Viral and Latent Reservoir Persistence in HIV-1–Infected Patients on Therapy

Despite many years of potent antiretroviral therapy, latently infected cells and low levels of plasma virus have been found to persist in HIV-infected patients. The factors influencing this persistence and their relative contributions have not been fully elucidated and remain controversial. Here, we address these issues by developing and employing a simple, but mechanistic viral dynamics model. The model has two novel features. First, it assumes that latently infected T cells can undergo bystander proliferation without transitioning into active viral production. Second, it assumes that the rate of latent cell activation decreases with time on antiretroviral therapy due to the activation and subsequent loss of latently infected cells specific for common antigens, leaving behind cells that are successively less frequently activated. Using the model, we examined the quantitative contributions of T cell bystander proliferation, latent cell activation, and ongoing viral replication to the stability of the latent reservoir and persisting low-level viremia. Not surprisingly, proliferation of latently infected cells helped maintain the latent reservoir in spite of loss of latent infected cells through activation and death, and affected viral dynamics to an extent that depended on the magnitude of latent cell activation. In the limit of zero latent cell activation, the latent cell pool and viral load became uncoupled. However, as the activation rate increased, the plasma viral load could be maintained without depleting the latent reservoir, even in the absence of viral replication. The influence of ongoing viral replication on the latent reservoir remained insignificant for drug efficacies above the “critical efficacy” irrespective of the activation rate. However, for lower drug efficacies viral replication enabled the stable maintenance of both the latent reservoir and the virus. Our model and analysis methods provide a quantitative and qualitative framework for probing how different viral and host factors contribute to the dynamics of the latent reservoir and the virus, offering new insights into the principal determinants of their persistence

Essential role of protein tyrosine phosphatase 1B in obesity-induced inflammation and peripheral insulin resistance during aging

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of insulin signaling and a therapeutic target for type 2 diabetes (T2DM). In this study, we have evaluated the role of PTP1B in the development of aging-associated obesity, inflammation, and peripheral insulin resistance by assessing metabolic parameters at 3 and 16 months in PTP1B) ⁄ ) mice maintained on mixed genetic background (C57Bl ⁄ 6J · 129Sv ⁄ J). Whereas fat mass and adipocyte size were increased in wild-type control mice at 16 months, these parameters did not change with aging in PTP1B) ⁄ ) mice. Increased levels of pro-inflammatory cytokines, crown-like structures, and hypoxia-inducible factor (HIF)-1a wereobserved only in adipose tissue from 16-month-old wild-type mice. Similarly, islet hyperplasia and hyperinsulinemia were observed in wild-type mice with agingassociated obesity, but not in PTP1B) ⁄ ) animals. Leanness in 16- month-old PTP1B) ⁄ ) mice was associated with increased energy expenditure. Whole-body insulin sensitivity decreased in 16- month-old control mice; however, studies with the hyperinsulinemic– euglycemic clamp revealed that PTP1B deficiency prevented this obesity-related decreased peripheral insulin sensitivity. At a molecular level, PTP1B expression and enzymatic activity were upregulated in liver and muscle of 16-month-old wild-type mice as were the activation of stress kinases and the expression of p53. Conversely, insulin receptor-mediated Akt ⁄ Foxo1 signaling was attenuated in these aged control mice. Collectively, these data implicate PTP1B in the development of inflammation and insulin resistance associated with obesity during aging and suggest that inhibition of this phosphatase by therapeutic strategies might protect against age-dependentT2DMThis work was supported by grants from Ministerio de Ciencia e Innovación (Spain) SAF2009-08114 and (to A.M.V.), BFU2008- 04901-C03-02 and 03 (to M.R and J.M.C., respectively), BFU2008-01283 (to M.V), Comunidad de Madrid S2010/BMD- 2423 and Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM) (Instituto Salud Carlos III). CBMSO is recipient of institutional aid from Ramón Areces Foundation. We also acknowledge grants NIH-R01 DK080756, ADA 7-07-RA-80, and NIH U24-DK093000 (to J.K.K.) and UMass Mouse Phenotyping Center supported by UMass Diabetes and Endocrinology Research Center Grant (DK32520) and EFSD/Amylin Programme 2011 grant (to A.M.V.)

The transcription cofactor CRTC1 protects from aberrant hepatic lipid accumulation

Nonalcoholic fatty liver disease (NAFLD) is a rapidly emerging global health-problem. NAFLD encompasses a range of conditions associated with hepatic steatosis, aberrant accumulation of fat in hepatocytes. Although obesity and metabolic syndrome are considered to have a strong association with NAFLD, genetic factors that predispose liver to NAFLD and molecular mechanisms by which excess hepatic lipid develops remain largely unknown. We report that the transcription cofactor CRTC1 confers broad spectrum protection against hepatic steatosis development. CRTC1 directly interferes with the expression of genes regulated by lipogenic transcription factors, most prominently liver x receptor α (LXRα). Accordingly, Crtc1 deficient mice develop spontaneous hepatic steatosis in young age. As a cyclic AMP effector, CRTC1 mediates anti-steatotic effects of calorie restriction (CR). Notably, CRTC1 also mediates anti-lipogenic effects of bile acid signaling, whereas it is negatively regulated by miR-34a, a pathogenic microRNA upregulated in a broad spectrum of NAFLD. These patterns of gene function and regulation of CRTC1 are distinct from other CR-responsive proteins, highlighting critical protective roles that CRTC1 selectively plays against NAFLD development, which in turn provides novel opportunities for selectively targeting beneficial therapeutic effects of CR

The transcription factor MafB promotes anti-inflammatory M2 polarization and cholesterol efflux in macrophages

Macrophages play pivotal roles in the progression and regression of atherosclerosis. Accumulating evidence suggests that macrophage polarization into an anti-inflammatory M2 state is a key characteristic of atherosclerotic plaques undergoing regression. However, the molecular mechanisms underlying this potential association of the M2 polarization with atherosclerosis regression remain poorly understood. Further, human genetic factors that facilitate these anti-atherogenic processes remain largely unknown. We report that the transcription factor MafB plays pivotal roles in promoting macrophage M2 polarization. Further, MafB promotes cholesterol efflux from macrophage foam cells by directly up-regulating its key cellular mediators. Notably, MafB expression is significantly up-regulated in response to various metabolic and immunological stimuli that promote macrophage M2 polarization or cholesterol efflux, and thereby MafB mediates their beneficial effects, in both liver x receptor (LXR)-dependent and independent manners. In contrast, MafB is strongly down-regulated upon elevated pro-inflammatory signaling or by pro-inflammatory and pro-atherogenic microRNAs, miR-155 and miR-33. Using an integrative systems biology approach, we also revealed that M2 polarization and cholesterol efflux do not necessarily represent inter-dependent events, but MafB is broadly involved in both the processes. These findings highlight physiological protective roles that MafB may play against atherosclerosis progression

Effect of Ongoing Viral Replication (ɛ < 1) on the Latent Reservoir, Plasma Viral Load, and the Contribution of Ongoing Viral Replication to the Level of the Latent Reservoir Measured by the Ratio of the Rate of Production of Latently Infected Cells by Ongoing Viral Replication to the Net Removal Rate of Latently Infected Cells

<div><p>The results were obtained for ɛ values above (ɛ = 0.7 > ɛ<i>_c</i>), at (ɛ = 0.1402 = ɛ<i>_c</i>), and slightly below (ɛ = 0.133 < ɛ<i>_c</i>) the critical drug efficacy (ɛ<i>_c</i>) when <i>a_min</i> = 0, <i>r</i> = −0.00171 d⁻¹, and ω = 0.00939 d⁻¹.</p><p>(A) Latent reservoir.</p><p>(B) Plasma viral load.</p><p>(C) Contribution of ongoing viral replication.</p></div

Effect of Persistent Low-Level Activation of the Latent Reservoir on the Latent Reservoir and on Plasma Viral Load

<div><p>When there is no ongoing viral replication (ɛ = 1) and the rate of bystander proliferation of the latent reservoir is equal to the minimum activation rate (<i>r</i> = <i>a_min</i>), i.e., at the bifurcation condition.</p><p>(A) Latent reservoir.</p><p>(B) Plasma viral load.</p></div

Simulated Decay Dynamics of HIV-1 after the Initiation of ART

<div><p>The initial conditions and parameters used in the simulation are given in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.0020135#s4" target="_blank">Materials and Methods</a>. The results are shown for three different drug efficacies (ɛ = 0.3, 0.5, and 0.7).</p><p>(A) Viral decay profile.</p><p>(B) Contribution of long-lived infected cells to plasma virus (φ₁(<i>t</i>) = <i>p_MM*</i>(<i>t</i>) / (<i>N</i>δ<i>T*</i>(<i>t</i>) + <i>p_MM*</i>(<i>t</i>))).</p></div

Effect of the Bystander Proliferation of the Latent Reservoir on the Latent Reservoir and on Plasma Viral Load

<div><p>When there is no ongoing viral replication (ɛ = 1) and the minimum activation rate of the latent reservoir is zero (<i>a</i>_min = 0). The open circles indicate the decay kinetics of the latent reservoir suggested by Strain et al. [<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.0020135#pcbi-0020135-b030" target="_blank">30</a>], where they found t_1/2 ≈ 18 wk up to week 35 and t_1/2 ≈ 58 wk for the subsequent 3 y. The solid curve with <i>r</i> = −0.00171 d⁻¹ and ω = 0.00939 d⁻¹ represents the best-fit curve to the data.</p><p>(A) Latent reservoir.</p><p>(B) Plasma viral load.</p></div

Robust Growth of Human Immunodeficiency Virus Type 1 (HIV-1)

The persistence of human immunodeficiency virus type-1 (HIV-1) has long been attributed to its high mutation rate and the capacity of its resulting heterogeneous virus populations to evade host immune responses and antiviral drugs. However, this view is incomplete because it does not explain how the virus persists in light of the adverse effects mutations in the viral genome and variations in host functions can potentially have on viral functions and growth. Here we show that the resilience of HIV-1 can be credited, at least in part, to a robust response to perturbations that emerges as an intrinsic property of its intracellular development. Specifically, robustness in HIV-1 arises through the coupling of two feedback loops: a Rev-mediated negative feedback and a Tat-mediated positive feedback. By employing a mechanistic kinetic model for its growth we found that HIV-1 buffers the effects of many potentially detrimental variations in essential viral and cellular functions, including the binding of Rev to mRNA; the level of rev mRNA in the pool of fully spliced mRNA; the splicing of mRNA; the Rev-mediated nuclear export of incompletely-spliced mRNAs; and the nuclear import of Tat and Rev. The virus did not, however, perform robustly to perturbations in all functions. Notably, HIV-1 tended to amplify rather than buffer adverse effects of variations in the interaction of Tat with viral mRNA. This result shows how targeting therapeutics against molecular components of the viral positive-feedback loop open new possibilities and potential in the effective treatment of HIV-1