Survival Motor Neuron (SMN) Protein Insufficiency Exacerbates Renal Ischemia/Reperfusion Injury

SMN haploinsufficiency promotes ischemia/ reperfusion-induced AKI-to-CKD transition by endoplasmic reticulum stress activation

Acute kidney injury (AKI) and chronic kidney disease (CKD) are interconnected syndromes that represent a global public health challenge. Here, we identified a specific role of survival of motor neuron (SMN) in ischemia/reperfusion (I/R)-induced kidney injury and progression of CKD. SMN was an essential protein in all cell type and was reported to play important roles in multiple fundamental cellular homeostatic pathways. However, the function of SMN in experimental models of I/R-induced kidney fibrosis has not extensively studied. Genetic ablation of SMN or small interfering RNA-base knockdown of SMN expression aggravated the tubular injury and interstitial fibrosis. Administration of scAAV9-CB-SMN or epithelial cell overexpression of SMN reduced I/R-induced kidney dysfunction and attenuated AKI-to-CKD transition, indicating that SMN is vital for the preservation and recovery of tubular phenotype. Our data showed that the endoplasmic reticulum stress (ERS) induced by I/R was persistent and became progressively more severe in the kidney without SMN. On the contrary, overexpression of SMN prevented against I/R-induced ERS and tubular cell damage. In summary, our data collectively substantiate a critical role of SMN in regulating the ERS activation and phenotype of AKI-to-CKD transition that may contribute to renal pathology during injury and repair.

Spinal Muscular Atrophy Type IIIb Complicated by Moyamoya Syndrome: A Case Report and Literature Review

Spinal muscular atrophy (SMA) is an inherited disorder characterized by degeneration of motor neurons and symmetrical muscle weakness and atrophy. Moyamoya syndrome (MMS) or moyamoya disease (MMD) is radiologically defined by chronic cerebrovascular occlusion with abnormal vascular network formation in the skull base. We report herein a 21-year-old female patient with limb weakness and muscular atrophy for 17 years. Electromyography revealed extensive motor neuron damage. Cranial MRA showed occlusion of bilateral anterior and middle cerebral arteries, with increased peripheral blood vessels and collateral circulation. She was diagnosed as SMA type IIIb combined with MMS following genetic testing, in which homozygous deletion of exons 7 and 8 of survival motor neuron (SMN)1 gene and 3 copies of exons 7 and 8 of SMN2 gene were detected. After treatment, the patient's symptoms improved. Our study found that the rare SMA and MMS co-exist. We speculated that the moyamoya phenomenon may be related to the abnormal regulation of intracranial vascular endothelial cells and smooth muscle cells in proliferation and differentiation caused by functional defects of SMN protein. The relationship between the two diseases needs to be further elucidated in future clinical work.

Downregulation of lncRNA TUG1 attenuates inflammation and apoptosis of renal tubular epithelial cell induced by ischemia-reperfusion by sponging miR-449b-5p via targeting HMGB1 and MMP2

We aimed to evaluate the functions of long non-coding RNA taurine upregulated gene 1 (lncRNA TUG1) in renal ischemia-reperfusion (I/R) injury and identify the potential mechanisms. Pathological changes of renal tissues were examined using H&E staining after mimic renal I/R injury in vivo. The contents of serum renal functional parameters and inflammatory factors were measured. The expression of TUG1 and miR-449b-5p in renal tissues and HK-2 cells stimulated by I/R were detected. Then, the effects of TUG1 silencing on inflammation and apoptosis of cells were evaluated. Dual luciferase reporter assays were executed for determining the correlation between miR-449b-5p and TUG1, high mobility group box 1 (HMGB1), or matrix metalloproteinase 2 (MMP2). Subsequently, cells were co-transfected with miR-449b-5p mimic and pcDNA3.1 TUG1. The levels of inflammation, apoptosis, and the expression of HMGB1 and MMP2 were detected. The results revealed that renal tissues were obviously damaged after I/R accompanied by changes in renal functional markers and inflammatory factors. TUG1 was highly expressed whereas miR-449b-5p was lowly expressed. TUG1 silencing reduced the inflammation and apoptosis. Dual luciferase reporter assays confirmed that miR-449b-5p was a target of TUG1 as well as HMGB1 and MMP2 were direct targets of miR-449b-5p. Meanwhile, miR-449b-5p mimic presented the same results with TUG1 silencing, which were reversed after TUG1 overexpression. Moreover, MMP2 and HMGB1 expression was decreased after miR-449b-5p overexpression while that of was increased after TUG1 overexpression. These findings demonstrated that TUG1 silencing attenuates I/R-induced inflammation and apoptosis via targeting miR-449b-5p and regulating HMGB1 and MMP2 expression.

Spinal muscular atrophy: Broad disease spectrum and sex-specific phenotypes

Spinal muscular atrophy (SMA) is one of the major genetic disorders associated with infant mortality. More than 90% of cases of SMA result from deletions of or mutations in the Survival Motor Neuron 1 (SMN1) gene. SMN2, a nearly identical copy of SMN1, does not compensate for the loss of SMN1 due to predominant skipping of exon 7. The spectrum of SMA is broad, ranging from prenatal death to infant mortality to survival into adulthood. All tissues, including brain, spinal cord, bone, skeletal muscle, heart, lung, liver, pancreas, gastrointestinal tract, kidney, spleen, ovary and testis, are directly and/or indirectly affected in SMA. Accumulating evidence on impaired mitochondrial biogenesis and defects in X chromosome-linked modifying factors, coupled with the sexual dimorphic nature of many tissues, point to sex-specific vulnerabilities in SMA. Here we review the role of sex in the pathogenesis of SMA.

Survival motor neuron protein protects H9c2 cardiomyocytes from hypoxia-induced cell injury by reducing apoptosis

BACKGROUND

Hypoxia induces cell injury in cardiomyocytes and leads to the development of cardiovascular diseases. The survival motor neuron protein (SMN) is a crucial ubiquitous protein whose functional deficiency causes motor neuron loss seen in spinal muscular atrophy. SMN has shown protective effects on the cardiovascular system and the aim of the present study was to investigate the cardioprotective effects of SMN on hypoxia-induced cell injury.

METHODS

Cobalt chloride (CoCl2 ) was used to induce chemical hypoxia in H9c2 cardiomyocytes. Cell proliferation was determined by the MTT assay and the mRNA levels of SMN were evaluated by real-time polymerase chain reaction. The protein expression levels of SMN, hypoxia-inducible transcription factor 1α (HIF-1α), and apoptosis-related proteins, such as cytochrome c (Cyt c), B cell lymphoma-2 (Bcl-2), Bcl-2 associated X protein (Bax), and cleaved caspase-3 were evaluated by western blot analysis. Cell apoptosis was analysed using annexin V/propidium iodide (PI) staining.

RESULTS

Treatment with CoCl2 significantly reduced H9c2 cell viability; the level of HIF-1α, which is a hypoxia-related indicator increased whereas the expression of SMN protein decreased. Hypoxia also induced cardiomyocyte apoptosis, indicated by reduced Bcl-2 expression and elevated cleaved caspase-3, Bax, and cytochrome c levels. Interestingly, SMN, which is a neuron protection factor, ameliorated CoCl2 -induced cell damage by reducing cardiomyocyte apoptosis through upregulation of Bcl-2 and inhibition of cytochrome c, cleaved caspase-3, and Bax expression.

CONCLUSION

Survival motor neuron prevents hypoxia-induced cell apoptosis through inhibition of the mitochondrial apoptotic pathway, and thereby exerts a protective effect on H9c2 cardiomyocytes.

Pum2-Mff axis fine-tunes mitochondrial quality control in acute ischemic kidney injury

Mitochondrial fission factor (Mff) has been demonstrated to play a role in the activation of mitochondrial cleavage and mitochondrial death, denoting its role in the regulation of mitochondrial quality control. Recent evidence suggested that the mRNA translation of Mff is under the negative regulation by the RNA-binding protein Pumilio2 (Pum2). This study was designed to examine the role of Pum2 and Mff in the governance of mitochondrial quality control in a murine model of acute ischemic kidney injury. Our results indicated that genetic deletion of Mff overtly attenuated ischemic acute kidney injury (AKI)-induced renal failure through inhibition of pro-inflammatory response, tubular oxidative stress, and ultimately cell death in the kidney. Furthermore, Mff inhibition effectively preserved mitochondrial homeostasis through amelioration of mitochondrial mitosis, restoration of Sirt1/3 expression, and boost of mitochondrial respiration. Western blot analysis revealed that levels of Pum2 were significantly downregulated by ischemic AKI, inversely coinciding with levels of Mff. Overexpression of Pum2 reduced ischemic AKI-mediated Mff upregulation and offered protection on renal tubules through modulation of mitochondrial quality control. Taken together, our data have unveiled the molecular mechanism of the Pum2-Mff axis in mitochondrial quality control in a mouse model of ischemic AKI. These data indicated the therapeutic potential of Pum2 activation and Mff inhibition in the management of ischemic AKI.

Identification of Hub Genes and Pathways in a Rat Model of Renal Ischemia-Reperfusion Injury Using Bioinformatics Analysis of the Gene Expression Omnibus (GEO) Dataset and Integration of Gene Expression Profiles

Background

This study aimed to identify hub genes and pathways in a rat model of renal ischemia-reperfusion injury (IRI) using bioinformatics analysis of the Gene Expression Omnibus (GEO) microarray dataset and integration of gene expression profiles.

Material/Methods

GEO software and the GEO2R calculation method were used to analyze two mRNA profiles, including GSE 39548 and GSE 108195. The co-expression of differentially expressed genes (DEGs) were identified and searched in the DAVID and STRING databases for pathway and protein-protein interaction (PPI) analysis. Cytoscape was used to draw the PPI network. DEGs were also analyzed using the Molecular Complex Detection (MCODE) algorithm. Cytoscape and cytoHubba were used to analyze the hub genes and visualize the molecular interaction networks. Rats (n=20) included the IRI model group (n=10) and a control group (n=10). Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used to measure and compare the expression of the identified genes in rat renal tissue in the IRI model and the control group.

Results

Ten hub genes were identified, STAT3, CD44, ITGAM, CCL2, TIMP1, MYC, THBS1, IGF1, SOCS3, and CD14. Apart from IGF1, qRT-PCR showed that expression of these genes was significantly increased in renal tissue in the rat model of IRI. The HIF-1α signaling pathway was involved in IRI in the rat model, which was supported by MCODE analysis.

Conclusions

In a rat model of renal IRI, bioinformatics analysis of the GEO dataset and integration of gene expression profiles identified involvement of HIF-1α signaling and the STAT3 hub gene.