The p38 MAP kinase pathway modulates the hypoxia response and glutamate receptor trafficking in aging neurons
- Rutgers The State University of New Jersey, United States
Figures
Figure 1 with 1 supplement
Signaling through PMK-1 p38 MAPK regulates GLR-1 AMPAR trafficking.
GLR-1::GFP fluorescence in (A) wild-type animals and (B) pmk-1(km25) mutants. GLR-1 is localized to elongated accumulations (indicated by yellow arrows). Bar: 5 μm. Average GLR-1::GFP number is quantified as (C, I) puncta or (D, J) accumulations per length of ventral cord dendrites. Average SNB-1::GFP puncta are quantified based on (E) number per length of ventral cord and (F) puncta width. (G) Relative glr-1 mRNA levels quantified by qRT-PCR and normalized to the mean value for wild type. (H) Spontaneous reversal frequency (number of reversals measured over a 5-min period) represented as a percentage of the mean value for wild type. Graph bar columns labeled with asterisks indicate statistical difference by ANOVA followed by Dunnett’s multiple comparison to wild type (****p<0.0001, ***p<0.001, **p<0.01, *p<0.05). Lines connecting specific columns indicate pairwise comparisons using the Holm-Šídák test. Error bars indicate SEM. N = 13–47 animals per genotype.
Figure 1—figure supplement 1
Additional related factors that do not Alter GLR-1 localization In C. elegans neurons.
(A–D) Average GLR-1::GFP number is quantified as (A, C) puncta or (B, E) accumulations per length of ventral cord dendrites. Graph bar columns labeled with asterisks indicate statistical difference by ANOVA followed by Dunnett’s multiple comparison to wild type (****p<0.0001). Error bars indicate SEM. N = 8–15 animals per genotype. (E–G) GLR-1::GFP fluorescence in wild-type animals that have been exposed to (A) OP50 E. coli, (B) 5 hr of Pseudomonas aeruginosa strain PA14, or (C) 8 hr of PA14. Bar: 5 μm.
Figure 2
The p38 MAPK pathway promotes GLR-1 AMPAR function and recycling from endosomes.
GLR-1::GFP fluorescence in (A) wild-type animals, (B) pmk-1(km25) mutants, and (C) pmk-1(km25) mutants containing a transgene that expresses dominant negative RAB-5 with a GDP-locked mutation. Yellow arrows indicate elongated accumulations. Bar: 5 μm. Average GLR-1::GFP number is quantified as (D) puncta or (E) accumulations per length of ventral cord dendrites. (F, J, N) GLR-1::GFP and (G, K, O) mRFP::SYX-7 fluorescence observed in the PVC neuron cell body of (F, G, H, I) wild type, (J, K, L, M) sek-1 mutants, and (N, O, P, Q) pmk-1 mutants. (H, L, P) Merged image of the red and green channels. (I, M, Q) Binary image with white indicating pixels with significant signal (colocalization) in both channels. (R) Fraction of GLR-1::GFP-labeled pixels that overlap with mRFP:SYX-7-labeled pixels. Graph bar columns labeled with asterisks indicate statistical difference by ANOVA followed by Dunnett’s multiple comparison to wild type (****p<0.0001, ***p<0.001, **p<0.01, *p<0.05). Lines connecting specific columns indicate pairwise comparisons using the Holm-Šídák test. Error bars indicate SEM. N = 13–16 animals per genotype.
Figure 3
Loss of p38 MAPK signaling occludes the effects of hypoxia on GLR-1 AMPAR trafficking.
GLR-1::GFP fluorescence in (A, B) wild-type animals or (C, D) pmk-1(km25) mutants under conditions of (A, C) normoxia or (B, D) hypoxia. Yellow arrows indicate elongated accumulations. Bar: 5 μm. Average GLR-1::GFP number is quantified as (E) puncta or (F) accumulations per length of ventral cord dendrites. (G, H) PMK-1::GFP fluorescence in wild-type animals under (G) normoxia or (H) hypoxia. Cell bodies for AVG and RIGL are indicated. Average nuclear PMK-1::GFP fluorescence intensity (normalized to the average value in wild type) is quantified in (I). Red bar columns indicate animals under normoxia, whereas blue bar columns indicate animals exposed to hypoxia. Graph bar columns labeled with asterisks (****p<0.0001, **p<0.01, *p<0.05) indicate statistical difference by (E, F) ANOVA followed by Dunnett’s multiple comparison to wild type or Tukey’s multiple comparison indicated by the brackets, and (I) Student t test. Error bars indicate SEM. N = 11–24 animals per genotype.
Figure 4
CDK-5 is required for p38 MAPK to regulate GLR-1 AMPAR trafficking.
GLR-1::GFP fluorescence in (A) wild-type animals, (B) pmk-1(km25) mutants, (C) cdk-5(ok626) mutants, and (D) pmk-1(km25) cdk-5(ok626) double mutants. Yellow arrows indicate elongated accumulations. Bar: 5 μm. Average GLR-1::GFP number is quantified as (E) puncta or (F) accumulations per length of ventral cord dendrites. (G) Spontaneous reversal frequency (number of reversals measured over a 5-min period) represented as a percentage of the mean value for wild type. Graph bar columns labeled with asterisks indicate statistical difference by ANOVA followed by Dunnett’s multiple comparison to wild type (****p<0.0001). Lines connecting specific columns indicate pairwise comparisons using the Holm-Šídák test. Error bars indicate SEM. N = 15–28 animals per genotype.
Figure 5
The PMK-1 p38 MAPK regulates LIN-10 localization.
LIN-10::GFP fluorescence in (A) wild-type animals, (B) pmk-1(km25) mutants, (C) cdk-5(ok626) mutants, and (D) pmk-1(km25) cdk-5(ok626) double mutants. Bar: 5 μm. (E) Average LIN-10::GFP puncta number is quantified per length of ventral cord dendrites. (F) Average integrated optical density (IOD) per puncta per animal as a measurement of total localized LIN-10::GFP. IOD is the sum of the pixel values for each puncta, reflecting both puncta size and fluorescence intensity. Graph bar columns labeled with asterisks indicate statistical difference by ANOVA followed by Dunnett’s multiple comparison to wild type (****p<0.0001, *p<0.05). Lines connecting specific columns indicate pairwise comparisons using the Holm-Šídák test. Error bars indicate SEM. N = 15 animals per genotype.
Figure 6
The PMK-1 p38 MAPK regulates EGL-9 localization.
EGL-9E::GFP fluorescence in (A) wild-type animals, (B) pmk-1(km25) mutants, (C) cdk-5(ok626) mutants, and (D) pmk-1(km25) cdk-5(ok626) double mutants. Bar: 5 μm. (E) Average EGL-9E::GFP puncta number is quantified per length of ventral cord dendrites. (F) Average integrated optical density (IOD) per puncta per animal as a measurement of total localized EGL-9E::GFP. IOD is the sum of the pixel values for each puncta, reflecting both puncta size and fluorescence intensity. Graph bar columns labeled with asterisks indicate statistical difference by ANOVA followed by Dunnett’s multiple comparison to wild type (****p<0.0001). Error bars indicate SEM. N = 13–20 animals per genotype.
Figure 7
The p38 MAPK pathway modulates the hypoxia response pathway.
Fluorescence from Venus expressed from the cysl-2 promoter in animals carrying a Pcysl-2::Venus transgene. Either (A, B) wild-type animals or (C, D) pmk-1(km25) mutants under (A, C) normoxia or (B, D) hypoxia are shown. Note that pharyngeal fluorescence is detected from the Pmyo-2::mCherry injection marker even under normoxia. Bar: 100 μm. (E) Relative nhr-57 mRNA levels from the indicated genotypes (under normoxia) quantified by qRT-PCR and normalized to the mean value for wild type. (F, G, H) Fluorescence from a HIF-1::GFP chimeric protein expressed from the glr-1 promoter in animals under normoxia and carrying a Pglr-1::HIF-1::GFP transgene. The PVC neuron cell body from (F) wild type, (G) egl-9(sa307) mutants, and (H) pmk-1(km25) mutants is shown. (I) Average relative HIF-1::GFP fluorescence levels (normalized to the mean value for wild type) observed in PVC nuclei under normoxia. Graph bar columns labeled with asterisks indicate statistical difference by ANOVA followed by Dunnett’s multiple comparison to wild type (****p<0.0001, ***p<0.001, **p<0.01). Error bars indicate SEM. N = 17–20 animals per genotype.
Figure 8
PMK-1 p38 MAPK activity declines with aAge.
(A) Western blot of whole animal lysates from the indicated genotype and developmental stage (either L4 larvae or adults aged 9 days past L4). Top panels show signal from anti-phospho-p38 MAPK antibody, whereas the bottom panels show signal from an anti-actin antibody. Arrows point to bands corresponding to the indicated protein. Asterisks indicate additional bands that cross react with the anti-phospho-p38 MAPK antibody but are not actually PMK-1 (i.e., they are not present in the pmk-1 molecular null mutant). The panels on the left and the panels on the right are from the same Western blot, but from different regions of the SDS-PAGE gel. (B) Quantification of the ratio of anti-phospho-p38 MAPK antibody signal to anti-actin antibody signal, normalized to the value of wild-type L4 animals. Values indicate an average from three independent Western blots. (C) Quantification of the ratio of pmk-1 mRNA to actin mRNA, normalized to the value of wild-type L4 animals. Values indicate an average from three independent qRT-PCR reactions. Graph bar columns labeled with asterisks indicate statistical significance by Student t test (*p<0.05). Error bars indicate SEM. (D, E, F, G) Fluorescence from GFP expressed from the T24B8.5 promoter in animals carrying a PT24B8.5::GFP transgene. Either (D, E) wild-type animals or (F, G) pmk-1(km25) mutants as (D, F) L4 stage larvae or (E, G) adults 9 days following the L4 stage are shown. Note that GFP expression from AIY (arrowheads) is from a transgenic marker (Pttx-3::GFP) incorporated into the array. Bar: 100 μm.
Figure 9
Age-onset downregulation of GLR-1 AMPARs through p38 MAPK and CDK-5 signaling.
GLR-1::GFP fluorescence in (A, B) wild-type animals, (C, D) cdk-5(ok626) mutants, and (E, F) wild-type animals expressing a wild-type pmk-1 cDNA from the glr-1 promoter (from a Pglr-1::PMK-1(+) transgene, labeled as pmk-1(OE) to indicate PMK-1 overexpression). Animals are either (A, C, E) L4 stage larvae or (B, D, F) adults aged 9 days past the L4 stage. Yellow arrows indicate elongated accumulations. Bar: 5 μm. Average GLR-1::GFP number is quantified as (G) puncta or (H) accumulations per length of ventral cord dendrites. Gray bar columns indicate L4 stage animals, whereas purple bar columns indicate older animals that are 9 days past the L4 stage. Graph bar columns labeled with asterisks indicate statistical difference by ANOVA followed by Dunnett’s multiple comparison to wild type (****p<0.0001, ***p<0.001). Lines connecting specific columns indicate pairwise comparisons using the Holm-Šídák test. Error bars indicate SEM. N = 13–18 animals per genotype. (I) Spontaneous reversal frequency (number of reversals measured over a 5-min period and normalized per minute) as measured at different days after the L4 stage in aging animals of the indicated genotype. Asterisks indicate statistical difference by ANOVA followed by Dunnett’s multiple comparison to wild type (*p<0.05) at the indicated time point.
Figure 10
Hypothetical model for p38 MAPK regulation of the hypoxia response pathway.
A hypothetical, step-by-step model of hypoxia response pathway interactions in C. elegans neurons is shown for conditions of either (A-D) normoxia or (E-H) hypoxia. (A) Under normoxia, oxygen binds to and activates EGL-9 (pink ovals). Oxygen also activates SEK-1 and PMK-1 (p38 MAPK, green and yellow ovals, respectively) through a mechanism that remains unknown. Activated p38 MAPK in turn phosphorylates one or more proteins (possible EGL-9 itself, as speculated in this cartoon with a ‘P’ in a yellow circle) that activate EGL-9 and trigger its recruitment to endosomes. Meanwhile, GLR-1 receptors (red channels) undergo continual endocytosis at the synapse. (B) Isoform EGL-9E, now bound to oxygen and possibly phosphorylated by p38 MAPK, becomes localized to endosomes, where it binds the PDZ-PTB domain protein LIN-10 (orange oval) and recruits it to endosomes by preventing its phosphorylation by the CDK-5 kinase (purple oval). (C) Once at endosomes, LIN-10 promotes the recycling of endocytosed GLR-1 AMPARs (red channels in the endosome) back to the synapse. (D) The final outcome is that GLR-1 synaptic levels are maintained. (E) Under hypoxia, lack of oxygen results in lower SEK-1/PMK-1 p38 MAPK activity and inactive EGL-9. (F) In the absence of oxygen, EGL-9E does not bind to LIN-10. This exposes the LIN-10 N-terminus (the localization domain of LIN-10) to CDK-5, which phosphorylates it, thereby inhibiting LIN-10 recruitment to endosomes. (G) Without endosomal LIN-10, GLR-1 AMPARs continue undergoing endocytosis from synapses but are not recycled, resulting in their accumulation in elongated endosomal compartments. (H) The final outcome is that GLR-1 synaptic levels become depleted.
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The p38 MAP kinase pathway modulates the hypoxia response and glutamate receptor trafficking in aging neurons
eLife 5:e12010.
https://doi.org/10.7554/eLife.12010
