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Death Associated Protein Kinase (DAPK) -mediated neurodegenerative mechanisms in nematode excitotoxicity.

Del Rosario JS, Feldmann KG, Ahmed T, Amjad U, Ko B, An J, Mahmud T, Salama M, Mei S, Asemota D, Mano I - BMC Neurosci (2015)

Bottom Line: However, the molecular mechanism by which DAPK exerts its effect is controversial.We further show that some proposed mechanisms of DAPK's action (modulation of synaptic strength, involvement of the DANGER-related protein MAB-21, and autophagy) do not have a major role in nematode excitotoxicity.Our studies highlight the prominence of DAPK and Pin1/PINN-1 as conserved mediators of cell death processes in diverse scenarios of neurodegeneration.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Pharmacology, and Neuroscience, Sophie Davis School of Biomedical Education (SBE), City College of New York (CCNY), The City University of New York (CUNY), New York, NY, USA. delrosariojohns@gmail.com.

ABSTRACT

Background: Excitotoxicity (the toxic overstimulation of neurons by the excitatory transmitter Glutamate) is a central process in widespread neurodegenerative conditions such as brain ischemia and chronic neurological diseases. Many mechanisms have been suggested to mediate excitotoxicity, but their significance across diverse excitotoxic scenarios remains unclear. Death Associated Protein Kinase (DAPK), a critical molecular switch that controls a range of key signaling and cell death pathways, has been suggested to have an important role in excitotoxicity. However, the molecular mechanism by which DAPK exerts its effect is controversial. A few distinct mechanisms have been suggested by single (sometimes contradicting) studies, and a larger array of potential mechanisms is implicated by the extensive interactome of DAPK.

Results: Here we analyze a well-characterized model of excitotoxicity in the nematode C. elegans to show that DAPK is an important mediator of excitotoxic neurodegeneration across a large evolutionary distance. We further show that some proposed mechanisms of DAPK's action (modulation of synaptic strength, involvement of the DANGER-related protein MAB-21, and autophagy) do not have a major role in nematode excitotoxicity. In contrast, Pin1/PINN-1 (a DAPK interaction-partner and a peptidyl-prolyl isomerase involved in chronic neurodegenerative conditions) suppresses neurodegeneration in our excitotoxicity model.

Conclusions: Our studies highlight the prominence of DAPK and Pin1/PINN-1 as conserved mediators of cell death processes in diverse scenarios of neurodegeneration.

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Related in: MedlinePlus

dapk-1 is an important mediator of nematode excitotoxicity. A) Dynamics of neurodegeneration in nematode excitotoxicity during development (using the glt-3;nuIs5 excitotoxicity model). dapk-1 ko mutation suppresses neurodegeneration in all developmental stages, but does not bring it down to background levels. B) Overexpression of wt dapk-1 from a heat-shock promoter enhances neurodegeneration compared to matched controls. In all bar graphs, error bars represent SE. Statistical significance is calculated using z score. *p < 0.05; ***p < 0.01.
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Fig1: dapk-1 is an important mediator of nematode excitotoxicity. A) Dynamics of neurodegeneration in nematode excitotoxicity during development (using the glt-3;nuIs5 excitotoxicity model). dapk-1 ko mutation suppresses neurodegeneration in all developmental stages, but does not bring it down to background levels. B) Overexpression of wt dapk-1 from a heat-shock promoter enhances neurodegeneration compared to matched controls. In all bar graphs, error bars represent SE. Statistical significance is calculated using z score. *p < 0.05; ***p < 0.01.

Mentions: To test the involvement of DAPK in nematode excitotoxicity we combined our excitotoxicity strain (glt-3;nuIs5) with a deletion allele of the nematode homolog of DAPK, dapk-1(gk219), a gene knockout that was used to confirm the effect of the (ubiquitously expressed) nematode DAPK in autophagy and innate immunity [42,45]. In our previously described model of neurodegeneration we use the sensitizing transgenic modification nuIs5, where hyperactive Gαs and GFP are expressed under the glr-1 promoter in ~30 neurons [39] and cause GluR-independent stochastic degeneration of ~1 of these at-risk neurons per animal. When we add the KO of the GluT gene glt-3 we observe that more of these at-risk neurons degenerate [37]. The GluT-KO-triggered exacerbated necrosis in glt-3;nuIs5 is GluR-dependent, and therefore qualifies as nematode excitotoxicity. Nematode excitotoxicity causes neuronal swelling and death that is manifested with characteristic kinetics as gradually and stochastically appearing vacuole-like structures in some of the at-risk postsynaptic neurons. These vacuole-like structures become more abundant during larval development as the Glu signaling system matures (usually reaching up to ~4.5 head neurons/animal at L3), and then decline due to removal of cell corpses by engulfment [37]. We now observe that adding dapk-1 ko to this excitotoxicity strain causes a strong and statistically significant suppression of neurodegeneration throughout development (Figure 1A, an additional independent cross gave very similar results, not shown). To further confirm the contribution of dapk-1 to nematode excitotoxicity, we overexpressed the wt dapk-1 cDNA from an extra-chromosomal transgenic construct under a heat-shock promoter [42]. Since heat-shock might affect susceptibility to neurodegeneration, we took special care to compare an exact match of treated animals, without or with the dapk-1 overexpression transgene. To that end we took advantage of the fact that the random and partial segregation of the non-integrated overexpression construct allows us to compare transgenic and non-transgenic animals on the same plate exposed to the same conditions. We observed that dapk-1 overexpression resulted in a strong and statistically significant potentiation of necrotic neurodegeneration in postsynaptic neurons in all developmental stages (Figure 1B). Together, our data indicate that DAPK is an important mediator of excitotoxicity in C. elegans, suggesting that diverse scenarios of excitotoxicity share a common mechanism that assigns a central role to DAPK.Figure 1


Death Associated Protein Kinase (DAPK) -mediated neurodegenerative mechanisms in nematode excitotoxicity.

Del Rosario JS, Feldmann KG, Ahmed T, Amjad U, Ko B, An J, Mahmud T, Salama M, Mei S, Asemota D, Mano I - BMC Neurosci (2015)

dapk-1 is an important mediator of nematode excitotoxicity. A) Dynamics of neurodegeneration in nematode excitotoxicity during development (using the glt-3;nuIs5 excitotoxicity model). dapk-1 ko mutation suppresses neurodegeneration in all developmental stages, but does not bring it down to background levels. B) Overexpression of wt dapk-1 from a heat-shock promoter enhances neurodegeneration compared to matched controls. In all bar graphs, error bars represent SE. Statistical significance is calculated using z score. *p < 0.05; ***p < 0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4414438&req=5

Fig1: dapk-1 is an important mediator of nematode excitotoxicity. A) Dynamics of neurodegeneration in nematode excitotoxicity during development (using the glt-3;nuIs5 excitotoxicity model). dapk-1 ko mutation suppresses neurodegeneration in all developmental stages, but does not bring it down to background levels. B) Overexpression of wt dapk-1 from a heat-shock promoter enhances neurodegeneration compared to matched controls. In all bar graphs, error bars represent SE. Statistical significance is calculated using z score. *p < 0.05; ***p < 0.01.
Mentions: To test the involvement of DAPK in nematode excitotoxicity we combined our excitotoxicity strain (glt-3;nuIs5) with a deletion allele of the nematode homolog of DAPK, dapk-1(gk219), a gene knockout that was used to confirm the effect of the (ubiquitously expressed) nematode DAPK in autophagy and innate immunity [42,45]. In our previously described model of neurodegeneration we use the sensitizing transgenic modification nuIs5, where hyperactive Gαs and GFP are expressed under the glr-1 promoter in ~30 neurons [39] and cause GluR-independent stochastic degeneration of ~1 of these at-risk neurons per animal. When we add the KO of the GluT gene glt-3 we observe that more of these at-risk neurons degenerate [37]. The GluT-KO-triggered exacerbated necrosis in glt-3;nuIs5 is GluR-dependent, and therefore qualifies as nematode excitotoxicity. Nematode excitotoxicity causes neuronal swelling and death that is manifested with characteristic kinetics as gradually and stochastically appearing vacuole-like structures in some of the at-risk postsynaptic neurons. These vacuole-like structures become more abundant during larval development as the Glu signaling system matures (usually reaching up to ~4.5 head neurons/animal at L3), and then decline due to removal of cell corpses by engulfment [37]. We now observe that adding dapk-1 ko to this excitotoxicity strain causes a strong and statistically significant suppression of neurodegeneration throughout development (Figure 1A, an additional independent cross gave very similar results, not shown). To further confirm the contribution of dapk-1 to nematode excitotoxicity, we overexpressed the wt dapk-1 cDNA from an extra-chromosomal transgenic construct under a heat-shock promoter [42]. Since heat-shock might affect susceptibility to neurodegeneration, we took special care to compare an exact match of treated animals, without or with the dapk-1 overexpression transgene. To that end we took advantage of the fact that the random and partial segregation of the non-integrated overexpression construct allows us to compare transgenic and non-transgenic animals on the same plate exposed to the same conditions. We observed that dapk-1 overexpression resulted in a strong and statistically significant potentiation of necrotic neurodegeneration in postsynaptic neurons in all developmental stages (Figure 1B). Together, our data indicate that DAPK is an important mediator of excitotoxicity in C. elegans, suggesting that diverse scenarios of excitotoxicity share a common mechanism that assigns a central role to DAPK.Figure 1

Bottom Line: However, the molecular mechanism by which DAPK exerts its effect is controversial.We further show that some proposed mechanisms of DAPK's action (modulation of synaptic strength, involvement of the DANGER-related protein MAB-21, and autophagy) do not have a major role in nematode excitotoxicity.Our studies highlight the prominence of DAPK and Pin1/PINN-1 as conserved mediators of cell death processes in diverse scenarios of neurodegeneration.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Pharmacology, and Neuroscience, Sophie Davis School of Biomedical Education (SBE), City College of New York (CCNY), The City University of New York (CUNY), New York, NY, USA. delrosariojohns@gmail.com.

ABSTRACT

Background: Excitotoxicity (the toxic overstimulation of neurons by the excitatory transmitter Glutamate) is a central process in widespread neurodegenerative conditions such as brain ischemia and chronic neurological diseases. Many mechanisms have been suggested to mediate excitotoxicity, but their significance across diverse excitotoxic scenarios remains unclear. Death Associated Protein Kinase (DAPK), a critical molecular switch that controls a range of key signaling and cell death pathways, has been suggested to have an important role in excitotoxicity. However, the molecular mechanism by which DAPK exerts its effect is controversial. A few distinct mechanisms have been suggested by single (sometimes contradicting) studies, and a larger array of potential mechanisms is implicated by the extensive interactome of DAPK.

Results: Here we analyze a well-characterized model of excitotoxicity in the nematode C. elegans to show that DAPK is an important mediator of excitotoxic neurodegeneration across a large evolutionary distance. We further show that some proposed mechanisms of DAPK's action (modulation of synaptic strength, involvement of the DANGER-related protein MAB-21, and autophagy) do not have a major role in nematode excitotoxicity. In contrast, Pin1/PINN-1 (a DAPK interaction-partner and a peptidyl-prolyl isomerase involved in chronic neurodegenerative conditions) suppresses neurodegeneration in our excitotoxicity model.

Conclusions: Our studies highlight the prominence of DAPK and Pin1/PINN-1 as conserved mediators of cell death processes in diverse scenarios of neurodegeneration.

Show MeSH
Related in: MedlinePlus