Dysregulation of the axonal trafficking of nuclear‐encoded mitochondrial mRNA alters neuronal mitochondrial activity and mouse behavior

Hengst

2015

Neurotherapeutics

Localized protein synthesis is a mechanism by which morphologically polarized cells react in a spatially confined and temporally acute manner to changes in their environment. During the development of the nervous system intra-axonal protein synthesis is crucial for the establishment of neuronal connections. In contrast, mature axons have long been considered as translationally inactive but upon nerve injury or under neurodegenerative conditions specific subsets of mRNAs are recruited into axons and locally translated. Intra-axonally synthesized proteins can have pathogenic or restorative and regenerative functions, and thus targeting the axonal translatome might have therapeutic value, for example in the treatment of spinal cord injury or Alzheimer's disease. In the case of Alzheimer's disease the local synthesis of the stress response transcription factor activating transcription factor 4 mediates the long-range retrograde spread of pathology across the brain, and inhibition of local Atf4 translation downstream of the integrated stress response might interfere with this spread. Several molecular tools and approaches have been developed to target specifically the axonal translatome by either overexposing proteins locally in axons or, conversely, knocking down selectively axonally localized mRNAs. Many questions about axonal translation remain to be answered, especially with regard to the mechanisms establishing specificity but, nevertheless, targeting the axonal translatome is a promising novel avenue to pursue in the development for future therapies for various neurological conditions.

Section: Intra-axonal Protein Synthesismentioning

confidence: 87%

“…Thus, in theory, it might be sufficient to overexpress the entire the 3'UTR of an mRNA of interest in order to interfere with its localization or translation in axons. Indeed, such an approach has been followed successfully in genetically modified mice [27].…”

Section: Toolsmentioning

confidence: 99%

Targeting Axonal Protein Synthesis in Neuroregeneration and Degeneration

Hengst

2015

Neurotherapeutics

“…Several prior studies have demonstrated the importance of local translation for axon maintenance (Yoon et al, 2012), mitochondrial function (Kar et al, 2014) and survival (Cox et al, 2008), and suppression of local translation of lb2 mRNA causes neurodegeneration in vivo (Yoon et al, 2012). Here we report another dimension of local protein synthesis: in response to a physiologically relevant neurodegenerative stimulus axonal protein synthesis plays an active role in the transmission of neurodegeneration.…”

Section: Discussionmentioning

confidence: 99%

“…After the developmental period, the composition of the axonally localized transcriptome changes (Gumy et al, 2011), overall levels of mRNAs and ribosomes are lower (Kleiman et al, 1994), and mature axons have long been thought to be incapable of protein synthesis. However, recent evidence shows that protein synthesis persists in post-developmental CNS axons in vivo (Dubacq et al, 2009; Kar et al, 2014; Willis et al, 2011; Yoon et al, 2012). Additionally, upon injury of mature axons, a specific set of mRNAs and translation machinery are rapidly recruited into axons, and proteins are locally synthesized within mature axons (Rishal and Fainzilber, 2014).…”

Section: Introductionmentioning

confidence: 99%

Axonally Synthesized ATF4 Transmits a Neurodegenerative Signal across Brain Regions

Walker

Jean

et al. 2014

Cell

292

259

SUMMARY In Alzheimer’s disease (AD) brain exposure of axons to Aβ causes pathogenic changes that spread retrogradely by unknown mechanisms affecting the entire neuron. We found that locally applied Aβ1–42 initiates axonal synthesis of a defined set of proteins including the transcription factor ATF4. Inhibition of local translation and retrograde transport or knockdown of axonal Atf4 mRNA abolished Aβ-induced ATF4 transcriptional activity and cell loss. Aβ1–42 injection into the dentate gyrus (DG) of mice caused loss of forebrain neurons whose axons project to the DG. Protein synthesis and Atf4 mRNA were upregulated in these axons, and co-injection of Atf4 siRNA into the DG reduced the effects of Aβ1–42 in the forebrain. ATF4 protein and transcripts were found with greater frequency in axons in the brain of AD patients. These results reveal an active role for intra-axonal translation in neurodegeneration and identify ATF4 as a mediator for the spread of AD pathology.

“…Lamin b2 mRNA is localized to retinal axons in Xenopues laevis tadpoles and its depletion affects axon maintenance after axonal development 21 . Interference with the axonal transport of the mRNA encoding for cytochrome C oxidase IV alters mouse behavior 24 . Finally, Atf4 mRNA is found in adult axons of mice and human brains in the context of Aβ 1-42 -induced neurodegeneration 18 .…”

Section: Introductionmentioning

confidence: 99%

Detection of Axonally Localized mRNAs in Brain Sections Using High-Resolution <em>In Situ</em> Hybridization

Jean

Troy

et al. 2015

JoVE

AbstractmRNAs are frequently localized to vertebrate axons and their local translation is required for axon pathfinding or branching during development and for maintenance, repair or neurodegeneration in postdevelopmental periods. High throughput analyses have recently revealed that axons have a more dynamic and complex transcriptome than previously expected. These analysis, however have been mostly done in cultured neurons where axons can be isolated from the somato-dendritic compartments. It is virtually impossible to achieve such isolation in whole tissues in vivo. Thus, in order to verify the recruitment of mRNAs and their functional relevance in a whole animal, transcriptome analyses should ideally be combined with techniques that allow the visualization of mRNAs in situ. Recently, novel ISH technologies that detect RNAs at a singlemolecule level have been developed. This is especially important when analyzing the subcellular localization of mRNA, since localized RNAs are typically found at low levels. Here we describe two protocols for the detection of axonally-localized mRNAs using a novel ultrasensitive RNA ISH technology. We have combined RNAscope ISH with axonal counterstain using fluorescence immunohistochemistry or histological dyes to verify the recruitment of Atf4 mRNA to axons in vivo in the mature mouse and human brains. Video LinkThe video component of this article can be found at