Toll-like Receptor 3-mediated Necrosis via TRIF,RIP3, and MLKL

Toll-like receptor (TLR) signaling is triggered by pathogen-associated molecular patterns that mediate well established cytokine-driven pathways, activating NF-κB together with IRF3/IRF7. In addition, TLR3 drives caspase 8-regulated programmed cell death pathways reminiscent of TNF family death receptor signaling. We find that inhibition or elimination of caspase 8 during stimulation of TLR2, TLR3, TLR4, TLR5, or TLR9 results in receptor interacting protein (RIP) 3 kinase-dependent programmed necrosis that occurs through either TIR domain-containing adapter-inducing interferon-β (TRIF) or MyD88 signal transduction. TLR3 or TLR4 directly activates programmed necrosis through a RIP homotypic interaction motif-dependent association of TRIF with RIP3 kinase (also called RIPK3). In fibroblasts, this pathway proceeds independent of RIP1 or its kinase activity, but it remains dependent on mixed lineage kinase domain-like protein (MLKL) downstream of RIP3 kinase. Here, we describe two small molecule RIP3 kinase inhibitors and employ them to demonstrate the common requirement for RIP3 kinase in programmed necrosis induced by RIP1-RIP3, DAI-RIP3, and TRIF-RIP3 complexes. Cell fate decisions following TLR signaling parallel death receptor signaling and rely on caspase 8 to suppress RIP3-dependent programmed necrosis whether initiated directly by a TRIF-RIP3-MLKL pathway or indirectly via TNF activation and the RIP1-RIP3-MLKL necroptosis pathway.     

Developmental role of the SNF1-related kinase Hunk in pregnancy-induced changes in the mammary gland

The steroid hormones 17 beta-estradiol and progesterone play a central role in the pathogenesis of breast cancer and regulate key phases of mammary gland development. This suggests that developmental regulatory molecules whose activity is influenced by ovarian hormones may also contribute to mammary carcinogenesis. In a screen designed to identify protein kinases expressed in the mammary gland, we previously identified a novel SNF1-related serine/threonine kinase, Hunk (hormonally upregulated Neu-associated kinase). During postnatal mammary development, Hunk mRNA expression is restricted to a subset of mammary epithelial cells and is temporally regulated with highest levels of expression occurring during early pregnancy. In addition, treatment of mice with 17 beta-estradiol and progesterone results in the rapid and synergistic upregulation of Hunk expression in a subset of mammary epithelial cells, suggesting that the expression of this kinase may be regulated by ovarian hormones. Consistent with the tightly regulated pattern of Hunk expression during pregnancy, mammary glands from transgenic mice engineered to misexpress Hunk in the mammary epithelium manifest temporally distinct defects in epithelial proliferation and differentiation during pregnancy, and fail to undergo normal lobuloalveolar development. Together, these observations suggest that Hunk may contribute to changes in the mammary gland that occur during pregnancy in response to ovarian hormones.     

Granulocyte colony-stimulating factor therapy for stem cell mobilization following anterior wall myocardial infarction: the CAPITAL STEM MI randomized trial

Background:

Small studies have yielded divergent results for administration of granulocyte colony-stimulating factor (G-CSF) after acute myocardial infarction. Adequately powered studies involving patients with at least moderate left ventricular dysfunction are lacking.

Methods:

Patients with left ventricular ejection fraction less than 45% after anterior-wall myocardial infarction were treated with G-CSF (10 μg/kg daily for 4 days) or placebo. After initial randomization of 86 patients, 41 in the placebo group and 39 in the G-CSF group completed 6-month follow-up and underwent measurement of left ventricular ejection fraction by radionuclide angiography.

Results:

Baseline and 6-week mean ejection fraction was similar for the G-CSF and placebo groups: 34.8% (95% confidence interval [CI] 32.6%–37.0%) v. 36.4% (95% CI 33.5%–39.2%) at baseline and 39.8% (95% CI 36.2%–43.4%) v. 43.1% (95% CI 39.2%–47.0%) at 6 weeks. However, G-CSF therapy was associated with a lower ejection fraction at 6 months relative to placebo (40.8% [95% CI 37.4%–44.2%] v. 46.0% [95% CI 42.7%–44.3%]). Both groups had improved left ventricular function, but change in left ventricular ejection fraction was lower in patients treated with G-CSF than in those who received placebo (5.7 [95% CI 3.4–8.1] percentage points v. 9.2 [95% CI 6.3–12.1] percentage points). One or more of a composite of several major adverse cardiac events occurred in 8 patients (19%) within each group, with similar rates of target-vessel revascularization.

Interpretation:

In patients with moderate left ventricular dysfunction following anterior-wall infarction, G-CSF therapy was associated with a lower 6-month left ventricular ejection fraction but no increased risk of major adverse cardiac events. Future studies of G-CSF in patients with left ventricular dysfunction should be monitored closely for safety. Trial registration: ClinicalTrials.gov, no. {"type":"clinical-trial","attrs":{"text":"NCT00394498","term_id":"NCT00394498"}}NCT00394498Rapid reperfusion therapy has become the standard treatment for ST-segment elevation myocardial infarction (STEMI), with congestive heart failure and left ventricular dysfunction continuing as the strongest predictors of higher long-term risk.¹ To date, no definitive therapies exist to regenerate myocardium following myocardial necrosis, and myocardial preservation is therefore the goal of STEMI care. Contemporary studies have suggested the possibility of myocardial regeneration by endogenous stem and progenitor cell populations, and preliminary clinical studies have hinted at potential benefit.^2,3 Studies investigating whether postinfarction myocardial function can be improved by enhancing stem cell–mediated repair are in progress ({"type":"clinical-trial","attrs":{"text":"NCT00936819","term_id":"NCT00936819"}}NCT00936819 and {"type":"clinical-trial","attrs":{"text":"NCT00984178","term_id":"NCT00984178"}}NCT00984178).Granulocyte colony-stimulating factor (G-CSF), an endogenously produced glycoprotein growth factor, when given in pharmacologic doses, stimulates mobilization of hematopoietic stem cells into the peripheral blood. Therapeutically, recombinant synthetic forms have been used to enhance recovery from neutropenia following chemotherapy and for mobilization of stem cells before hematopoietic stem cell transplant.⁴ Numerous small clinical studies have investigated the potential of G-CSF–induced mobilization of stem cells in the peri-infarction period to enhance left ventricular recovery, but they have yielded discordant results. However, meta-analyses have suggested benefit for left ventricular ejection fraction in subgroups who received G-CSF early after infarction or in patients whose left ventricular dysfunction was mild to moderate.^5,6 Larger trials are necessary because, in addition to mobilizing stem cells, G-CSF modulates intracellular signalling cascades within cardiomyocytes and can activate neutrophils, and several trials have been stopped early as a result of excessive in-stent restenosis and acute coronary syndromes in patients with coronary artery disease.^7–11 Animal data have similarly yielded discordant results, depending on the dose and timing of G-CSF.¹²To clarify the role of G-CSF in promoting left ventricular recovery after acute myocardial infarction, we performed an adequately powered randomized clinical trial in patients with moderate left ventricular dysfunction following anterior-wall STEMI.     

Costs of defense: correlated responses to divergent selection for foliar glucosinolate content in <Emphasis Type=Italic>Brassica rapa</Emphasis>

The evolutionary response of plant populations to herbivore imposed selection for defense may theoretically be constrained by the costs of defense, yet few studies convincingly demonstrate such costs. We investigated possible constraints on the evolution of defense in rapid cycling Brassica rapa by divergently selecting lines for investment in foliar glucosinolate content, a chemical defense in this species. Costs would then result in a significant correlated response to artificially imposed selection in the direction opposite to the direct response of foliar glucosinolate production. Correlated responses of date of first flowering, total flower number, number of seeds per fruit, and mean seed mass were examined. After three generations of selection, there was a significant direct response in glucosinolate content of the leaves of B. rapa. Furthermore, we found significant correlated responses in both total flower production and number of seeds produced per fruit, but not date of first flowering or mean seed mass. Lines selected for high glucosinolates produced fewer flowers and seeds per fruit compared to those selected for low glucosinolates while lines selected for low glucosinolates showed the opposite response. Thus, costs of defense were demonstrated and may constrain the evolution of foliar glucosinolate production in this plant species.     

Light environment and the impacts of foliage quality on herbivorous insect attack and bird predation

Theory predicts that variation in plant traits will modify both the direct interactions between plants and herbivores and the indirect impacts of predators of those herbivores. Light has strong effects on leaf quality, so the impacts of herbivores and predators may differ between plants grown in sun and shade. However, past experiments have often been unable to separate the effects of light environment on plant traits and herbivory from direct effects on herbivores and predators. We first manipulated light availability in an open habitat using a shade cloth pre-treatment to produce oak saplings with different leaf qualities. Leaves on plants exposed to high light were thicker and tougher and had lower nitrogen and water contents, and higher carbon and phenolic contents than leaves on plants under a shade cloth. Then, in the main experiment, we moved all plants to a common shade environment where bird predators were excluded in a factorial design. We measured insect herbivore abundance and leaf damage. Herbivores were significantly more abundant and caused greater leaf damage on sun trees, although these leaf characteristics are usually associated with low-quality food. Bird exclusion did not change herbivore abundance but did increase leaf damage. Contrary to our predictions, the effects of birds did not differ between trees grown in sun and shade conditions. Thus, differences in effects of predators on herbivores and plants between light habitats, when observed, might be due to variation in predator abundance and not bottom-up effects of host plant quality.