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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 led to morphological changes in the epithelium and mitochondria of the An. stephensi midgut.Posterior midgut morphology of NTG An. stephensi (3 d (A) and 18 d (B) after adult emergence), HT myrAkt An. stephensi (3 d (C) and 18 d (D) after adult emergence), and HM myrAkt An. stephensi (3 d (E) and 18 d (F) after adult emergence). Midguts from 3 d NTG, HT, and HM An. stephensi had an intact brush border (BB) and mitochondria (M) localized near the brush border (A, C, E). Stalled autophagosomes (SA) were observed in the midguts of 3 d HM (E) and 18 d HM and HT mosquitoes (D, F). Giant stalled autophagosomes (GSA) were found in the midguts of 18 d HM and HT mosquitoes (D, F). Many SAs contained electron dense material consistent with engulfed mitochondria (E, F). An example of a clear, double membrane, autophagic vacuole fusing with a small, apparently damaged, mitochondrion in the midgut of 3 d HM (white arrowhead, E inset) indicated mitophagy in process. In addition, the mitochondria in 18 d HM mosquitoes were not localized to the brush border, but distributed through the cytoplasm (F). An inset shows example of a stalled autophagosome containing three partially degraded mitochondria in an 18 d HT midgut (F inset). Representative TEM images taken at a magnification of 2,650× are shown. Inset in (E) is at magnification of 15,000×, and inset in (F) is at 8,800×. Midgut epithelium microvilli or brush border, BB; lysosomes, L; basal lamina mitochondria, M; cell nucleus, N; nucleolus, n; stalled autophagosomes, SA; giant autophagosomes with brush border inside, GSA; secretory granules, SG; white arrows point at representative structures.
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ppat-1003180-g002: Over-expression of myrAKT led to morphological changes in the epithelium and mitochondria of the An. stephensi midgut.Posterior midgut morphology of NTG An. stephensi (3 d (A) and 18 d (B) after adult emergence), HT myrAkt An. stephensi (3 d (C) and 18 d (D) after adult emergence), and HM myrAkt An. stephensi (3 d (E) and 18 d (F) after adult emergence). Midguts from 3 d NTG, HT, and HM An. stephensi had an intact brush border (BB) and mitochondria (M) localized near the brush border (A, C, E). Stalled autophagosomes (SA) were observed in the midguts of 3 d HM (E) and 18 d HM and HT mosquitoes (D, F). Giant stalled autophagosomes (GSA) were found in the midguts of 18 d HM and HT mosquitoes (D, F). Many SAs contained electron dense material consistent with engulfed mitochondria (E, F). An example of a clear, double membrane, autophagic vacuole fusing with a small, apparently damaged, mitochondrion in the midgut of 3 d HM (white arrowhead, E inset) indicated mitophagy in process. In addition, the mitochondria in 18 d HM mosquitoes were not localized to the brush border, but distributed through the cytoplasm (F). An inset shows example of a stalled autophagosome containing three partially degraded mitochondria in an 18 d HT midgut (F inset). Representative TEM images taken at a magnification of 2,650× are shown. Inset in (E) is at magnification of 15,000×, and inset in (F) is at 8,800×. Midgut epithelium microvilli or brush border, BB; lysosomes, L; basal lamina mitochondria, M; cell nucleus, N; nucleolus, n; stalled autophagosomes, SA; giant autophagosomes with brush border inside, GSA; secretory granules, SG; white arrows point at representative structures.

Mentions: The overexpression of myrAkt resulted in significant morphological changes to the An. stephensi posterior midgut (Table 2). Posterior midgut tissue of 3 d and 18 d NTG mosquitoes had a well-defined brush border, intact basal lamina, well-defined nuclei, normal lysosomes, and numerous mitochondria that tended to localize near the brush border (Figs. 2A, B) as observed in other insect species [52]–[54]. The midgut morphology of 3 d HT and HM females were similar to those of NTGs with most structures comparable to NTG mosquitoes. However, a significantly higher prevalence of midguts from 3 d transgenic mosquitoes had cytoplasmic inclusions (40% HT and 60% HM) that were less common or absent in midguts from NTG females (20%; Table 2). Based on morphology (outer double membrane around electron dense material, membrane-like structures, membrane-bound structures with cristae-like organization; [55], [56]), these inclusions were likely stalled autophagosomes of various sizes (Figs. 2E). Mitochondrial autophagy in particular was evident as either mitochondrial membranes engulfed by a developing phagolysosome or as autophagosome-associated mitochondrial degradation (Fig. 2E, Finsets).


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 led to morphological changes in the epithelium and mitochondria of the An. stephensi midgut.Posterior midgut morphology of NTG An. stephensi (3 d (A) and 18 d (B) after adult emergence), HT myrAkt An. stephensi (3 d (C) and 18 d (D) after adult emergence), and HM myrAkt An. stephensi (3 d (E) and 18 d (F) after adult emergence). Midguts from 3 d NTG, HT, and HM An. stephensi had an intact brush border (BB) and mitochondria (M) localized near the brush border (A, C, E). Stalled autophagosomes (SA) were observed in the midguts of 3 d HM (E) and 18 d HM and HT mosquitoes (D, F). Giant stalled autophagosomes (GSA) were found in the midguts of 18 d HM and HT mosquitoes (D, F). Many SAs contained electron dense material consistent with engulfed mitochondria (E, F). An example of a clear, double membrane, autophagic vacuole fusing with a small, apparently damaged, mitochondrion in the midgut of 3 d HM (white arrowhead, E inset) indicated mitophagy in process. In addition, the mitochondria in 18 d HM mosquitoes were not localized to the brush border, but distributed through the cytoplasm (F). An inset shows example of a stalled autophagosome containing three partially degraded mitochondria in an 18 d HT midgut (F inset). Representative TEM images taken at a magnification of 2,650× are shown. Inset in (E) is at magnification of 15,000×, and inset in (F) is at 8,800×. Midgut epithelium microvilli or brush border, BB; lysosomes, L; basal lamina mitochondria, M; cell nucleus, N; nucleolus, n; stalled autophagosomes, SA; giant autophagosomes with brush border inside, GSA; secretory granules, SG; white arrows point at representative structures.
© Copyright Policy
Related In: Results  -  Collection

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

ppat-1003180-g002: Over-expression of myrAKT led to morphological changes in the epithelium and mitochondria of the An. stephensi midgut.Posterior midgut morphology of NTG An. stephensi (3 d (A) and 18 d (B) after adult emergence), HT myrAkt An. stephensi (3 d (C) and 18 d (D) after adult emergence), and HM myrAkt An. stephensi (3 d (E) and 18 d (F) after adult emergence). Midguts from 3 d NTG, HT, and HM An. stephensi had an intact brush border (BB) and mitochondria (M) localized near the brush border (A, C, E). Stalled autophagosomes (SA) were observed in the midguts of 3 d HM (E) and 18 d HM and HT mosquitoes (D, F). Giant stalled autophagosomes (GSA) were found in the midguts of 18 d HM and HT mosquitoes (D, F). Many SAs contained electron dense material consistent with engulfed mitochondria (E, F). An example of a clear, double membrane, autophagic vacuole fusing with a small, apparently damaged, mitochondrion in the midgut of 3 d HM (white arrowhead, E inset) indicated mitophagy in process. In addition, the mitochondria in 18 d HM mosquitoes were not localized to the brush border, but distributed through the cytoplasm (F). An inset shows example of a stalled autophagosome containing three partially degraded mitochondria in an 18 d HT midgut (F inset). Representative TEM images taken at a magnification of 2,650× are shown. Inset in (E) is at magnification of 15,000×, and inset in (F) is at 8,800×. Midgut epithelium microvilli or brush border, BB; lysosomes, L; basal lamina mitochondria, M; cell nucleus, N; nucleolus, n; stalled autophagosomes, SA; giant autophagosomes with brush border inside, GSA; secretory granules, SG; white arrows point at representative structures.
Mentions: The overexpression of myrAkt resulted in significant morphological changes to the An. stephensi posterior midgut (Table 2). Posterior midgut tissue of 3 d and 18 d NTG mosquitoes had a well-defined brush border, intact basal lamina, well-defined nuclei, normal lysosomes, and numerous mitochondria that tended to localize near the brush border (Figs. 2A, B) as observed in other insect species [52]–[54]. The midgut morphology of 3 d HT and HM females were similar to those of NTGs with most structures comparable to NTG mosquitoes. However, a significantly higher prevalence of midguts from 3 d transgenic mosquitoes had cytoplasmic inclusions (40% HT and 60% HM) that were less common or absent in midguts from NTG females (20%; Table 2). Based on morphology (outer double membrane around electron dense material, membrane-like structures, membrane-bound structures with cristae-like organization; [55], [56]), these inclusions were likely stalled autophagosomes of various sizes (Figs. 2E). Mitochondrial autophagy in particular was evident as either mitochondrial membranes engulfed by a developing phagolysosome or as autophagosome-associated mitochondrial degradation (Fig. 2E, Finsets).

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