Axons in the mature central nervous system (CNS) fail to regenerate after axotomy, partly due to the inhibitory environment constituted by reactive glial cells producing astrocytic scars, chondroitin ...sulfate proteoglycans, and myelin debris. We investigated this inhibitory milieu, showing that it is reversible and depends on glial metabolic status. We show that glia can be reprogrammed to promote morphological and functional regeneration after CNS injury in Drosophila via increased glycolysis. This enhancement is mediated by the glia derived metabolites: L-lactate and L-2-hydroxyglutarate (L-2HG). Genetically/pharmacologically increasing or reducing their bioactivity promoted or impeded CNS axon regeneration. L-lactate and L-2HG from glia acted on neuronal metabotropic GABAB receptors to boost cAMP signaling. Local application of L-lactate to injured spinal cord promoted corticospinal tract axon regeneration, leading to behavioral recovery in adult mice. Our findings revealed a metabolic switch to circumvent the inhibition of glia while amplifying their beneficial effects for treating CNS injuries.
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•Activation of the PI3K and EGFR pathways in glia promotes CNS axon regeneration•Enhanced glial glycolysis mediates the induced axon regeneration via metabolites•L-lactate and L-2HG are sufficient to boost CNS axon regeneration•The metabolites act on neuronal GABAB receptors to elevate cAMP as inverse agonists
Li et al. reveal that the glial metabolic status is related to the failure of axon regeneration in the CNS. They show that the inhibitory environment can be essentially reversed by elevated aerobic glycolysis in glia, leading to axon regeneration in the CNS, which may be evolutionarily conserved.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Neurons exhibit a limited ability of repair. Given that mechanical forces affect neuronal outgrowth, it is important to investigate whether mechanosensitive ion channels may regulate axon ...regeneration. Here, we show that DmPiezo, a Ca2+-permeable non-selective cation channel, functions as an intrinsic inhibitor for axon regeneration in Drosophila. DmPiezo activation during axon regeneration induces local Ca2+ transients at the growth cone, leading to activation of nitric oxide synthase and the downstream cGMP kinase Foraging or PKG to restrict axon regrowth. Loss of DmPiezo enhances axon regeneration of sensory neurons in the peripheral and CNS. Conditional knockout of its mammalian homolog Piezo1 in vivo accelerates regeneration, while its pharmacological activation in vitro modestly reduces regeneration, suggesting the role of Piezo in inhibiting regeneration may be evolutionarily conserved. These findings provide a precedent for the involvement of mechanosensitive channels in axon regeneration and add a potential target for modulating nervous system repair.
•Piezo cell autonomously inhibits axon regeneration in Drosophila sensory neurons•Piezo channels are activated after axon injury or during axon regeneration•Piezo inhibits axon regeneration through calcium signaling, Nos, and PKG•Piezo1 also inhibits axon regeneration in mammals in vitro and in vivo
Piezo is a mechanosensitive ion channel that transduces mechanical stimuli into cellular responses. Here, Song et al. show that Piezo is recruited after axon injury to inhibit axon regeneration via the CamKII-Nos-PKG pathway, a process that may be evolutionarily conserved.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Atr is a serine/threonine kinase, known to sense single-stranded DNA breaks and activate the DNA damage checkpoint by phosphorylating Chek1, which inhibits Cdc25, causing cell cycle arrest. This ...pathway has not been implicated in neuroregeneration. We show that in Drosophila sensory neurons removing Atr or Chek1, or overexpressing Cdc25 promotes regeneration, whereas Atr or Chek1 overexpression, or Cdc25 knockdown impedes regeneration. Inhibiting the Atr-associated checkpoint complex in neurons promotes regeneration and improves synapse/behavioral recovery after CNS injury. Independent of DNA damage, Atr responds to the mechanical stimulus elicited during regeneration, via the mechanosensitive ion channel Piezo and its downstream NO signaling. Sensory neuron-specific knockout of Atr in adult mice, or pharmacological inhibition of Atr-Chek1 in mammalian neurons in vitro and in flies in vivo enhances regeneration. Our findings reveal the Piezo-Atr-Chek1-Cdc25 axis as an evolutionarily conserved inhibitory mechanism for regeneration, and identify potential therapeutic targets for treating nervous system trauma.
Infrared fluorescent proteins (IFPs) provide an additional color to GFP and its homologs in protein labeling. Drawing on structural analysis of the dimer interface, we identified a ...bacteriophytochrome in the sequence database that is monomeric in truncated form and engineered it into a naturally monomeric IFP (mIFP). We demonstrate that mIFP correctly labels proteins in live cells, Drosophila and zebrafish. It should be useful in molecular, cell and developmental biology.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
During developmental remodeling, neurites destined for pruning often degenerate on-site. Physical injury also induces degeneration of neurites distal to the injury site. Prompt clearance of ...degenerating neurites is important for maintaining tissue homeostasis and preventing inflammatory responses. Here we show that in both dendrite pruning and dendrite injury of Drosophila sensory neurons, epidermal cells rather than hemocytes are the primary phagocytes in clearing degenerating dendrites. Epidermal cells act via Draper-mediated recognition to facilitate dendrite degeneration and to engulf and degrade degenerating dendrites. Using multiple dendritic membrane markers to trace phagocytosis, we show that two members of the CD36 family, croquemort (crq) and debris buster (dsb), act at distinct stages of phagosome maturation for dendrite clearance. Our finding reveals the physiological importance of coordination between neurons and their surrounding epidermis, for both dendrite fragmentation and clearance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The enzymatic digestibility of alkali/peracetic acid (PAA)-pretreated bagasse was systematically investigated. The effects of initial solid consistency, cellulase loading and addition of supplemental
...β-glucosidase on the enzymatic conversion of glycan were studied. It was found the alkali–PAA pulp showed excellent enzymatic digestibility. The enzymatic glycan conversion could reach about 80% after 24
h incubation when enzyme loading was 10
FPU/g solid. Simultaneous saccharification and fermentation (SSF) results indicated that the pulp could be well converted to ethanol. Compared with dilute acid pretreated bagasse (DAPB), alkali–PAA pulp could obtain much higher ethanol and xylose concentrations. The fermentation broth still showed some cellulase activity so that the fed pulp could be further converted to sugars and ethanol. After the second batch SSF, the fermentation broth of alkali–PAA pulp still kept about 50% of initial cellulase activity. However, only 21% of initial cellulase activity was kept in the fermentation broth of DAPB. The xylose syrup obtained in SSF of alkali–PAA pulp could be well converted to 2,3-butanediol by
Klebsiella pneumoniae CGMCC 1.9131.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract
A neuron’s regenerative capacity is governed by its intrinsic and extrinsic environment. Both peripheral and central neurons exhibit cell-type-dependent axon regeneration, but the underlying ...mechanism is unclear. Glia provide a milieu essential for regeneration. However, the routes of glia-neuron signaling remain underexplored. Here, we show that regeneration specificity is determined by the axotomy-induced Ca
2+
transients only in the fly regenerative neurons, which is mediated by L-type calcium channels, constituting the core intrinsic machinery. Peripheral glia regulate axon regeneration via a three-layered and balanced modulation. Glia-derived tumor necrosis factor acts through its neuronal receptor to maintain calcium channel expression after injury. Glia sustain calcium channel opening by enhancing membrane hyperpolarization via the inwardly-rectifying potassium channel (Irk1). Glia also release adenosine which signals through neuronal adenosine receptor (AdoR) to activate HCN channels (Ih) and dampen Ca
2+
transients. Together, we identify a multifaceted glia-neuron coupling which can be hijacked to promote neural repair.
Neuroregeneration is a dynamic process synergizing the functional outcomes of multiple signaling circuits. Channelrhodopsin-based optogenetics shows the feasibility of stimulating neural repair but ...does not pin down specific signaling cascades. Here, we utilized optogenetic systems, optoRaf and optoAKT, to delineate the contribution of the ERK and AKT signaling pathways to neuroregeneration in live
larvae. We showed that optoRaf or optoAKT activation not only enhanced axon regeneration in both regeneration-competent and -incompetent sensory neurons in the peripheral nervous system but also allowed temporal tuning and proper guidance of axon regrowth. Furthermore, optoRaf and optoAKT differ in their signaling kinetics during regeneration, showing a gated versus graded response, respectively. Importantly in the central nervous system, their activation promotes axon regrowth and functional recovery of the thermonociceptive behavior. We conclude that non-neuronal optogenetics targets damaged neurons and signaling subcircuits, providing a novel strategy in the intervention of neural damage with improved precision.
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