Authors: Madenspacher JH, Azzam KM, Gowdy KM, Malcolm KC, Nick JA, Dixon D, Aloor JJ, Draper DW, Guardiola JJ, Shatz M, Menendez D, Lowe J, Lu J, Bushel P, Li L, Merrick BA, Resnick MA, Fessler MB
Journal: J Exp Med. 2013 May 6;210(5):891-904. doi: 10.1084/jem.20121674. Epub 2013 Apr 29
Cancer and infection are predominant causes of human mortality and derive, respectively, from inadequate genomic and host defenses against environmental agents. The transcription factor p53 plays a central role in human tumor suppression. Despite its expression in immune cells and broad responsiveness to stressors, it is virtually unknown whether p53 regulates host defense against infection. We report that the lungs of naive p53(-/-) mice display genome-wide induction of NF-κB response element-enriched proinflammatory genes, suggestive of type 1 immune priming. p53-null and p53 inhibitor-treated mice clear Gram-negative and -positive bacteria more effectively than controls after intrapulmonary infection. This is caused, at least in part, by cytokines produced by an expanded population of apoptosis-resistant, TLR-hyperresponsive alveolar macrophages that enhance airway neutrophilia. p53(-/-) neutrophils, in turn, display heightened phagocytosis, Nox-dependent oxidant generation, degranulation, and bacterial killing. p53 inhibition boosts bacterial killing by mouse neutrophils and oxidant generation by human neutrophils. Despite enhanced bacterial clearance, infected p53(-/-) mice suffer increased mortality associated with aggravated lung injury. p53 thus modulates host defense through regulating microbicidal function and fate of phagocytes, revealing a fundamental link between defense of genome and host during environmental insult.
Authors: Lujan SA, Williams JS, Clausen AR, Clark AB, Kunkel TA
Journal: Mol Cell. 2013 May 9;50(3):437-43. doi: 10.1016/j.molcel.2013.03.017. Epub 2013 Apr 18
To maintain genome stability, mismatch repair of nuclear DNA replication errors must be directed to the nascent strand, likely by DNA ends and PCNA. Here we show that the efficiency of mismatch repair in Saccharomyces cerevisiae is reduced by inactivating RNase H2, which nicks DNA containing ribonucleotides incorporated during replication. In strains encoding mutator polymerases, this reduction is preferential for repair of mismatches made by leading-strand DNA polymerase ε as compared to lagging-strand DNA polymerase δ. The results suggest that RNase-H2-dependent processing of ribonucleotides transiently present in DNA after replication may direct mismatch repair to the continuously replicated nascent leading strand.
Authors: Allende ML, Sipe LM, Tuymetova G, Wilson-Henjum KL, Chen W, Proia RL
Journal: J Biol Chem. 2013 May 1. [Epub ahead of print]
Sphingosine-1-phosphate (S1P) is a bioactive lipid whose levels are tightly regulated by its synthesis and degradation. Intracellularly, S1P is dephosphorylated by the actions of two S1P-specific phosphatases, sphingosine-1-phosphate phosphatase 1 and 2. To identify the physiologic functions of S1P phosphatase 1, we have studied mice with its gene, Sgpp1, deleted. Sgpp1-/- mice appeared normal at birth, but during the first week of life exhibited stunted growth and suffered desquamation, with most dying before weaning. Both Sgpp1-/- pups and surviving adults exhibited multiple epidermal abnormalities. Interestingly, the epidermal permeability barrier developed normally during embryogenesis in Sgpp1-/- mice. Keratinocytes isolated from the skin of Sgpp1-/- pups had increased intracellular S1P levels, and displayed a gene expression profile that indicated overexpression of genes associated with keratinocyte differentiation. The results reveal S1P metabolism as a regulator of keratinocyte differentiation and epidermal homeostasis.
Authors: Mishra SK, Hoon MA
Journal: Science. 2013 May 24;340(6135):968-71. doi: 10.1126/science.1233765
Itch is triggered by somatosensory neurons expressing the ion channel TRPV1 (transient receptor potential cation channel subfamily V member 1), but the mechanisms underlying this nociceptive response remain poorly understood. Here, we show that the neuropeptide natriuretic polypeptide b (Nppb) is expressed in a subset of TRPV1 neurons and found that Nppb(-/-) mice selectively lose almost all behavioral responses to itch-inducing agents. Nppb triggered potent scratching when injected intrathecally in wild-type and Nppb(-/-) mice, showing that this neuropeptide evokes itch when released from somatosensory neurons. Itch responses were blocked by toxin-mediated ablation of Nppb-receptor-expressing cells, but a second neuropeptide, gastrin-releasing peptide, still induced strong responses in the toxin-treated animals. Thus, our results define the primary pruriceptive neurons, characterize Nppb as an itch-selective neuropeptide, and reveal the next two stages of this dedicated neuronal pathway.
Authors: Molina-Cruz A, Garver LS, Alabaster A, Bangiolo L, Haile A, Winikor J, Ortega C, van Schaijk BC, Sauerwein RW, Taylor-Salmon E, Barillas-Mury C
Journal: Science. 2013 May 24;340(6135):984-7. doi: 10.1126/science.1235264
Plasmodium falciparum transmission by Anopheles gambiae mosquitoes is remarkably efficient, resulting in a very high prevalence of human malaria infection in sub-Saharan Africa. A combination of genetic mapping, linkage group selection, and functional genomics was used to identify Pfs47 as a P. falciparum gene that allows the parasite to infect A. gambiae without activating the mosquito immune system. Disruption of Pfs47 greatly reduced parasite survival in the mosquito, and this phenotype could be reverted by genetic complementation of the parasite or by disruption of the mosquito complement-like system. Pfs47 suppresses midgut nitration responses that are critical to activate the complement-like system. We provide direct experimental evidence that immune evasion mediated by Pfs47 is critical for efficient human malaria transmission by A. gambiae.
Authors: Mukherjee P, Woods TA, Moore RA, Peterson KE
Journal: Immunity. 2013 Apr 18;38(4):705-16. doi: 10.1016/j.immuni.2013.02.013
La Crosse virus (LACV), a zoonotic Bunyavirus, is a major cause of pediatric viral encephalitis in the United States. A hallmark of neurological diseases caused by LACV and other encephalitic viruses is the induction of neuronal cell death. Innate immune responses have been implicated in neuronal damage, but no mechanism has been elucidated. By using in vitro studies in primary neurons and in vivo studies in mice, we have shown that LACV infection induced the RNA helicase, RIG-I, and mitochondrial antiviral signaling protein (MAVS) signaling pathway, resulting in upregulation of the sterile alpha and TIR-containing motif 1 (SARM1), an adaptor molecule that we found to be directly involved in neuronal damage. SARM1-mediated cell death was associated with induced oxidative stress response and mitochondrial damage. These studies provide an innate-immune signaling mechanism for virus-induced neuronal death and reveal potential targets for development of therapeutics to treat encephalitic viral infections.
Authors: Li H, Edin ML, Bradbury JA, Graves JP, Degraff LM, Gruzdev A, Cheng J, Dackor RT, Wang PM, Bortner CD, Garantziotis S, Jetten AM, Zeldin DC
Journal: Am J Respir Crit Care Med. 2013 Apr 15;187(8):812-22. doi: 10.1164/rccm.201211-2073OC
Rationale: Helper CD4(+) T cell subsets, including IL-9- and IL-10-producing T helper cell type 9 (Th9) cells, exist under certain inflammatory conditions. Cyclooxygenase (COX)-1 and COX-2 play important roles in allergic lung inflammation and asthma. It is unknown whether COX-derived eicosanoids regulate Th9 cells during allergic lung inflammation. Objectives: To determine the role of COX metabolites in regulating Th9 cell differentiation and function during allergic lung inflammation. Methods: COX-1(-/-), COX-2(-/-), and wild-type (WT) mice were studied in an in vivo model of ovalbumin-induced allergic inflammation and an in vitro model of Th9 differentiation using flow cytometry, cytokine assays, confocal microscopy, real-time PCR, and immunoblotting. In addition, the role of specific eicosanoids and their receptors was examined using synthetic prostaglandins (PGs), selective inhibitors, and siRNA knockdown. Measurements and Main Results: Experimental endpoints were not different between COX-1(-/-) and WT mice; however, the percentage of IL-9(+) CD4(+) T cells was increased in lung, bronchoalveolar lavage fluid, lymph nodes, and blood of allergic COX-2(-/-) mice relative to WT. Bronchoalveolar lavage fluid IL-9 and IL-10, serum IL-9, and lung IL-17RB levels were significantly increased in allergic COX-2(-/-) mice or in WT mice treated with COX-2 inhibitors. IL-9, IL-10, and IL-17RB expression in vivo was inhibited by PGD2 and PGE2, which also reduced Th9 cell differentiation of murine and human naive CD4(+) T cells in vitro. Inhibition of protein kinase A significantly increased Th9 cell differentiation of naive CD4(+) T cells isolated from WT mice in vitro. Conclusions: COX-2-derived PGD2 and PGE2 regulate Th9 cell differentiation by suppressing IL-17RB expression via a protein kinase A-dependent mechanism.
Authors: Weil EJ, Fufaa G, Jones LI, Lovato T, Lemley KV, Hanson RL, Knowler WC, Bennett PH, Yee B, Myers BD, Nelson RG
Journal: Diabetes. 2013 Apr 1. [Epub ahead of print]
Angiotensin receptor blockers are renoprotective in hypertensive azotemic patients with type 2 diabetes, but their efficacy in early diabetic kidney disease is uncertain. We performed a 6-year randomized clinical trial in 169 American Indians with type 2 diabetes and normoalbuminuria (albumin/creatinine ratio [ACR] <30 mg/g; n = 91) or microalbuminuria (ACR 30-299 mg/g; n = 78) at baseline. The primary outcome was decline in glomerular filtration rate (GFR) to ≤60 mL/min or to half the baseline value in subjects who entered with GFR <120 mL/min. Another outcome was differences in glomerular structure at end of treatment. Subjects received 100 mg losartan or placebo daily. GFR was measured annually; 111 subjects underwent kidney biopsies. Only nine subjects reached the GFR outcome, and the unadjusted hazard ratio (losartan vs. placebo) was 0.50 (95% CI 0.12-1.99). Differences in mesangial fractional volume were not estimated in the combined albuminuria groups because of an interaction with treatment assignment. In separate analyses, mesangial fractional volume was lower in subjects treated with losartan in the microalbuminuria group (18.8 vs. 25.6%; P = 0.02), but not in the normoalbuminuria group (19.6 vs. 17.8%; P = 0.86). Treatment with losartan may preserve some features of kidney structure in American Indians with type 2 diabetes and microalbuminuria.
Authors: Ebrahim S, Fujita T, Millis BA, Kozin E, Ma X, Kawamoto S, Baird MA, Davidson M, Yonemura S, Hisa Y, Conti MA, Adelstein RS, Sakaguchi H, Kachar B
Journal: Curr Biol. 2013 Apr 22;23(8):731-6. doi: 10.1016/j.cub.2013.03.039
Fluorescent probes attached to proteins in the epithelial belt show the precisely structured network connecting individual epithelial cells.
Nonmuscle myosin II (NMII) is thought to be the master integrator of force within epithelial apical junctions, mediating epithelial tissue morphogenesis and tensional homeostasis. Mutations in NMII are associated with a number of diseases due to failures in cell-cell adhesion. However, the organization and the precise mechanism by which NMII generates and responds to tension along the intercellular junctional line are still not known. We discovered that periodic assemblies of bipolar NMII filaments interlace with perijunctional actin and α-actinin to form a continuous belt of muscle-like sarcomeric units (∼400-600 nm) around each epithelial cell. Remarkably, the sarcomeres of adjacent cells are precisely paired across the junctional line, forming an integrated, transcellular contractile network. The contraction/relaxation of paired sarcomeres concomitantly impacts changes in apical cell shape and tissue geometry. We show differential distribution of NMII isoforms across heterotypic junctions and evidence for compensation between isoforms. Our results provide a model for how NMII force generation is effected along the junctional perimeter of each cell and communicated across neighboring cells in the epithelial organization. The sarcomeric network also provides a well-defined target to investigate the multiple roles of NMII in junctional homeostasis as well as in development and disease.
Authors: Jain S, de Azua IR, Lu H, White MF, Guettier JM, Wess J
Journal: J Clin Invest. 2013 Mar 8. pii: 66432. doi: 10.1172/JCI66432. [Epub ahead of print]
Type 2 diabetes (T2D) has emerged as a major threat to human health in most parts of the world. Therapeutic strategies aimed at improving pancreatic β cell function are predicted to prove beneficial for the treatment of T2D. In the present study, we demonstrate that drug-mediated, chronic, and selective activation of β cell Gq signaling greatly improve β cell function and glucose homeostasis in mice. These beneficial metabolic effects were accompanied by the enhanced expression of many genes critical for β cell function, maintenance, and differentiation. By employing a combination of in vivo and in vitro approaches, we identified a novel β cell pathway through which receptor-activated Gq leads to the sequential activation of ERK1/2 and IRS2 signaling, thus triggering a series of events that greatly improve β cell function. Importantly, we found that chronic stimulation of a designer Gq-coupled receptor selectively expressed in β cells prevented both streptozotocin-induced diabetes and the metabolic deficits associated with the consumption of a high-fat diet in mice. Since β cells are endowed with numerous receptors that mediate their cellular effects via activation of Gq-type G proteins, our findings provide a rational basis for the development of novel antidiabetic drugs targeting this class of receptors.