cells; however, coupling efficiency and metabolic flexibility were compromised compared with disomic induced pluripotent stem cells. Depletion of RCAN1 from trisomic induced pluripotent stem cells was sufficient to normalize mitochondrial dynamics and function.

CONCLUSIONS

RCAN1 helps maintain a more interconnected mitochondrial network, and maintaining appropriate RCAN1 levels is important to human health and disease.