Summary During pathogenesis, Mycobacterium tuberculosis (Mtb) colonizes environments, such as the macrophage or necrotic granuloma, that are acidic and rich in cholesterol and fatty acids. The goal of this study was to examine how acidic pH and available carbon sources interact to regulate Mtb physiology. Here we report that Mtb growth at acidic pH requires host-associated carbon sources that function at the intersection of glycolysis and the TCA cycle, such as pyruvate, acetate, oxaloacetate and cholesterol. In contrast, in other tested carbon sources, Mtb fully arrests its growth at acidic pH and establishes a state of non-replicating persistence. Growth-arrested Mtb is resuscitated by the addition of pyruvate suggesting that growth arrest is due to a pH-dependent checkpoint on metabolism. Additionally, we demonstrate that the phoPR two-component regulatory system is required to slow Mtb growth at acidic pH and functions to maintain redox homeostasis. Transcriptional profiling and functional metabolic studies demonstrate that signals from acidic pH and carbon source are integrated to remodel pathways associated with anaplerotic central metabolism, lipid anabolism and the regeneration of oxidized cofactors. Because phoPR is required for Mtb virulence in animals, we suggest that pH-driven adaptation may be critical to Mtb pathogenesis.

The Mycobacterium tuberculosis (Mtb) DosRST two-component regulatory system promotes the survival of Mtb during non-replicating persistence (NRP). NRP bacteria help drive the long course of tuberculosis therapy; therefore, chemical inhibition of DosRST may inhibit the ability of Mtb to establish persistence and thus shorten treatment. Using a DosRST-dependent fluorescent Mtb reporter strain, a whole-cell phenotypic high-throughput screen of a ∼540,000 compound small-molecule library was conducted. The screen discovered novel inhibitors of the DosRST regulon, including three compounds that were subject to follow-up studies: artemisinin, HC102A and HC103A. Under hypoxia, all three compounds inhibit Mtb-persistence-associated physiological processes, including triacylglycerol synthesis, survival and antibiotic tolerance. Artemisinin functions by disabling the heme-based DosS and DosT sensor kinases by oxidizing ferrous heme and generating heme-artemisinin adducts. In contrast, HC103A inhibits DosS and DosT autophosphorylation activity without targeting the sensor kinase heme.

Background-In patients with left ventricular infarction or dilatation, leaflet tethering by displaced papillary muscles frequently induces mitral regurgitation, which doubles mortality. Little is known about the biological potential of the mitral valve (MV) to compensate for ventricular remodeling. We tested the hypothesis that MV leaflet surface area increases over time with mechanical stretch created by papillary muscle displacement through cell activation, not passive stretching. Methods and Results-Under cardiopulmonary bypass, the papillary muscle tips in 6 adult sheep were retracted apically short of producing mitral regurgitation to replicate tethering without confounding myocardial infarction or turbulence. Diastolic leaflet area was quantified by 3-dimensional echocardiography over 61Ϯ6 days compared with 6 unstretched sheep MVs. Total diastolic leaflet area increased by 2.4Ϯ1.3 cm 2 (17Ϯ10%) from 14.3Ϯ1.9 to 16.7Ϯ1.9 cm 2 (Pϭ0.006) with stretch with no change in the unstretched valves despite sham open heart surgery. Stretched MVs were 2.8 times thicker than normal (1.18Ϯ0.14 versus 0.42Ϯ0.14 mm; PϽ0.0001) at 60 days with an increased spongiosa layer. Endothelial cells (CD31 ϩ ) coexpressing ␣-smooth muscle actin were significantly more common by fluorescent cell sorting in tethered versus normal leaflets (41Ϯ19% versus 9Ϯ5%; Pϭ0.02), indicating endothelial-mesenchymal transdifferentiation. ␣-Smooth muscle actin-positive cells appeared in the atrial endothelium, penetrating into the interstitium, with increased collagen deposition. Thickened chordae showed endothelial and subendothelial ␣-smooth muscle actin. Endothelial-mesenchymal transdifferentiation capacity also was demonstrated in cultured MV endothelial cells. Conclusions-Mechanical stresses imposed by papillary muscle tethering increase MV leaflet area and thickness, with cellular changes suggesting reactivated embryonic developmental pathways. Understanding such actively adaptive mechanisms can potentially provide therapeutic opportunities to augment MV area and reduce ischemic mitral regurgitation. (Circulation. 2009;120:334-342.)Key Words: echocardiography Ⅲ mitral valve Ⅲ valves I n population studies, valvular heart disease is common, with mitral regurgitation (MR) most prevalent. 1 Although degeneration is the leading cause of MR surgical repair, 2 coronary artery disease with myocardial infarction and left ventricular (LV) dysfunction frequently causes functional MR as a result of global LV remodeling and sphericity 3-5 or localized inferoposterior wall remodeling 6 -12 ; both cause apical, posterior, and outward displacement of the papillary muscles (PMs) 6 -12 and mitral valve (MV) leaflet tethering 13 that prevents effective closure ( Figure 1A and 1B). 12,14 Editorial see p 275 Clinical Perspective on p 342Patients who develop MR after myocardial infarction or with congestive heart failure, even after surgical or catheter revascularization, have doubled mortality and in- To observe leaflet adaptation to tethering over time, we asse...

BackgroundThe mitochondrial unfolded protein response (mitoUPR) is a stress response pathway activated by disruption of proteostasis in the mitochondria. This pathway has been proposed to influence lifespan, with studies suggesting that mitoUPR activation has complex effects on longevity.ResultsHere, we examined the contribution of the mitoUPR to the survival and lifespan of three long-lived mitochondrial mutants in Caenorhabditis elegans by modulating the levels of ATFS-1, the central transcription factor that mediates the mitoUPR. We found that clk-1, isp-1, and nuo-6 worms all exhibit an ATFS-1-dependent activation of the mitoUPR. While loss of atfs-1 during adulthood does not affect lifespan in any of these strains, absence of atfs-1 during development prevents clk-1 and isp-1 worms from reaching adulthood and reduces the lifespan of nuo-6 mutants. Examining the mechanism by which deletion of atfs-1 reverts nuo-6 lifespan to wild-type, we find that many of the transcriptional changes present in nuo-6 worms are mediated by ATFS-1. Genes exhibiting an ATFS-1-dependent upregulation in nuo-6 worms are enriched for transcripts that function in stress response and metabolism. Consistent, with this finding, loss of atfs-1 abolishes the enhanced stress resistance observed in nuo-6 mutants and prevents upregulation of multiple stress response pathways including the HIF-1-mediated hypoxia response, SKN-1-mediated oxidative stress response and DAF-16-mediated stress response.ConclusionsOur results suggest that in the long-lived mitochondrial mutant nuo-6 activation of the mitoUPR causes atfs-1-dependent changes in the expression of genes involved in stress response and metabolism, which contributes to the extended longevity observed in this mutant. This work demonstrates that the mitoUPR can modulate multiple stress response pathways and suggests that it is crucial for the development and lifespan of long-lived mitochondrial mutants.Electronic supplementary materialThe online version of this article (10.1186/s12915-018-0615-3) contains supplementary material, which is available to authorized users.