Acetate ameliorates ovarian mitochondrial dysfunction in letrozole-induced polycystic ovarian syndrome rat model by improving mitofusin-2

Androgen excess and metabolic abnormality largely contribute to the pathogenesis of polycystic ovarian syndrome (PCOS), which primarily precipitates ovarian dysfunction and infertility in reproductive-age women. Impaired mitochondrial function and epigenetic alteration have been linked to the development of PCOS. However, it is unknown whether acetate would exert a therapeutic effect on ovarian mitochondrial dysfunction in PCOS. Herein, the study hypothesized that acetate reverses ovarian mitochondrial dysfunction in experimental PCOS rat model, possibly through modulation of mitofusin-2 (MFn2). Eight-week-old female Wistar rats were randomized into four groups (n = 5). Induction of PCOS was performed by 1 mg/kg letrozole (p.o.), administered for 21 days. Thereafter, the rats were treated with acetate (200 mg/kg; p.o.) for 6 weeks. The PCOS rats demonstrated androgen excess, multiple ovarian cysts, elevated anti-mullerian hormone and leptin and decreased SHBG, adiponectin and 17-β estradiol with corresponding increase in ovarian transforming growth factor-β1. Additionally, inflammation (tumor growth factor and nuclear factor-kB), elevated caspase-6, decreased hypoxia-inducible factor-1α and elevated histone deacetylase-2 (HDAC2) were observed in the ovaries of PCOS rats, while mitochondrial abnormality with evidence of decreased adenosine triphosphate synthase and MFn2 was observed in rats with PCOS. Treatment with acetate reversed the alterations. The present results collectively suggest that acetate ameliorates ovarian mitochondrial abnormality, a beneficial effect that is accompanied by MFn2 with consequent normalization of reproductive-endocrine profile and ovarian function. Perhaps, the present data provide hope for PCOS individuals that suffer infertility.

Mitofusin-2 induced by exercise modifies lipid droplet-mitochondria communication, promoting fatty acid oxidation in male mice with NAFLD

BACKGROUND AND AIM

The excessive accumulation of lipid droplets (LDs) is a defining characteristic of nonalcoholic fatty liver disease (NAFLD). The interaction between LDs and mitochondria is functionally important for lipid metabolism homeostasis. Exercise improves NAFLD, but it is not known if it has an effect on hepatic LD-mitochondria interactions. Here, we investigated the influence of exercise on LD-mitochondria interactions and its significance in the context of NAFLD.

APPROACH AND RESULTS

Mice were fed high-fat diet (HFD) or HFD-0.1 % methionine and choline-deficient diet (MCD) to emulate simple hepatic steatosis or non-alcoholic steatohepatitis, respectively. In both models, aerobic exercise decreased the size of LDs bound to mitochondria and the number of LD-mitochondria contacts. Analysis showed that the effects of exercise on HOMA-IR and liver triglyceride levels were independent of changes in body weight, and a positive correlation was observed between the number of LD-mitochondria contacts and NAFLD severity and with the lipid droplet size bound to mitochondria. Cellular fractionation studies revealed that ATP-coupled respiration and fatty acid oxidation (FAO) were greater in hepatic peridroplet mitochondria (PDM) from HFD-fed exercised mice than from equivalent sedentary mice. Finally, exercise increased FAO and mitofusin-2 abundance exclusively in PDM through a mechanism involving the curvature of mitochondrial membranes and the abundance of saturated lipids. Accordingly, hepatic mitofusin-2 ablation prevented exercise-induced FAO in PDM.

CONCLUSIONS

This study demonstrates that aerobic exercise has beneficial effects in murine NAFLD models by lessening the interactions between hepatic LDs and mitochondria, and by decreasing LD size, correlating with a reduced severity of NAFLD. Additionally, aerobic exercise increases FAO in PDM and this process is reliant on Mfn-2 enrichment, which modifies LD-mitochondria communication.

Zinc Overload Induces Damage to H9c2 Cardiomyocyte Through Mitochondrial Dysfunction and ROS-Mediated Mitophagy

Zinc homeostasis is essential for maintaining redox balance, cell proliferation, and apoptosis. However, excessive zinc exposure is toxic and leads to mitochondrial dysfunction. In this study, we established a zinc overload model by treating rat cardiomyocyte H9c2 cells with Zn2+ at different concentrations. Our results showed that zinc overload increased LDH and reactive oxygen species (ROS) levels, leading to cell death, mitochondrial membrane potential decrease and impaired mitochondrial function and dynamics. Furthermore, zinc overload activated the PINK1/Parkin signaling pathway and induced mitochondrial autophagy via ROS, while NAC inhibited mitophagy and weakened the activation of PINK1/Parkin pathway, thereby preserving mitochondrial biogenesis. In addition, our data also showed that Mfn2 deletion increased ROS production and exacerbated cytotoxicity induced by zinc overload. Our results therefore suggest that Zn2+-induced ROS generation causes mitochondrial autophagy and mitochondrial dysfunction, damaging H9c2 cardiomyocytes. Additionally, Mfn2 may play a key role in zinc ion-mediated endoplasmic reticulum and mitochondrial interactions. Our results provide a new perspective on zinc-induced toxicology.

In an experimental myocardial infarction model, L-arginine pre-intervention may exert cardioprotective effects by regulating OTULIN levels and mitochondrial dynamics

The experimental myocardial infarction (MI) model originating from isoproterenol (ISO) is frequently preferred in research due to its similarity to MI-induced damage in humans. Beneficial effects of L-arginine (L-Arg), a semi-essential amino acid, in cardiovascular diseases have been shown in many studies. This study was carried out to determine whether L-Arg pre-intervention has protective effects on heart tissue in the experimental MI model. The 28 rats used in the study were randomly divided into 4 equal groups: control, L-Arg, ISO, and L-Arg+ISO. Upon completion of all applications, cardiac markers in serum and biochemical, histopathological, and immunohistochemical examinations in cardiac tissues were performed. Cardiac markers, histopathological changes, oxidative stress, inflammation, and apoptosis were increased in the experimental MI model. In addition, administration of ISO deregulated OTULIN levels and mitochondrial dynamics in heart tissue. However, L-Arg pre-intervention showed a significant protective effect against changes in ISO-induced MI. L-Arg supplementation with cardioprotective effect may reduce the risks of possible pathophysiological processes in MI.

DNA Methylation-Mediated Mfn2 Gene Regulation in the Brain: A Role in Brain Trauma-Induced Mitochondrial Dysfunction and Memory Deficits

Repeated mild traumatic brain injuries (rMTBI) affect mitochondrial homeostasis in the brain. However, mechanisms of long-lasting neurobehavioral effects of rMTBI are largely unknown. Mitofusin 2 (Mfn2) is a critical component of tethering complexes in mitochondria-associated membranes (MAMs) and thereby plays a pivotal role in mitochondrial functions. Herein, we investigated the implications of DNA methylation in the Mfn2 gene regulation, and its consequences on mitochondrial dysfunction in the hippocampus after rMTBI. rMTBI dramatically reduced the mitochondrial mass, which was concomitant with decrease in Mfn2 mRNA and protein levels. DNA hypermethylation at the Mfn2 gene promoter was observed post 30 days of rMTBI. The treatment of 5-Azacytidine, a pan DNA methyltransferase inhibitor, normalized DNA methylation levels at Mfn2 promoter, which further resulted into restoration of Mfn2 function. The normalization of Mfn2 function was well correlated with recovery in memory deficits in rMTBI-exposed rats. Since, glutamate excitotoxicity serves as a primary insult after TBI, we employed in vitro model of glutamate excitotoxicity in human neuronal cell line SH-SY5Y to investigate the causal epigenetic mechanisms of Mfn2 gene regulation. The glutamate excitotoxicity reduced Mfn2 levels via DNA hypermethylation at Mfn2 promoter. Loss of Mfn2 caused significant surge in cellular and mitochondrial ROS levels with lowered mitochondrial membrane potential in cultured SH-SY5Y cells. Like rMTBI, these consequences of glutamate excitotoxicity were also prevented by 5-AzaC pre-treatment. Therefore, DNA methylation serves as a vital epigenetic mechanism involved in Mfn2 expression in the brain; and this Mfn2 gene regulation may play a pivotal role in rMTBI-induced persistent cognitive deficits. Closed head weight drop injury method was employed to induce repeated mild traumatic brain (rMTBI) in jury in adult, male Wistar rats. rMTBI causes hyper DNA methylation at the Mfn2 promoter and lowers the Mfn2 expression triggering mitochondrial dysfunction. However, the treatment of 5-azacytidine normalizes DNA methylation at the Mfn2 promoter and restores mitochondrial function.

Matrix metalloproteinase-2 proteolyzes mitofusin-2 and impairs mitochondrial function during myocardial ischemia-reperfusion injury

During myocardial ischemia and reperfusion (IR) injury matrix metalloproteinase-2 (MMP-2) is rapidly activated in response to oxidative stress. MMP-2 is a multifunctional protease that cleaves both extracellular and intracellular proteins. Oxidative stress also impairs mitochondrial function which is regulated by different proteins, including mitofusin-2 (Mfn-2), which is lost in IR injury. Oxidative stress and mitochondrial dysfunction trigger the NLRP3 inflammasome and the innate immune response which invokes the de novo expression of an N-terminal truncated isoform of MMP-2 (NTT-MMP-2) at or near mitochondria. We hypothesized that MMP-2 proteolyzes Mfn-2 during myocardial IR injury, impairing mitochondrial function and enhancing the inflammasome response. Isolated hearts from mice subjected to IR injury (30 min ischemia/40 min reperfusion) showed a significant reduction in left ventricular developed pressure (LVDP) compared to aerobically perfused hearts. IR injury increased MMP-2 activity as observed by gelatin zymography and increased degradation of troponin I, an intracellular MMP-2 target. MMP-2 preferring inhibitors, ARP-100 or ONO-4817, improved post-ischemic recovery of LVDP compared to vehicle perfused IR hearts. In muscle fibers isolated from IR hearts the rates of mitochondrial oxygen consumption and ATP production were impaired compared to those from aerobic hearts, whereas ARP-100 or ONO-4817 attenuated these reductions. IR hearts showed higher levels of NLRP3, cleaved caspase-1 and interleukin-1β in the cytosolic fraction, while the mitochondria-enriched fraction showed reduced levels of Mfn-2, compared to aerobic hearts. ARP-100 or ONO-4817 attenuated these changes. Co-immunoprecipitation showed that MMP-2 is associated with Mfn-2 in aerobic and IR hearts. ARP-100 or ONO-4817 also reduced infarct size and cell death in hearts subjected to 45 min ischemia/120 min reperfusion. Following myocardial IR injury, impaired contractile function and mitochondrial respiration and elevated inflammasome response could be attributed, at least in part, to MMP-2 activation, which targets and cleaves mitochondrial Mfn-2. Inhibition of MMP-2 activity protects against cardiac contractile dysfunction in IR injury in part by preserving Mfn-2 and suppressing inflammation.

Endothelial progenitor cell-derived exosomes inhibit pulmonary artery smooth muscle cell in vitro proliferation and resistance to apoptosis by modulating the Mitofusin-2 and Ras-Raf-ERK1/2 signaling pathway

Pulmonary arterial hypertension (PAH) mainly occurs as a result of abnormal proliferation and apoptosis resistance of pulmonary artery smooth muscle cells (PASMCs). Endothelial progenitor cell (EPC)-derived exosomes (Exos) (EPC-Exos) relieve PAH. However, there is still insufficient knowledge of whether EPC-Exos contribute to the pathological process of PAH, especially for PASMC repair. This study aimed to determine the effects of EPC-Exos on the proliferation, migration, and apoptosis of PASMCs and explore the possible underlying molecular mechanisms through bioinformatics analysis and in vitro testing. Bioinformatics analysis showed that the Ras signaling pathway and Exos were crucial in PAH. The PAH differential microRNAs (miRNAs) and miRNAs identified in EPC-Exos were intersected to obtain miR-21-5p. A target gene prediction program predicted mitofusin-2 (Mfn2) as a potential target of miR-21-5p. Cellular experiments demonstrated that EPC-Exos attenuated the viability, proliferation, migration, and apoptosis resistance of PASMCs under hypoxia. Mechanistically, EPC-Exos significantly upregulated Mfn2 expression and attenuated Ras-Raf-ERK1/2 signaling pathway activity. In conclusion, EPC-Exos suppress cell viability, proliferation, and migration and promote apoptosis in PASMCs under hypoxic conditions. It is possible to transport miR-21-5p to improve the expression of Mfn2 and inhibit the Ras-Raf-ERK1/2 signaling pathway directly or by targeting the expression of Mfn2. EPC-Exos are a potential therapeutic candidate for the treatment of PAH.

Mitofusin-2: Functional switch between mitochondrial function and neurodegeneration

Mitochondria are highly dynamic organelles known to play role in the regulation of several cellular biological processes. However, their dynamics such as number, shape, and biological functions are regulated by mitochondrial fusion and fission process. The balance between the fusion and fission process is most important for the maintenance of mitochondrial structure as well as cellular functions. The alterations within mitochondrial dynamic processes were found to be associated with the progression of neurodegenerative diseases. In recent years, mitofusin-2 (Mfn2), a GTPase has emerged as a multifunctional protein which not only is found to regulate the mitochondrial fusion-fission process but also known to regulate several cellular functions such as mitochondrial metabolism, cellular biogenesis, signalling, and apoptosis via maintaining the ER-mitochondria contact sites. In this review, we summarize the current knowledge of the structural and functional properties of the Mfn2, its transcriptional regulation and their roles in several cellular functions with a focus on current advances in the pathogenesis of neurodegenerative diseases.

Mitofusin-2 in cancer: Friend or foe?

Cancer is a category of disorders characterized by excessive cell proliferation with the ability to infiltrate or disseminate to other organs of the body. Mitochondrial dysfunction, as one of the most prominent hallmarks of cancer cells, has been related to the onset and development of various cancers. Mitofusin 2 (MFN2) is a major mediator of mitochondrial fusion, endoplasmic reticulum (ER)-mitochondria interaction, mitophagy and axonal transport of mitochondria. Available data have shown that MFN2, which its alterations have been associated with mitochondrial dysfunction, could affect cancer initiation and progression. In fact, it showed that MFN2 may have a double-edged sword effect on cancer fate. Precisely, it demonstrated that MFN2, as a tumor suppressor, induces cancer cell apoptosis and inhibits cell proliferation via Ca²⁺ and Bax-mediated apoptosis and increases P21 and p27 levels, respectively. It also could suppress cell survival via inhibiting PI3K/Akt, Ras-ERK1/2-cyclin D1 and mTORC2/Akt signaling pathways. On the other hand, MFN2, as an oncogene, could increase cancer invasion via snail-mediated epithelial-mesenchymal transition (EMT) and in vivo tumorigenesis. While remarkable progress has been achieved in recent decades, further exploration is required to elucidate whether MFN2 could be a friend or it's an enemy. This study aimed to highlight the different functions of MFN2 in various cancers.

Arsenic induces ferroptosis and acute lung injury through mtROS-mediated mitochondria-associated endoplasmic reticulum membrane dysfunction

The goal of this study was to analyze whether mitochondria-associated endoplasmic reticulum membrane (MAMs) dysfunction mediated arsenic (As)-evoked pulmonary ferroptosis and acute lung injury (ALI). As exposure led to alveolar structure damage, inflammatory cell infiltration and pulmonary function decline in mice. Ferritin, the marker of iron overload, was increased, GPX4, the index of lipid peroxidation, was decreased in As-exposed lungs and pulmonary epithelial cells (MLE-12). Pretreatment with ferrostatin-1 (Fer-1), the inhibitor of ferroptosis, alleviated As-evoked ALI. In addition, As-induced non-heme iron deposition was inhibited in Fer-1 pretreated-mice. Moreover, As-triggered mitochondria damage and ferroptosis were mitigated in Fer-1 pretreated-MLE-12 cells. Mechanistically, PERK phosphorylation and mitofusin-2 (Mfn-2) reduction was observed in As-exposed MLE-12 cells and mice lungs. Additionally, the interaction between PERK and Mfn-2 was downregulated and MAMs dysfunction was observed in As-exposed MLE-12 cells. Intriguingly, PERK inhibitor and Mfn-2-overexpression all mitigated As-induced ferroptosis in MLE-12 cells. Additionally, CLPP and mtHSP70, the markers of mitochondrial stress, were upregulated, mitochondrial ROS (mtROS) was elevated, mitochondrial membrane potential (MMP) and ATP were decreased in As-exposed MLE-12 cells. Mitoquinone mesylate (MitoQ), a novel mitochondrial-targeted antioxidant, alleviated As-induced excess mtROS, mitochondrial stress, MAMs dysfunction in pulmonary epithelial cells. Similarly, in vivo experiments indicated that MitoQ pretreatment countered As-induced pulmonary ferroptosis and ALI. These data indicated that mtROS-initiated MAMs dysfunction is, at least partially, implicated in As-evoked ferroptosis and ALI.

MFN2 knockdown promotes osteogenic differentiation of iPSC-MSCs through aerobic glycolysis mediated by the Wnt/β-catenin signaling pathway

Background

Mitofusin-2 (MFN2) is a kind of GTPase that participates in the regulation of mitochondrial fusion, which is related to a variety of physiological and pathological processes, including energy metabolism, cell differentiation, and embryonic development. However, it remains unclear whether MFN2 is involved in the metabolism and osteogenic differentiation of mesenchymal stem cells (MSCs).

Methods

MFN2 knockdown (MFN2-KD) and MFN2-overexpressing (MFN2-OE) induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs) were constructed by lentivirus. The commercial kits were utilized to detect the glycolysis and oxidative phosphorylation (OXPHOS) rate. Flow cytometry, Western blot, quantitative real-time polymerase chain reaction (qRT-PCR), RNA-seq, immunofluorescence, and immunoprecipitation were employed for phenotype and molecular mechanism assessment.

Results

We demonstrated that MFN2 and Wnt/β-catenin signaling pathway regulated glycolysis of iPSC-MSCs. The lack of MFN2 promoted the osteogenic differentiation of iPSC-MSCs, and aerobic glycolysis in the presence of sufficient oxygen, which increased glucose consumption and lactic acid production, as well as the glycolytic enzyme activity and gene expression. Inhibiting the Wnt/β-catenin signaling pathway normalized the enhanced glycolytic rate and osteogenic differentiation of MFN2-KD iPSC-MSCs. MFN2-OE iPSC-MSCs displayed the opposite phenotype.

Conclusions

Downregulating MFN2 promotes osteogenic differentiation of iPSC-MSCs through aerobic glycolysis mediated by the Wnt/β-catenin signaling pathway. Our research reveals the new function of MFN2 in regulating the osteogenic differentiation and energy metabolism of MSCs, which will provide a new therapeutic target and theoretical basis for alveolar bone repair and periodontal regenerative treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02836-w.

Mitofusin 2, a key coordinator between mitochondrial dynamics and innate immunity

Remodeling of mitochondrial dynamics and mitochondrial morphology plays a pivotal role in the maintenance of mitochondrial homeostasis in response to pathogenic attacks or stress stimuli. In addition to their role in metabolism and energy production, mitochondria participate in diverse biological functions, including innate immune responses driven by macrophages in response to infections or inflammatory stimuli. Mitofusin-2 (MFN2), a mitochondria-shaping protein regulating mitochondrial fusion and fission, plays a crucial role in linking mitochondrial function and innate immune responses. In this article, we review the role of MFN2 in the regulation of innate immune responses during viral and bacterial infections. We also summarize the current knowledge on the role of MFN2 in coordinating inflammatory, atherogenic, and fibrotic responses. MFN2-mediated crosstalk between mitochondrial dynamics and innate immune responses may determine the outcomes of pathogenic infections.

Restored microRNA-326-5p Inhibits Neuronal Apoptosis and Attenuates Mitochondrial Damage via Suppressing STAT3 in Cerebral Ischemia/Reperfusion Injury

Studies have greatly explored the role of microRNAs (miRNAs) in cerebral ischemia/reperfusion injury (CI/RI). But the specific mechanism of miR-326-5p in CI/RI is still elusive. Hence, this study was to unmask the mechanism of miR-326-5p/signal transducer and activator of transcription-3 (STAT3) axis in CI/RI. Two models (oxygen and glucose deprivation [OGD] in primary rat cortical neurons and middle cerebral artery occlusion [MCAO] in Sprague-Dawley rats) were established to mimic CI/RI in vitro and in vivo, respectively. Loss- and gain-of function assays were performed with OGD-treated neurons and with MCAO rats. Afterward, viability, apoptosis, oxidative stress and mitochondrial membrane potential in OGD-treated neurons were tested, as well as pathological changes, apoptosis and mitochondrial membrane potential in brain tissues of MCAO rats. Mitofusin-2 (Mfn2), miR-326-5p and STAT3 expression in OGD-treated neurons and in brain tissues of MCAO rats were detected. Mfn2 and miR-326-5p were reduced, and STAT3 was elevated in OGD-treated neurons and brain tissues of MCAO rats. miR-326-5p targeted and negatively regulated STAT3 expression. Restoring miR-326-5p or reducing STAT3 reinforced viability, inhibited apoptosis and oxidative stress, increased mitochondrial membrane potential and increased Mfn2 expression in OGD-treated neurons. Up-regulating miR-326-5p or down-regulating STAT3 relieved pathological changes, inhibited apoptosis and elevated mitochondrial membrane potential and Mfn2 expression in brain tissues of rats with MCAO. This study elucidates that up-regulated miR-326-5p or down-regulated STAT3 protects against CI/RI by elevating Mfn2 expression.

Effect of photobiomodulation on mitochondrial dynamics in peripheral nervous system in streptozotocin-induced type 1 diabetes in rats

There is no effective treatment to halt peripheral nervous system damage in diabetic peripheral neuropathy. Mitochondria have been at the center of discussions as important factors in the development of neuropathy in diabetes. Photobiomodulation has been gaining clinical acceptance as it shows beneficial effects on a variety of nervous system disorders. In this study, the effects of photobiomodulation (904 nm, 45 mW, 6.23 J/cm², 0.13 cm², 60 ns pulsed time) on mitochondrial dynamics were evaluated in an adult male rat experimental model of streptozotocin-induced type 1 diabetes. Results presented here indicate that photobiomodulation could have an important role in preventing or reversing mitochondrial dynamics dysfunction in the course of peripheral nervous system damage in diabetic peripheral neuropathy. Photobiomodulation showed its effects on modulating the protein expression of mitofusin 2 and dynamin-related protein 1 in the sciatic nerve and in the dorsal root ganglia neurons of streptozotocin-induced type 1 diabetes in rats.

Regulation of MFN2 by berberine alleviates obesity exacerbated colitis

Obesity has become a global health issue, which can cause metabolic abnormalities systemically leading to increased morbidity of series diseases. At present, researches have presented obesity is a high-risk factor for colitis, and berberine shows positive therapeutic effect on colitis. Thus, we explored the beneficial effects and potential mechanisms of berberine on obesity-exacerbated colitis in this article. High-fat diet (HFD) exacerbated dextran sulfate sodium (DSS) induced colitis mice model was applied, the results showed that HFD promoted DSS-induced weight loss and inflammatory manifestations in intestine. The results of cytokines in serum and mRNA expression of inflammatory indicators in colon showed that HFD increased all their levels evidently, and the outcomes of Western blot analyses presented that HFD downregulated the MFN2 expression, inhibited the phosphorylation of AMPK as well as upregulated the BIP/Grp78 expression, while berberine could significantly reverse all these situations. In vitro, we stimulated Caco-2 cells with palmitic acid (PA) to replicate the lipotoxicity damage in the intestine, and the results presented that intervention therapy of berberine effectively enhanced the MFN2 expression, inhibited the mRNA levels of inflammatory factors, and reversed the PA induced protein level changes of AMPK and BIP/Grp78. In general, we proposed that berberine could regulate MFN2 to alleviate obesity exacerbated colitis.

Inhibition of the proteasome preserves Mitofusin-2 and mitochondrial integrity, protecting cardiomyocytes during ischemia-reperfusion injury

Cardiomyocyte loss is the main cause of myocardial dysfunction following an ischemia-reperfusion (IR) injury. Mitochondrial dysfunction and altered mitochondrial network dynamics play central roles in cardiomyocyte death. Proteasome inhibition is cardioprotective in the setting of IR; however, the mechanisms underlying this protection are not well-understood. Several proteins that regulate mitochondrial dynamics and energy metabolism, including Mitofusin-2 (Mfn2), are degraded by the proteasome. The aim of this study was to evaluate whether proteasome inhibition can protect cardiomyocytes from IR damage by maintaining Mfn2 levels and preserving mitochondrial network integrity. Using ex vivo Langendorff-perfused rat hearts and in vitro neonatal rat ventricular myocytes, we showed that the proteasome inhibitor MG132 reduced IR-induced cardiomyocyte death. Moreover, MG132 preserved mitochondrial mass, prevented mitochondrial network fragmentation, and abolished IR-induced reductions in Mfn2 levels in heart tissue and cultured cardiomyocytes. Interestingly, Mfn2 overexpression also prevented cardiomyocyte death. This effect was apparently specific to Mfn2, as overexpression of Miro1, another protein implicated in mitochondrial dynamics, did not confer the same protection. Our results suggest that proteasome inhibition protects cardiomyocytes from IR damage. This effect could be partly mediated by preservation of Mfn2 and therefore mitochondrial integrity.

MiR-195 regulates mitochondrial function by targeting mitofusin-2 in breast cancer cells

Mitochondrial dynamics is a highly dysregulated process in cancer. Apoptosis and mitochondrial fission are two concurrent events wherein increased mitochondrial fragmentation serves as a hallmark of apoptosis. We have shown earlier that miR-195 exerts pro-apoptotic effects in breast cancer cells. Herein, we have demonstrated miR-195 as a modulator of mitochondrial dynamics and function. Imaging experiments upon miR-195 treatment have shown that mitochondria undergo extensive fission. We validated mitofusin2 as a potential target of miR-195. This may provide a molecular explanation for the respiratory defects induced by miR-195 over-expression in breast cancer cells. Active, but not total, mitochondrial mass, was reduced with increasing levels of miR-195. We have further shown that miR-195 enhances mitochondrial SOD-2 expression but does not affect PINK1 levels in breast cancer cells. Collectively, we have revealed that miR-195 is a modulator of mitochondrial dynamics by targeting MFN2 thereby impairing mitochondrial function. Concomitantly, it enhances the scavenger of reactive oxygen species (SOD-2) to maintain moderate levels of oxidative stress. Our findings suggest a therapeutic potential of miR-195 in both ER-positive as well as ER-negative breast cancer cells.

Mitofusin-2 acts as biomarker for predicting poor prognosis in hepatitis B virus related hepatocellular carcinoma

OBJECTIVE

To investigate the expression of Mitofusin-2 (MFN2) in HCC tissues and its role in the development of HCC.

METHODS

A total of 107 HCC specimens were collected for tissue microarray analysis and immunohistochemistry (IHC) analysis. The relationship between MFN2 expression and clinical features of patients with HCC was analyzed.

RESULTS

Expression level of MFN2 in HCC tissues was 0.92 ± 0.78, significantly lower than that of matched paracancerous liver tissues (1.25 ± 0.75). Patients with low expression of MFN2 had significantly higher rates of cirrhosis than those with high expression of MFN2 (P = 0.049). Kaplan-Meier survival analysis showed that HCC patients with low expression of MFN2 had a worse prognosis in overall survival than HCC patients with high expression of MFN2 (P = 0.027). Patients with high expression of MFN2 had a better prognosis in disease-free survival compared with HCC patients with low expression of MFN2 (P = 0.047). Vascular invasion and MFN2 expression were shown to be prognostic variables for overall survival in patients with HCC. Multivariate analysis showed that vascular invasion (P < 0.001) and MFN2 expression (P = 0.045) were independent prognostic factors for overall survival. Vascular invasion (P < 0.001) and MFN2 expression (P = 0.042) were independent risk factors associated with disease-free survival.

CONCLUSION

Our data revealed that MFN2 expression was decreased in HCC samples. High MFN2 expression was correlated with longer survival times in patients with HCC and served as an independent factor for better outcomes. Our study therefore provides a promising biomarker for the prognostic prediction of HCC and a potential therapeutic target for the disease.

Low expression of MFN2 is associated with early unexplained miscarriage by regulating autophagy of trophoblast cells

INTRODUCTION

Miscarriage is a common complication during pregnancy. Mitofusin-2 (MFN2) deficiency in trophoblastic cells is reported to be an important cause for early miscarriage. MFN2 can regulate mitochondrial autophagy, although the mechanisms remain unknown. This study aims to investigate the roles of MFN2 and autophagy in early unexplained miscarriage.

METHODS

Immunohistochemistry and western blotting were used to detect the MFN2 expression in villous tissues from women who had early unexplained miscarriage. Western blotting was used to detect the expression of autophagy-related proteins (ATG5, BECLIN1, and LC3), MMP-2, MMP-9, and integrin β1. Immunofluorescence was used to detect the expression of autophagosome after transfection with GFP-LC3. We used JC-1 to measure the mitochondrial membrane potential and transmission electron microscopy (TEM) to observe the ultrastructure of mitochondria. The levels of β-hCG and progesterone in the trophoblast were determined by the chemiluminescence method.

RESULTS

Immunofluorescence analysis demonstrated that MFN2 in the villous tissues of women with early unexplained miscarriage was significantly lower than that of women in the normal pregnancy group. Increased levels of LC3, ATG5, and BECLIN1 were observed by western blotting. After transfection with MFN2-siRNA, the level of MFN2 decreased, whereas LC3, ATG5, and BECLIN1 levels increased significantly in the trophoblasts. More autophagosomes and significant impairment of mitochondrial function were observed by TEM. The levels of β-hCG, progesterone, MMP-2, MMP-9, and integrin β1 were significantly reduced in the MFN2-siRNA group.

CONCLUSION

Low expression of MFN2 leads to mitochondrial dysfunction, increased level of autophagy, and trophoblast cell dysfunction, which could be accounted for early unexplained miscarriage.

Tying trafficking to fusion and fission at the mighty mitochondria

The mitochondrion is a unique organelle that serves as the main site of ATP generation needed for energy in the cell. However, mitochondria also play essential roles in cell death through apoptosis and necrosis, as well as a variety of crucial functions related to stress regulation, autophagy, lipid synthesis and calcium storage. There is a growing appreciation that mitochondrial function is regulated by the dynamics of its membrane fusion and fission; longer, fused mitochondria are optimal for ATP generation, whereas fission of mitochondria facilitates mitophagy and cell division. Despite the significance of mitochondrial homeostasis for such crucial cellular events, the intricate regulation of mitochondrial fusion and fission is only partially understood. Until very recently, only a single mitochondrial fission protein had been identified. Moreover, only now have researchers turned to address the upstream machinery that regulates mitochondrial fusion and fission proteins. Herein, we review the known GTPases involved in mitochondrial fusion and fission, but also highlight recent studies that address the mechanisms by which these GTPases are regulated. In particular, we draw attention to a substantial new body of literature linking endocytic regulatory proteins, such as the retromer VPS35 cargo selection complex subunit, to mitochondrial homeostasis. These recent studies suggest that relationships and cross-regulation between endocytic and mitochondrial pathways may be more widespread than previously assumed.

Estrogen-related receptor α is essential for maintaining mitochondrial integrity in cisplatin-induced acute kidney injury

Acute kidney injury (AKI) has been associated with not only higher in-hospital mortality but also the subsequent development of chronic kidney disease (CKD). Recent evidence has suggested the involvement of mitochondrial dysfunction and impaired dynamics in the pathogenesis of AKI. Estrogen-related receptor α (ERRα) is an orphan nuclear receptor that acts as a transcription factor to regulate the transcription of genes required for mitochondrial biogenesis and oxidative phosphorylation. In the present study, we examined the effects of ERRα deficiency on the progression of AKI induced by cisplatin. Male C57BL/6 J wild-type and ERRα-/- mice received a single intraperitoneal injection of 20 mg/kg cisplatin. Seventy-two hours after the injection, kidney function and morphology were evaluated. ERRα expression was observed in renal tubules, and cisplatin inhibited its translocation into nuclei. ERRα deficiency exacerbated cisplatin-induced renal dysfunction and tubular injury, as well as oxidative stress and apoptosis. ERRα-/- mice kidneys revealed lower mitochondrial DNA content and swollen mitochondria with reduced cristae. In addition, these mice had lower expression of the mitochondrial fusion protein mitofusin-2. The cisplatin-induced decrease in mitochondrial DNA and altered mitochondrial structure were more severe in ERRα-/- mice. In cultured mouse proximal tubular epithelial cells, the ERRα inverse agonist XCT-790 significantly inhibited mitofusin-2 expression and induced mitochondrial fragmentation. Taken together, our findings suggest the involvement of ERRα in the progression of cisplatin-induced AKI probably through impaired mitochondrial dynamics.

Mitofusin-2 mediated mitochondrial Ca2+ uptake 1/2 induced liver injury in rat remote ischemic perconditioning liver transplantation and alpha mouse liver-12 hypoxia cell line models

AIM

To investigate the protective mechanism of mitofusin-2 (Mfn2) in rat remote ischemic perconditioning (RIC) models and revalidate it in alpha mouse liver-12 (AML-12) hypoxia cell lines.

METHODS

Sprague-Dawley rats were divided into three groups (n = 6 each): sham, orthotopic liver transplantation and RIC. After operation, blood samples were collected to test alanine aminotransferase and aspartate aminotransferase. The liver lobes were harvested for histopathological examination, western blotting (WB) and quantitative real-time (qRT)-PCR. AML-12 cell lines were then subjected to normal culture, anoxic incubator tank culture (hypoxia) and anoxic incubator tank culture with Mfn2 knockdown (hypoxia + Si), and data of qRT-PCR, WB, mitochondrial membrane potential (ΔΨm), apoptosis, endoplasmic reticulum Ca²⁺ concentrations and mitochondrial Ca²⁺ concentrations were collected.

RESULTS

Both sham and normal culture groups showed no injury during the experiment. The RIC group showed amelioration of liver function compared with the orthotopic liver transplantation group (P < 0.05). qRT-PCR and WB confirmed that Mfn2-mitochondrial Ca²⁺ uptake 1/2 (MICUs) axis was changed (P < 0.005). In AML-12 cell lines, compared with the hypoxia group, the hypoxia + Si group attenuated the collapse of ΔΨm and apoptosis (P < 0.005). The endoplasmic reticulum Ca²⁺ decrease and mitochondrial Ca²⁺ overloading observed in the hypoxia group were also attenuated in the hypoxia + Si group (P < 0.005). Finally, qRT-PCR and WB confirmed the Mfn2-MICUs axis change in all the groups (P < 0.005).

CONCLUSION

Mfn2 participates in liver injury in rat RIC models and AML-12 hypoxia cell lines by regulating the MICUs pathway.

MicroRNA-214 Affects Fibroblast Differentiation of Adipose-Derived Mesenchymal Stem Cells by Targeting Mitofusin-2 during Pelvic Floor Dysfunction in SD Rats with Birth Trauma

BACKGROUND/AIMS

This study investigated whether microRNA-214 (miR-214) targets mitofusin-2 (Mfn2) in the process of fibroblast differentiation of adipose-derived mesenchymal stem cells (ADMSCs) during pelvic floor dysfunction (PFD) in Sprague Dawley (SD) rats with birth trauma.

METHODS

The ADMSCs were isolated from 4-6 week male SD rats (n = 20) and were cultured and divided into the blank, miR-214 mimic negative control (NC), miR-214 mimic, miR-214 inhibitor NC, miR-214 inhibitor, empty vector, Mfn2 over-expression and miR-214 + Mfn2 over-expression groups. Fibroblast differentiation of ADMSCs was measured with immunocytochemistry and immunofluorescence methods. The expression of miR-214 and the mRNA and protein expression of Mfn2, FSP1, Collagen I, Collagen III, Elastin, LOX, Fibulin-5, PPAR-γ and Runx2 were detected using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting, respectively. A dual-luciferase reporter assay was performed to confirm whether Mfn2 was the target gene of miR-214.

RESULTS

During ADMSC differentiation into fibroblasts, miR-214 expression was up-regulated, but the expression of Mfn2 was down-regulated. Fibroblast differentiation of ADMSCs was promoted in the miR-214 mimic group but was inhibited in the miR-214 inhibitor and Mfn2 over-expression groups. The expression of Mfn2 was decreased, but the expression of FSP1, Collagen I, Collagen III, Elastin, LOX, Fibulin-5, PPAR-γ or Runx2 was increased in the miR-214 mimic group; the miR-214 inhibitor group and Mfn2 over-expression group exhibited the opposite results. Mfn2 was the target gene of miR-214.

CONCLUSIONS

The study provided strong evidence that miR-214 could promote fibroblast differentiation of ADMSCs by down-regulating Mfn2 to improve PFD in SD rats with birth trauma.

Exogenous H2S regulates endoplasmic reticulum-mitochondria cross-talk to inhibit apoptotic pathways in STZ-induced type I diabetes

The upregulation of reactive oxygen species (ROS) is a primary cause of cardiomyocyte apoptosis in diabetes cardiomyopathy (DCM). Mitofusin-2 (Mfn-2) is a key protein that bridges the mitochondria and endoplasmic reticulum (ER). Hydrogen sulfide (H₂S)-mediated cardioprotection is related to antioxidant effects. The present study demonstrated that H₂S inhibited the interaction between the ER and mitochondrial apoptotic pathway. This study investigated cardiac function, ultrastructural changes in the ER and mitochondria, apoptotic rate using TUNEL, and the expression of ER stress-associated proteins and mitochondrial apoptotic proteins in cardiac tissues in STZ-induced type I diabetic rats treated with or without NaHS (donor of H₂S). Mitochondria of cardiac tissues were isolated, and MPTP opening and cytochrome c (cyt C) and Mfn-2 expression were also detected. Our data showed that hyperglycemia decreased the cardiac function by ultrasound cardiogram, and the administration of exogenous H₂S ameliorated these changes. We demonstrated that the expression of ER stress sensors and apoptotic rates were elevated in cardiac tissue of DCM and cultured H9C2 cells, but the expression of these proteins was reduced following exogenous H₂S treatment. The expression of mitochondrial apoptotic proteins, cyt C, and mPTP opening was decreased following treatment with exogenous H₂S. In our experiment, the expression and immunofluorescence of Mfn-2 were both decreased after transfection with Mfn-2-siRNA. Hyperglycemia stimulated ER interactions and mitochondrial apoptotic pathways, which were inhibited by exogenous H₂S treatment through the regulation of Mfn-2 expression.

Mitofusin-2 knockdown increases ER-mitochondria contact and decreases amyloid β-peptide production

Mitochondria are physically and biochemically in contact with other organelles including the endoplasmic reticulum (ER). Such contacts are formed between mitochondria‐associated ER membranes (MAM), specialized subregions of ER, and the outer mitochondrial membrane (OMM). We have previously shown increased expression of MAM‐associated proteins and enhanced ER to mitochondria Ca²⁺ transfer from ER to mitochondria in Alzheimer's disease (AD) and amyloid β‐peptide (Aβ)‐related neuronal models. Here, we report that siRNA knockdown of mitofusin‐2 (Mfn2), a protein that is involved in the tethering of ER and mitochondria, leads to increased contact between the two organelles. Cells depleted in Mfn2 showed increased Ca²⁺ transfer from ER to mitchondria and longer stretches of ER forming contacts with OMM. Interestingly, increased contact resulted in decreased concentrations of intra‐ and extracellular Aβ₄₀ and Aβ₄₂. Analysis of γ‐secretase protein expression, maturation and activity revealed that the low Aβ concentrations were a result of impaired γ‐secretase complex function. Amyloid‐β precursor protein (APP), β‐site APP‐cleaving enzyme 1 and neprilysin expression as well as neprilysin activity were not affected by Mfn2 siRNA treatment. In summary, our data shows that modulation of ER–mitochondria contact affects γ‐secretase activity and Aβ generation. Increased ER–mitochondria contact results in lower γ‐secretase activity suggesting a new mechanism by which Aβ generation can be controlled.

GLP-1 promotes mitochondrial metabolism in vascular smooth muscle cells by enhancing endoplasmic reticulum-mitochondria coupling

Incretin GLP-1 has important metabolic effects on several tissues, mainly through the regulation of glucose uptake and usage. One mechanism for increasing cell metabolism is modulating endoplasmic reticulum (ER)-mitochondria communication, as it allows for a more efficient transfer of Ca(2+) into the mitochondria, thereby increasing activity. Control of glucose metabolism is essential for proper vascular smooth muscle cell (VSMC) function. GLP-1 has been shown to produce varied metabolic actions, but whether it regulates glucose metabolism in VSMC remains unknown. In this report, we show that GLP-1 increases mitochondrial activity in the aortic cell line A7r5 by increasing ER-mitochondria coupling. GLP-1 increases intracellular glucose and diminishes glucose uptake without altering glycogen content. ATP, mitochondrial potential and oxygen consumption increase at 3h of GLP-1 treatment, paralleled by increased Ca(2+) transfer from the ER to the mitochondria. Furthermore, GLP-1 increases levels of Mitofusin-2 (Mfn2), an ER-mitochondria tethering protein, via a PKA-dependent mechanism. Accordingly, PKA inhibition and Mfn2 down-regulation prevented mitochondrial Ca(2+) increases in GLP-1 treated cells. Inhibiting both Ca(2+) release from the ER and Ca(2+) entry into mitochondria as well as diminishing Mfn2 levels blunted the increase in mitochondrial activity in response to GLP-1. Altogether, these results strongly suggest that GLP-1 increases ER-mitochondria communication in VSMC, resulting in higher mitochondrial activity.

Altered mitochondrial biogenesis and its fusion gene expression is involved in the high-altitude adaptation of rat lung

Intermittent hypobaric hypoxia-induced preconditioning (IHH-PC) of rat favored the adaption of lungs to severe HH conditions, possibly through stabilization of mitochondrial function. This is based on the data generated on regulatory coordination of nuclear DNA-encoded mitochondrial biogenesis; dynamics, and mitochondrial DNA (mtDNA)-encoded oxidative phosphorylation (mtOXPHOS) genes expression. At 16th day after start of IHH-PC (equivalent to 5000m, 6h/d, 2w of treatment), rats were exposed to severe HH stimulation at 9142m for 6h. The IHH-PC significantly counteracted the HH-induced effect of increased lung: water content; tissue damage; and oxidant injury. Further, IHH-PC significantly increased the mitochondrial number, mtDNA content and mtOXPHOS complex activity in the lung tissues. This observation is due to an increased expression of genes involved in mitochondrial biogenesis (PGC-1α, ERRα, NRF1, NRF2 and TFAM), fusion (Mfn1 and Mfn2) and mtOXPHOS. Thus, the regulatory pathway formed by PGC-1α/ERRα/Mfn2 axes is required for the mitochondrial adaptation provoked by IHH-PC regimen to counteract subsequent HH stress.

MicroRNA-106b induces mitochondrial dysfunction and insulin resistance in C2C12 myotubes by targeting mitofusin-2

MicroRNA-106b (miR-106b) is reported to correlate closely with skeletal muscle insulin resistance and type 2 diabetes. The aim of this study was to identify an mRNA targeted by miR-106b which regulates skeletal muscle insulin sensitivity. MiR-106b was found to target the 3' untranslated region (3' UTR) of mitofusin-2 (Mfn2) through miR-106b binding sites and to downregulate Mfn2 protein abundance at the post-transcriptional level by luciferase activity assay combined with mutational analysis and immunoblotting. Overexpression of miR-106b resulted in mitochondrial dysfunction and insulin resistance in C2C12 myotubes. MiR-106b was increased in insulin-resistant cultured C2C12 myotubes induced by TNF-α, and accompanied by increasing Mfn2 level, miR-106b loss of function improved mitochondrial function and insulin sensitivity impaired by TNF-α in C2C12 myotubes. In addition, both overexpression and downregulation of miR-106b upregulated peroxisome proliferator-activated receptor gamma coactivator (PGC)-1α and estrogen-related receptor (ERR)-α expression. MiR-106b targeted Mfn2 and regulated skeletal muscle mitochondrial function and insulin sensitivity. Therefor, Inhibition of miR-106b may be a potential new strategy for treating insulin resistance and type 2 diabetes.

A novel 5'-uncoding region -1248 A>G variation of mitofusin-2 gene is associated with hypertension in Chinese

PURPOSE

Mitofusin2 gene (Mfn2, also named Hyperplasia suppressive gene, HSG) is very important in the origin and development of hypertension. However, the mechanism of Mfn2/HSG expression regulation was not uncovered. This study was designed to explore the association of a novel 5'-uncoding region (UCR) -1248 A>G variation of HSG/Mfn2 gene and hypertension.

MATERIALS AND METHODS

472 healthy, normotensive subjects [normotension (NT) group], 454 prehypertensive subjects [prehypertension (PH) group] and 978 hypertensive patients [essential hypertension (EH) group] were screened for an association study between 5'-UCR -1248 A>G of Mfn2/HSG and hypertension by polymerase chain reaction and DNA sequencing after venous blood was drawn and DNA was extracted.

RESULTS

When comparing the A and G frequency in EH, PH and NT groups, in total, NT group significantly had higher A frequency than in PH group [odds ratio (OR)=1.605, confidence interval (CI) 95%=1.063-2.242, p=0.025] and EH group (OR=5.395, CI 95%=3.783-7.695, p<0.01). When subgrouped by gender, A frequency in NT group was still significantly higher than in EH group (male: OR= 4.264, CI 95%=2.780-6.543, p<0.01; female: OR=8.897, CI 95%=4.686-16.891, p<0.01), but not from PH group, either in male group or in female group. Ordinal Logistic Regression analysis showed that A>G variation was significantly related with blood pressure level (B=-1.271, Wald=40.914, CI 95%=-1.660 - -0.881, p<0.01).

CONCLUSION

5'-UCR -1248 A>G variation of Mfn2/HSG gene was a novel variation and may be associated with hypertension in Chinese.

Mitofusin-2 ameliorates high-fat diet-induced insulin resistance in liver of rats

AIM: To investigate the effects of mitofusin-2 (MFN2) on insulin sensitivity and its potential targets in the liver of rats fed with a high-fat diet (HFD).

METHODS: Rats were fed with a control or HFD for 4 or 8 wk, and were then infected with a control or an MFN2 expressing adenovirus once a week for 3 wk starting from the 9^th wk. Blood glucose (BG), plasma insulin and insulin sensitivity of rats were determined at end of the 4^th and 8^th wk, and after treatment with different amounts of MFN2 expressing adenovirus (10⁸, 10⁹ or 10¹⁰ vp/kg body weight). BG levels were measured by Accu-chek Active Meter. Plasma insulin levels were analyzed by using a Rat insulin enzyme-linked immunosorbent assay kit. Insulin resistance was evaluated by measuring the glucose infusion rate (GIR) using a hyperinsulinemic euglycemic clamp technique. The expression or phosphorylation levels of MFN2 and essential molecules in the insulin signaling pathway, such as insulin receptor (INSR), insulin receptor substrate 2 (IRS2), phosphoinositide-3-kinase (PI3K), protein kinase beta (AKT2) and glucose transporter type 2 (GLUT2) was assayed by quantitative real-time polymerase chain reaction and Western-blotting.

RESULTS: After the end of 8 wk, the body weight of rats receiving the normal control diet (ND) and the HFD was not significantly different (P > 0.05). Compared with the ND group, GIR in the HFD group was significantly decreased (P < 0.01), while the levels of BG, triglycerides (TG), total cholesterol (TC) and insulin in the HFD group were significantly higher than those in the ND group (P < 0.05). Expression of MFN2 mRNA and protein in liver of rats was significantly down-regulated in the HFD group (P < 0.01) after 8 wk of HFD feeding. The expression of INSR, IRS2 and GLUT2 were down-regulated markedly (P < 0.01). Although there were no changes in PI3K-P85 and AKT2 expression, their phosphorylation levels were decreased significantly (P < 0.01). After intervention with MFN2 expressing adenovirus for 3 wk, the expression of MFN2 mRNA and protein levels were up-regulated (P < 0.01). There was no difference in body weight of rats between the groups. The levels of BG, TG, TC and insulin in rats were lower than those in the Ad group (P < 0.05), but GIR in rats infected with Ad-MFN2 was significantly increased (P < 0.01), compared with the Ad group. The expression of INSR, IRS2 and GLUT2 was increased, while phosphorylation levels of PI3K-P85 and AKT2 were increased (P < 0.01), compared with the Ad group.

CONCLUSION: HFDs induce insulin resistance, and this can be reversed by MFN2 over-expression targeting the insulin signaling pathway.

Subacute peripheral and optic neuropathy syndrome with no evidence of a toxic or nutritional cause

BACKGROUND

The syndrome of subacute simultaneous peripheral neuropathy and bilateral optic neuropathy is known to occur in tropical countries, probably due to malnutrition or toxicity, but not often seen in developed countries. We report seven patients in London who were not malnourished or alcoholic, and in whom no clear cause was found.

METHODS

We retrospectively reviewed the case notes and arranged some further investigations.

RESULTS

All patients developed peripheral and bilateral optic neuropathy within 6 months. Patients were aged 30-52, and all of Jamaican birth and race but lived in the UK. Most had subacute, painful ataxic sensory axonal neuropathy or neuronopathy, some with myelopathy. Nerve conduction studies revealed minor demyelinating features in two cases. The optic neuropathy was symmetrical, subacute and monophasic, usually with marked reduction in visual acuity. CSF protein concentration was usually elevated but other laboratory investigations were normal. Patients showed only modest improvement at follow-up.

CONCLUSION

These patients share a common clinical and electrophysiological phenotype, age, ethnicity and elevated CSF protein, but otherwise normal laboratory investigations. The syndrome is a cause of significant morbidity in young people. The cause remains uncertain despite thorough investigation.