Septin 4, the drosophila ortholog of human CDCrel-1, accumulates in parkin mutant brains and is functionally related to the Nedd4 E3 ubiquitin ligase

Conservation and divergence of the G-interfaces of Drosophila melanogaster septins

Septins possess a conserved guanine nucleotide-binding (G) domain that participates in the stabilization of organized hetero-oligomeric complexes which assemble into filaments, rings and network-like structures. The fruit fly, Drosophila melanogaster, has five such septin genes encoding Sep1, Sep2, Sep4, Sep5 and Pnut. Here, we report the crystal structure of the heterodimer formed between the G-domains of Sep1 and Sep2, the first from an insect to be described to date. A G-interface stabilizes the dimer (in agreement with the expected arrangement for the Drosophila hexameric particle) and this bears significant resemblance to its human counterparts, even down to the level of individual amino acid interactions. On the other hand, a model for the G-interface formed between the two copies of Pnut which occupy the centre of the hexamer, shows important structural differences, including the loss of a highly favourable bifurcated salt-bridge network. Whereas wild-type Pnut purifies as a monomer, the reintroduction of the salt-bridge network results in stabilizing the dimeric interface in solution as shown by size exclusion chromatography and thermal stability measurements. Adaptive steered molecular dynamics reveals an unzipping mechanism for dimer dissociation which initiates at a point of electrostatic repulsion within the switch II region. Overall, the data contribute to a better understanding of the molecular interactions involved in septin assembly/disassembly.

LINC01588 regulates WWP2-mediated cardiomyocyte injury by interacting with HNRNPL

Cardiomyocyte dysfunction and apoptosis induced by ischemia-hypoxia are common features of many acute and chronic heart diseases. WW domain-containing E3 ubiquitin ligase (WWP2) has been identified as an important regulator in pathogenesis of some health-threatening diseases. Although a couple of recent reports prompted the potential role of WWP2 in heart dysfunction, however, its exact role and how its expression was regulated in ischemic-hypoxic cardiomyocytes are still elusive. Here, we found that WWP2 protein level was induced in anoxia/reoxygenation (A/R) treated cardiomyocytes in a time-dependent manner, accompanied by synchronous expression of LINC01588 and HNRNPL. Knockdown of LINC01588 increased cardiomyocyte apoptosis, the level of oxidative stress, and expression of pro-inflammatory cytokine genes, down-regulated the expression of WWP2 and promoted expression of SEPT4 gene that contributed to cardiomyocyte dysfunction and was a target gene of WWP2. LINC01588 overexpression improved the functions of A/R treated cardiomyocytes, up-regulated WWP2 and reduced SEPT4 expression. In the mechanism exploration, we found that LINC01588 could directly bind with HNRNPL protein that could interact with WWP2, suggesting that WWP2 was involved in the regulation of LINC01588 in A/R treated cardiomyocytes. Moreover, WWP2 inhibition declined the protective role of LINC01588 in cardiomyocyte dysfunction induced by A/R. Finally, we demonstrated that LINC01588 overexpression improved acute myocardial infarction in mice in vivo. In conclusion, LINC01588 improved A/R-induced cardiomyocyte dysfunction by interacting with HNRNPL and promoting WWP2-mediated degradation of SEPT4.

Peiminine Reduces ARTS-Mediated Degradation of XIAP by Modulating the PINK1/Parkin Pathway to Ameliorate 6-Hydroxydopamine Toxicity and α-Synuclein Accumulation in Parkinson's Disease Models In Vivo and In Vitro

Parkinson’s disease (PD) is a degenerative disease that can cause motor, cognitive, and behavioral disorders. The treatment strategies being developed are based on the typical pathologic features of PD, including the death of dopaminergic (DA) neurons in the substantia nigra of the midbrain and the accumulation of α-synuclein in neurons. Peiminine (PMN) is an extract of Fritillaria thunbergii Miq that has antioxidant and anti-neuroinflammatory effects. We used Caenorhabditis elegans and SH-SY5Y cell models of PD to evaluate the neuroprotective potential of PMN and address its corresponding mechanism of action. We found that pretreatment with PMN reduced reactive oxygen species production and DA neuron degeneration caused by exposure to 6-hydroxydopamine (6-OHDA), and therefore significantly improved the DA-mediated food-sensing behavior of 6-OHDA-exposed worms and prolonged their lifespan. PMN also diminished the accumulation of α-synuclein in transgenic worms and transfected cells. In our study of the mechanism of action, we found that PMN lessened ARTS-mediated degradation of X-linked inhibitor of apoptosis (XIAP) by enhancing the expression of PINK1/parkin. This led to reduced 6-OHDA-induced apoptosis, enhanced activity of the ubiquitin–proteasome system, and increased autophagy, which diminished the accumulation of α-synuclein. The use of small interfering RNA to down-regulate parkin reversed the benefits of PMN in the PD models. Our findings suggest PMN as a candidate compound worthy of further evaluation for the treatment of PD.

[Functional Characterization of Septin Complexes]

Septins belong to a family of conserved GTP-binding proteins found in majority of eukaryotic species except for higher plants. Septins form nonpolar complexes that further polymerize into filaments and associate with cell membranes, thus comprising newly acknowledged cytoskeletal system. Septins participate in a variety of cell processes and contribute to various pathophysiological states, including tumorigenesis and neurodegeneration. Here, we review the structural and functional properties of septins and the regulation of their dynamics with special emphasis on the role of septin filaments as a cytoskeletal system and its interaction with actin and microtubule cytoskeletons. We also discuss how septins compartmentalize the cell by forming local protein-anchoring scaffolds and by providing barriers for the lateral diffusion of the membrane proteins.

Septin4 as a novel binding partner of PARP1 contributes to oxidative stress induced human umbilical vein endothelial cells injure

Oxidative stress induced vascular endothelial cell injure is one of the key and initial event in the development of atherosclerosis. Septin4, as a member of GTP binding protein family, is widely expressed in the eukaryotic cells and considered to be an essential component of the cytoskeleton which is involved in many important physiological processes. However, whether Septin4 is involved in cardiovascular diseases, such as oxidative stress inducted endothelial cell injury still unclear. PARP1 as a DNA repair enzyme can be activated by identifying DNA damaged fragments, which consumes high levels of energy and leads to vascular endothelial cell apoptosis. Here, our results first found that Septin4 is involved in oxidative stress induced endothelial cell ROS production and apoptosis through knock-down and over-expression Septin4 approaches. Furthermore, to explore how Septin4 is involved in oxidative stress induced endothelial cells injure, we first identified that Septin4 is a novel PARP1 interacting protein and the interaction is enhanced under oxidative stress. In conclusions, our founding indicates that Septin4 is a novel essential factor involved in oxidative stress induced vascular endothelial cell injury by interacting with apoptosis-related protein PARP1.

Activation mechanisms of the E3 ubiquitin ligase parkin

Monogenetic, familial forms of Parkinson's disease (PD) only account for 5-10% of the total number of PD cases, but analysis of the genes involved therein is invaluable to understanding PD-associated neurodegenerative signaling. One such gene, parkin, encodes a 465 amino acid E3 ubiquitin ligase. Of late, there has been considerable interest in the role of parkin signaling in PD and in identifying its putative substrates, as well as the elucidation of the mechanisms through which parkin itself is activated. Its dysfunction underlies both inherited and idiopathic PD-associated neurodegeneration. Here, we review recent literature that provides a model of activation of parkin in the setting of mitochondrial damage that involves PINK1 (PTEN-induced kinase-1) and phosphoubiquitin. We note that neuronal parkin is primarily a cytosolic protein (with various non-mitochondrial functions), and discuss potential cytosolic parkin activation mechanisms.

Store-independent modulation of Ca(2+) entry through Orai by Septin 7

Orai channels are required for store-operated Ca²⁺ entry (SOCE) in multiple cell types. Septins are a class of GTP-binding proteins that function as diffusion barriers in cells. Here we show that Septin 7 acts as a ‘molecular brake’ on activation of Orai channels in Drosophila neurons. Lowering Septin 7 levels results in dOrai-mediated Ca²⁺ entry and higher cytosolic Ca²⁺ in resting neurons. This Ca²⁺ entry is independent of depletion of endoplasmic reticulum Ca²⁺ stores and Ca²⁺ release through the inositol-1,4,5-trisphosphate receptor. Importantly, store-independent Ca²⁺ entry through Orai compensates for reduced SOCE in the Drosophila flight circuit. Moreover, overexpression of Septin 7 reduces both SOCE and flight duration, supporting its role as a negative regulator of Orai channel function in vivo. Septin 7 levels in neurons can, therefore, alter neural circuit function by modulating Orai function and Ca²⁺ homeostasis.

Orai channels are well known to mediate store-operated calcium entry. Here authors show that in neurons of the Drosophila flight circuit, Septin 7 acts as a negative regulator of Orai channels, surprisingly, by modulating store-independent calcium entry through Orai.

Genome-wide scan of healthy human connectome discovers SPON1 gene variant influencing dementia severity

Aberrant connectivity is implicated in many neurological and psychiatric disorders, including Alzheimer's disease and schizophrenia. However, other than a few disease-associated candidate genes, we know little about the degree to which genetics play a role in the brain networks; we know even less about specific genes that influence brain connections. Twin and family-based studies can generate estimates of overall genetic influences on a trait, but genome-wide association scans (GWASs) can screen the genome for specific variants influencing the brain or risk for disease. To identify the heritability of various brain connections, we scanned healthy young adult twins with high-field, high-angular resolution diffusion MRI. We adapted GWASs to screen the brain's connectivity pattern, allowing us to discover genetic variants that affect the human brain's wiring. The association of connectivity with the SPON1 variant at rs2618516 on chromosome 11 (11p15.2) reached connectome-wide, genome-wide significance after stringent statistical corrections were enforced, and it was replicated in an independent subsample. rs2618516 was shown to affect brain structure in an elderly population with varying degrees of dementia. Older people who carried the connectivity variant had significantly milder clinical dementia scores and lower risk of Alzheimer's disease. As a posthoc analysis, we conducted GWASs on several organizational and topological network measures derived from the matrices to discover variants in and around genes associated with autism (MACROD2), development (NEDD4), and mental retardation (UBE2A) significantly associated with connectivity. Connectome-wide, genome-wide screening offers substantial promise to discover genes affecting brain connectivity and risk for brain diseases.