Charge-transfer-driven ultrasensitive SERS sensing in a two-dimensional titanium carbonitride MXene.

Two-dimensional (2D) MXenes stand out as promising platforms for surface-enhanced Raman scattering (SERS) sensing owing to their metallic feature, various compositions, high surface area, compatibility with functionalization, and ease of fabrication. In this work, we report a high-performance 2D titanium carbonitride (Ti3CN) MXene SERS substrate. We reveal that the abundant electronic density of states near the Fermi level of Ti3CN MXene boosts the efficiency of photo-induced charge transfer at the interface of Ti3CN/molecule, resulting in significant Raman enhancement. The SERS sensitivity of Ti3CN MXene is further promoted through a 2D morphology regulation and molecular enrichment strategies. Moreover, prohibited drugs are detectable on this substrate, presenting the potential of trace-amount analysis on Ti3CN MXene. This work provides a deep insight of the SERS mechanisms of Ti3CN MXene and broadens the practical application of transition metal carbonitride MXene SERS substrates.

Two-dimensional MBenes with ordered metal vacancies for surface-enhanced Raman scattering.

As an emerging class of two-dimensional (2D) materials, MBenes show enormous potential for optoelectronic applications. However, their use in molecular sensing as surface-enhanced Raman scattering (SERS)-active material is unknown. Herein, for the first time, we develop a brand-new high-performance MBene SERS platform. Ordered vacancy-triggered highly sensitive SERS platform with outstanding signal uniformity based on a 2D Mo4/3B2 MBene material was designed. The 2D Mo4/3B2 MBene presented superior SERS activity to most of the semiconductor SERS substrates, showing a remarkable Raman enhancement factor of 3.88 × 106 and an ultralow detection limit of 1 × 10-9 M. The underlying SERS mechanism is revealed from systematic experiments and density functional theory calculations that the ultrahigh SERS sensitivity of 2D Mo4/3B2 MBene is derived from the efficient photoinduced charge transfer process between MBene substrates and adsorbed molecules. The abundant electronic density of states near the Fermi level of 2D Mo4/3B2 MBene enables its Raman enhancement by a factor of 100 000 times higher than that of the bulk MoB. Consequently, the 2D Mo4/3B2 MBene could accurately detect various trace chemical analytes. Moreover, with ordered metal vacancies in the 2D Mo4/3B2 MBene, uniform charge transfer sites are formed, resulting in an outstanding signal uniformity with a relative standard deviation down to 6.0%. This work opens up a new horizon for the high-performance SERS platform based on MBene materials, which holds great promise in the field of chemical sensing.

Smoothened is a therapeutic target for reducing glutamate toxicity in ischemic stroke.

Extracellular glutamate contributes to brain damage in ischemia. Under physiological conditions, glutamate transporters are responsible for regulating its intracellular/extracellular concentrations in the brain. However, how the extracellular glutamate is regulated in ischemia remains unclear. Here, we showed that the sonic hedgehog (SHH)­Smoothened (SMO)­GLT-1 pathway controlled extracellular glutamate and blocking SMO reduced ischemic brain damage in rodents. SHH was quickly released in a rodent model of ischemia, and activation of its pathway was associated with neuronal damage. Inhibiting SMO, the mediator of SHH signaling, maintained GLT-1 membrane expression, lowered extracellular glutamate, reduced infarct volume, and improved neurological functions in mice. Mechanistically, SHH suppressed GLT-1 membrane expression via PKCα phosphorylation of serine-562 on GLT-1. Last, administration of NVP-LDE225, an FDA-approved SMO antagonist used for cancer treatment in clinic, had protective effects in mice and cynomolgus monkeys subjected to ischemia. Together, these results suggest that SMO could be targeted for treating glutamate toxicity in ischemia.

Robo functions as an attractive cue for glial migration through SYG-1/Neph.

As one of the most-studied receptors, Robo plays functions in many biological processes, and its functions highly depend on Slit, the ligand of Robo. Here we uncover a Slit-independent role of Robo in glial migration and show that neurons can release an extracellular fragment of Robo upon cleavage to attract glia during migration in Caenorhabditis elegans. Furthermore, we identified the conserved cell adhesion molecule SYG-1/Neph as a receptor for the cleaved extracellular Robo fragment to mediate glial migration and SYG-1/Neph functions through regulation of the WAVE complex. Our studies reveal a previously unknown Slit-independent function and regulatory mechanism of Robo and show that the cleaved extracellular fragment of Robo can function as a ligand for SYG-1/Neph to guide glial migration. As Robo, the cleaved region of Robo, and SYG-1/Neph are all highly conserved across the animal kingdom, our findings may present a conserved Slit-independent Robo mechanism during brain development.

Sonic hedgehog induces GLT-1 degradation via PKC delta to suppress its transporter activities.

GLT-1 is mainly expressed in astrocytes and has a crucial role in glutamate uptake. Sonic hedgehog (SHH) can inhibit glutamate uptake and its pathway is activated in many brain diseases related with glutamate excitotoxicity. However, whether SHH regulates GLT-1 to affect glutamate uptake is not clear. Here, we use pharmacological and genetic methods to show that SHH induces GLT-1 degradation in astrocytes in a manner that is dependent on PKC delta (PKCδ) to regulate GLT-1 activities. GLT-1 protein levels are reduced as early as 2 hs in astrocytes after incubation with SHH, whereas its mRNA levels are not changed. This reduction is recapitulated when astrocytes are transfected with SmoA1, a constitutively active form of Smoothened (Smo), the mediator of SHH pathway. The reduction of GLT-1 and inhibition of aspartate current are not observed when staurosporine (STP) and BisindolylmaleimideII (BisII), agents known as PKC inhibitors, are present. Further, when PKCδ is knocked down in astrocytes, SHH cannot reduce GLT-1 protein levels. Therefore, SHH induces degradation of GLT-1 through PKCδ to regulate its activities.

TRPC6 expression in neurons is differentially regulated by NR2A- and NR2B-containing NMDA receptors.

The expression of transient receptor potential canonical 6 (TRPC6) in central nervous system (CNS) is important for neuronal functions and certain neural disorders. However, the regulatory mechanism of TRPC6 expression in neurons is still obscure. In this study, we show that TRPC6 expression in the primary cultured cortical neurons is bidirectionally regulated by glutamate. Activation of NR2A-containing NMDARs induces TRPC6 transcription through a calcineurin-dependent pathway. In contrast, activation of NR2B-containing NMDARs causes TRPC6 degradation through calpain. Thus, TRPC6 expression in neurons is regulated by glutamate in a bidirectional manner that is dependent on NR2A and NR2B.

RIP3 S-nitrosylation contributes to cerebral ischemic neuronal injury.

Cerebral ischemia-reperfusion is associated with NMDA receptor-mediated calcium influx which activates neuronal nitric oxide synthase (nNOS) and consequently induces NO production. NO S-nitrosylates cellular protein and aggravates neuronal injury. Receptor-interacting protein 3 (RIP3) is a sensor molecule regulating cell apoptosis and necrosis. However, the roles of RIP3 in cerebral ischemic injury remain elusive. In this study, we reported that RIP3 could be S-nitrosylated by the exogenous NO donor GSNO in HEK293 cells and the Cys(119) residue was the key nitrosylation site. In addition, we found that cerebral ischemia induced RIP3 S-nitrosylation at different time points of reperfusion, which was coupling with RIP3 phosphorylation (which is associated with its activation) and its interaction with receptor-interacting protein 1 (RIP1), and this process facilitated cerebral ischemic injury. Treatment with NMDA receptor antagonist MK801, or nNOS inhibitor 7NI, diminished RIP3 S-nitrosylation and reduced neuronal damage. Taken together, these data demonstrated that NMDAR-dependent RIP3 S-nitrosylation induced by ischemia facilitated its activation in the early stages of ischemia, blocking this process could reduce the ischemia neuronal injury.

N-methyl-D-aspartate receptor-dependent denitrosylation of neuronal nitric oxide synthase increase the enzyme activity.

Our laboratory once reported that neuronal nitric oxide synthase (nNOS) S-nitrosylation was decreased in rat hippocampus during cerebral ischemia-reperfusion, but the underlying mechanism was unclear. In this study, we show that nNOS activity is dynamically regulated by S-nitrosylation. We found that overexpressed nNOS in HEK293 (human embryonic kidney) cells could be S-nitrosylated by exogenous NO donor GSNO and which is associated with the enzyme activity decrease. Cys(331), one of the zinc-tetrathiolate cysteines, was identified as the key site of nNOS S-nitrosylation. In addition, we also found that nNOS is highly S-nitrosylated in resting rat hippocampal neurons and the enzyme undergos denitrosylation during the process of rat brain ischemia/reperfusion. Intrestingly, the process of nNOS denitrosylation is coupling with the decrease of nNOS phosphorylation at Ser(847), a site associated with nNOS activation. Further more, we document that nNOS denitrosylation could be suppressed by pretreatment of neurons with MK801, an antagonist of NMDAR, GSNO, EGTA, BAPTA, W-7, an inhibitor of calmodulin as well as TrxR1 antisense oligonucleotide (AS-ODN) respectively. Taken together, our data demonstrate that the denitrosylation of nNOS induced by calcium ion influx is a NMDAR-dependent process during the early stage of ischemia/reperfusion, which is majorly mediated by thioredoxin-1 (Trx1) system. nNOS dephosphorylation may be induced by the enzyme denitrosylation, which suggest that S-nitrosylation/denitrosylation of nNOS may be an important mechanism in regulating the enzyme activity.