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Sustained activation of Akt elicits mitochondrial dysfunction to block Plasmodium falciparum infection in the mosquito host.

Luckhart S, Giulivi C, Drexler AL, Antonova-Koch Y, Sakaguchi D, Napoli E, Wong S, Price MS, Eigenheer R, Phinney BS, Pakpour N, Pietri JE, Cheung K, Georgis M, Riehle M - PLoS Pathog. (2013)

Bottom Line: Despite an apparent increase in mitochondrial biogenesis in young females (3 d), energy deficiencies were apparent as decreased oxidative phosphorylation and increased [AMP]/[ATP] ratios.Hence, Akt-induced changes in mitochondrial dynamics perturb midgut homeostasis to enhance parasite resistance and decrease mosquito infective lifespan.Further, quality control of mitochondrial function in the midgut is necessary for the maintenance of midgut health as reflected in energy homeostasis and tissue repair and renewal.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Microbiology and Immunology, School of Medicine, University of California, Davis, Davis, California, United States of America. sluckhart@ucdavis.edu

ABSTRACT
The overexpression of activated, myristoylated Akt in the midgut of female transgenic Anopheles stephensi results in resistance to infection with the human malaria parasite Plasmodium falciparum but also decreased lifespan. In the present study, the understanding of mitochondria-dependent midgut homeostasis has been expanded to explain this apparent paradox in an insect of major medical importance. Given that Akt signaling is essential for cell growth and survival, we hypothesized that sustained Akt activation in the mosquito midgut would alter the balance of critical pathways that control mitochondrial dynamics to enhance parasite killing at some cost to survivorship. Toxic reactive oxygen and nitrogen species (RNOS) rise to high levels in the midgut after blood feeding, due to a combination of high NO production and a decline in FOXO-dependent antioxidants. Despite an apparent increase in mitochondrial biogenesis in young females (3 d), energy deficiencies were apparent as decreased oxidative phosphorylation and increased [AMP]/[ATP] ratios. In addition, mitochondrial mass was lower and accompanied by the presence of stalled autophagosomes in the posterior midgut, a critical site for blood digestion and stem cell-mediated epithelial maintenance and repair, and by functional degradation of the epithelial barrier. By 18 d, the age at which An. stephensi would transmit P. falciparum to human hosts, mitochondrial dysfunction coupled to Akt-mediated repression of autophagy/mitophagy was more evident and midgut epithelial structure was markedly compromised. Inhibition of RNOS by co-feeding of the nitric-oxide synthase inhibitor L-NAME at infection abrogated Akt-dependent killing of P. falciparum that begins within 18 h of infection in 3-5 d old mosquitoes. Hence, Akt-induced changes in mitochondrial dynamics perturb midgut homeostasis to enhance parasite resistance and decrease mosquito infective lifespan. Further, quality control of mitochondrial function in the midgut is necessary for the maintenance of midgut health as reflected in energy homeostasis and tissue repair and renewal.

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Over-expression of myrAkt was associated with reduced MAP kinase activation in the An. stephensi midgut.Midguts from 3–5 day old female HM myrAkt and NTG An. stephensi were dissected at 0.5 h post blood feeding and processed for western blot. Data are represented as the average fold change ± SEM of phospho-protein levels for pERK, p-p38, and p-JNK quantified by densitometry and normalized first to GAPDH to control for protein loading differences and then to phospho-protein levels in NTG controls. Data collected from 6–8 separate cohorts of A. stephensi were analyzed by Student's t-test (alpha = 0.05). P values are noted on the graph.
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ppat-1003180-g001: Over-expression of myrAkt was associated with reduced MAP kinase activation in the An. stephensi midgut.Midguts from 3–5 day old female HM myrAkt and NTG An. stephensi were dissected at 0.5 h post blood feeding and processed for western blot. Data are represented as the average fold change ± SEM of phospho-protein levels for pERK, p-p38, and p-JNK quantified by densitometry and normalized first to GAPDH to control for protein loading differences and then to phospho-protein levels in NTG controls. Data collected from 6–8 separate cohorts of A. stephensi were analyzed by Student's t-test (alpha = 0.05). P values are noted on the graph.

Mentions: The upregulation of cytoskeletal proteins associated with the progression of autophagy and mitophagy suggested some involvement of these processes in the phenotype of myrAkt An. stephensi. To address this hypothesis, we examined activation levels (phosphorylation) of autophagy-promoting ERK, JNK, and p38 MAPK in the midguts of 3–5 d old, age-matched NTG and HM An. stephensi. Activation levels of all three MAPKs were reduced in the midgut of HM females relative to NTG females (by 40–60%; Fig. 1), which in the context of Akt overexpression, suggested a state of disruption of normal, autophagic repair processes in the midgut epithelium. Together with our LC-MS/MS data, these data suggested that proteins associated with mitochondria and maintenance of the structure of the midgut were altered by tissue-specific Akt overexpression in An. stephensi.


Sustained activation of Akt elicits mitochondrial dysfunction to block Plasmodium falciparum infection in the mosquito host.

Luckhart S, Giulivi C, Drexler AL, Antonova-Koch Y, Sakaguchi D, Napoli E, Wong S, Price MS, Eigenheer R, Phinney BS, Pakpour N, Pietri JE, Cheung K, Georgis M, Riehle M - PLoS Pathog. (2013)

Over-expression of myrAkt was associated with reduced MAP kinase activation in the An. stephensi midgut.Midguts from 3–5 day old female HM myrAkt and NTG An. stephensi were dissected at 0.5 h post blood feeding and processed for western blot. Data are represented as the average fold change ± SEM of phospho-protein levels for pERK, p-p38, and p-JNK quantified by densitometry and normalized first to GAPDH to control for protein loading differences and then to phospho-protein levels in NTG controls. Data collected from 6–8 separate cohorts of A. stephensi were analyzed by Student's t-test (alpha = 0.05). P values are noted on the graph.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585164&req=5

ppat-1003180-g001: Over-expression of myrAkt was associated with reduced MAP kinase activation in the An. stephensi midgut.Midguts from 3–5 day old female HM myrAkt and NTG An. stephensi were dissected at 0.5 h post blood feeding and processed for western blot. Data are represented as the average fold change ± SEM of phospho-protein levels for pERK, p-p38, and p-JNK quantified by densitometry and normalized first to GAPDH to control for protein loading differences and then to phospho-protein levels in NTG controls. Data collected from 6–8 separate cohorts of A. stephensi were analyzed by Student's t-test (alpha = 0.05). P values are noted on the graph.
Mentions: The upregulation of cytoskeletal proteins associated with the progression of autophagy and mitophagy suggested some involvement of these processes in the phenotype of myrAkt An. stephensi. To address this hypothesis, we examined activation levels (phosphorylation) of autophagy-promoting ERK, JNK, and p38 MAPK in the midguts of 3–5 d old, age-matched NTG and HM An. stephensi. Activation levels of all three MAPKs were reduced in the midgut of HM females relative to NTG females (by 40–60%; Fig. 1), which in the context of Akt overexpression, suggested a state of disruption of normal, autophagic repair processes in the midgut epithelium. Together with our LC-MS/MS data, these data suggested that proteins associated with mitochondria and maintenance of the structure of the midgut were altered by tissue-specific Akt overexpression in An. stephensi.

Bottom Line: Despite an apparent increase in mitochondrial biogenesis in young females (3 d), energy deficiencies were apparent as decreased oxidative phosphorylation and increased [AMP]/[ATP] ratios.Hence, Akt-induced changes in mitochondrial dynamics perturb midgut homeostasis to enhance parasite resistance and decrease mosquito infective lifespan.Further, quality control of mitochondrial function in the midgut is necessary for the maintenance of midgut health as reflected in energy homeostasis and tissue repair and renewal.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Microbiology and Immunology, School of Medicine, University of California, Davis, Davis, California, United States of America. sluckhart@ucdavis.edu

ABSTRACT
The overexpression of activated, myristoylated Akt in the midgut of female transgenic Anopheles stephensi results in resistance to infection with the human malaria parasite Plasmodium falciparum but also decreased lifespan. In the present study, the understanding of mitochondria-dependent midgut homeostasis has been expanded to explain this apparent paradox in an insect of major medical importance. Given that Akt signaling is essential for cell growth and survival, we hypothesized that sustained Akt activation in the mosquito midgut would alter the balance of critical pathways that control mitochondrial dynamics to enhance parasite killing at some cost to survivorship. Toxic reactive oxygen and nitrogen species (RNOS) rise to high levels in the midgut after blood feeding, due to a combination of high NO production and a decline in FOXO-dependent antioxidants. Despite an apparent increase in mitochondrial biogenesis in young females (3 d), energy deficiencies were apparent as decreased oxidative phosphorylation and increased [AMP]/[ATP] ratios. In addition, mitochondrial mass was lower and accompanied by the presence of stalled autophagosomes in the posterior midgut, a critical site for blood digestion and stem cell-mediated epithelial maintenance and repair, and by functional degradation of the epithelial barrier. By 18 d, the age at which An. stephensi would transmit P. falciparum to human hosts, mitochondrial dysfunction coupled to Akt-mediated repression of autophagy/mitophagy was more evident and midgut epithelial structure was markedly compromised. Inhibition of RNOS by co-feeding of the nitric-oxide synthase inhibitor L-NAME at infection abrogated Akt-dependent killing of P. falciparum that begins within 18 h of infection in 3-5 d old mosquitoes. Hence, Akt-induced changes in mitochondrial dynamics perturb midgut homeostasis to enhance parasite resistance and decrease mosquito infective lifespan. Further, quality control of mitochondrial function in the midgut is necessary for the maintenance of midgut health as reflected in energy homeostasis and tissue repair and renewal.

Show MeSH
Related in: MedlinePlus