Significance: The imino acid proline is utilized by different organisms to offset cellular imbalances caused by environmental stress. The wide use in nature of proline as a stress adaptor molecule indicates that proline has a fundamental biological role in stress response. Understanding the mechanisms by which proline enhances abiotic/biotic stress response will facilitate agricultural crop research and improve human health. Recent Advances: It is now recognized that proline metabolism propels cellular signaling processes that promote cellular apoptosis or survival. Studies have shown that proline metabolism influences signaling pathways by increasing reactive oxygen species (ROS) formation in the mitochondria via the electron transport chain. Enhanced ROS production due to proline metabolism has been implicated in the hypersensitive response in plants, lifespan extension in worms, and apoptosis, tumor suppression, and cell survival in animals. Critical Issues: The ability of proline to influence disparate cellular outcomes may be governed by ROS levels generated in the mitochondria. Defining the threshold at which proline metabolic enzyme expression switches from inducing survival pathways to cellular apoptosis would provide molecular insights into cellular redox regulation by proline. Are ROS the only mediators of proline metabolic signaling or are other factors involved? Future Directions: New evidence suggests that proline biosynthesis enzymes interact with redox proteins such as thioredoxin. An important future pursuit will be to identify other interacting partners of proline metabolic enzymes to uncover novel regulatory and signaling networks of cellular stress response. Antioxid. Redox Signal. 19, 998-1011.

Emerging evidence suggests that n-3 polyunsaturated fatty acids (PUFA) promote brown adipose tissue thermogenesis. However, the underlying mechanisms remain elusive. Here, we hypothesize that n-3 PUFA promotes brown adipogenesis by modulating miRNAs. To test this hypothesis, murine brown preadipocytes were induced to differentiate the fatty acids of palmitic, oleate, or eicosapentaenoic acid (EPA). The increases of brown-specific signature genes and oxygen consumption rate by EPA were concurrent with up-regulation of miR-30b and 378 but not by oleate or palmitic acid. Next, we hypothesize that free fatty acid receptor 4 (Ffar4), a functional receptor for n-3 PUFA, modulates miR-30b and 378. Treatment of Ffar4 agonist (GW9508) recapitulated the thermogenic activation of EPA by increasing oxygen consumption rate, brown-specific marker genes, and miR-30b and 378, which were abrogated in Ffar4-silenced cells. Intriguingly, addition of the miR-30b mimic was unable to restore EPA-induced Ucp1 expression in Ffar4-depleted cells, implicating that Ffar4 signaling activity is required for up-regulating the brown adipogenic program. Moreover, blockage of miR-30b or 378 by locked nucleic acid inhibitors significantly attenuated Ffar4 as well as brown-specific signature gene expression, suggesting the signaling interplay between Ffar4 and miR-30b/378. The association between miR-30b/378 and brown thermogenesis was also confirmed in fish oil-fed C57/BL6 mice. Interestingly, the Ffar4 agonism-mediated signaling axis of Ffar4-miR-30b/378-Ucp1 was linked with an elevation of cAMP in brown adipocytes, similar to cold-exposed or fish oil-fed brown fat. Taken together, our work identifies a novel function of Ffar4 in modulating brown adipogenesis partly through a mechanism involving cAMP activation and upregulation of miR-30b and miR-378.There are two specific types of fat with opposite functions, brown adipose tissue (BAT) 3 and white adipose tissue (WAT).WAT stores energy in the form of triglyceride, whereas BAT dissipates energy in the form of heat via uncoupling protein 1 (UCP1) (1). Recent advances in our understanding of BAT biology in humans have provided a new insight into weight loss strategies by boosting BAT thermogenesis. Despite the surge of research for identifying cellular and molecular regulators of brown fat development (2, 3), the role of dietary constituents, particularly dietary fatty acids (FA), in thermogenic activation is poorly understood. Depending on the degree of desaturation and the n-6/n-3 ratio, FA differentially control adiposity, insulin sensitivity, immune response (4), and probably energy expenditure (5-7). Lately, it has been suggested that n-3 polyunsaturated FA (PUFA) stimulate beige/brown adipogenesis in primary murine adipogenic precursor cells (5) as well as C57BL/6 mice (6, 7). The latter animal study suggests that n-3 PUFA are associated with sympathetic activation and increased ␤3-adrenergic receptor (Adrb3) signaling (7). However, the underlying mechanistic details of how dietary n-3 PUFA...

Zika virus (ZIKV), a mosquito-transmitted flavivirus responsible for sporadic outbreaks of mild and febrile illness in Africa and Asia, reemerged in the last decade causing serious human diseases, including microcephaly, congenital malformations, and Guillain-Barré syndrome. Although genomic and phylogenetic analyses suggest that genetic evolution may have led to the enhanced virulence of ZIKV, experimental evidence supporting the role of specific genetic changes in virulence is currently lacking. One sequence motif, VNDT, containing an N-linked glycosylation site in the envelope (E) protein, is polymorphic; it is absent in many of the African isolates but present in all isolates from the recent outbreaks. In the present study, we investigated the roles of this sequence motif and glycosylation of the E protein in the pathogenicity of ZIKV. We first constructed a stable full-length cDNA clone of ZIKV in a novel linear vector from which infectious virus was recovered. The recombinant ZIKV generated from the infectious clone, which contains the VNDT motif, is highly pathogenic and causes lethality in a mouse model. In contrast, recombinant viruses from which the VNDT motif is deleted or in which the N-linked glycosylation site is mutated by single-amino-acid substitution are highly attenuated and nonlethal. The mutant viruses replicate poorly in the brains of infected mice when inoculated subcutaneously but replicate well following intracranial inoculation. Our findings provide the first evidence that N-linked glycosylation of the E protein is an important determinant of ZIKV virulence and neuroinvasion.IMPORTANCE The recent emergence of Zika virus (ZIKV) in the Americas has caused major worldwide public health concern. The virus appears to have gained significant pathogenicity, causing serious human diseases, including microcephaly and Guillain-Barré syndrome. The factors responsible for the emergence of pathogenic ZIKV are not understood at this time, although genetic changes have been shown to facilitate virus transmission. All isolates from the recent outbreaks contain an N-linked glycosylation site within the viral envelope (E) protein, whereas many isolates of the African lineage virus lack this site. To elucidate the functional significance of glycosylation in ZIKV pathogenicity, recombinant ZIKVs from infectious clones with or without the glycan on the E protein were generated. ZIKVs lacking the glycan were highly attenuated for the ability to cause mortality in a mouse model and were severely compromised for neuroinvasion. Our studies suggest glycosylation of the E protein is an important factor contributing to ZIKV pathogenicity.

Proline metabolism has an underlying role in apoptotic signaling that impacts tumorigenesis. Proline is oxidized to glutamate in the mitochondria with the rate limiting step catalyzed by proline dehydrogenase (PRODH). PRODH expression is inducible by p53 leading to increased proline oxidation, reactive oxygen species (ROS) formation, and induction of apoptosis. Paradoxical to its role in apoptosis, proline also protects cells against oxidative stress. Here we explore the mechanism of proline protection against hydrogen peroxide stress in melanoma WM35 cells. Treatment of WM35 cells with proline significantly increased cell viability, diminished oxidative damage of cellular lipids and proteins, and retained ATP and NADPH levels after exposure to hydrogen peroxide. Inhibition or siRNA-mediated knockdown of PRODH abolished proline protection against oxidative stress whereas knockdown of Δ1-pyrroline-5-carboxylate reductase, a key enzyme in proline biosynthesis, had no impact on proline protection. Potential linkages between proline metabolism and signaling pathways were explored. The combined inhibition of the mammalian target of rapamycin complex 1 (mTORC1) and mTORC2 eliminated proline protection. A significant increase in Akt activation was observed in proline treated cells after hydrogen peroxide stress along with a corresponding increase in the phosphorylation of the fork head transcription factor class O3a (FoxO3a). The role of PRODH in proline mediated protection was validated in the prostate carcinoma cell line, PC3. Knockdown of PRODH in PC3 cells attenuated phosphorylated levels of Akt and FoxO3a and decreased cell survival during hydrogen peroxide stress. The results provide evidence that PRODH is essential in proline protection against hydrogen peroxide mediated cell death and that proline/PRODH helps activate Akt in cancer cells.

These results suggest that evidence of oxygen free radicals is also found early in the development of fibrosis and cirrhosis in both models.