mTORC1-S6K activation by endotoxin contributes to cytokine up-regulation and early lethality in animals

Ribosomal proteins: the missing piece in the inflammation puzzle?

Ribosomal proteins (RPs) are constituents of macromolecular machinery, ribosome that translates genetic information into proteins. Besides ribosomal functions, RPs are now getting appreciated for their 'moonlighting'/extra-ribosomal functions modulating many cellular processes. Accumulating evidence suggests that a number of RPs are involved in inflammation. Though acute inflammation is a part of the innate immune response, uncontrolled inflammation is a driving factor for several chronic inflammatory diseases. An in-depth understanding of inflammation regulation has always been valued for the better management of associated diseases. Hence, this review first outlines the common livelihood of RPs and then provides a comprehensive account of five RPs that significantly contribute to the inflammation process. Finally, we discuss the possible therapeutic uses of RPs against chronic inflammatory diseases.

Divergent regulation of inflammatory cytokines by mTORC1 in THP-1-derived macrophages and intestinal epithelial Caco-2 cells

AIMS

The sustained activation of intestinal mechanistic target of rapamycin complex 1 (mTORC1) brought about by repeated mucosal insult or injury has been linked to escalation of gut inflammatory response, which may progress to damage the epithelium if not controlled. This study investigated the role of mTORC1 in the response of macrophage and enterocyte to inflammatory stimuli.

MATERIALS AND METHODS

We genetically manipulated human THP-1 monocytes and epithelial intestinal Caco-2 cells to generate stable cell lines with baseline, low or high mTORC1 kinase activity. The effects of THP-1 macrophage secretions onto Caco-2 cells were investigated by means of conditioned media transfer experiments.

KEY FINDINGS

The priming of mTORC1 for activation promoted lipopolysaccharide (LPS)-mediated THP-1 macrophage immune response as evidenced by the stimulation of inflammatory mediators (TNFα, IL-6, IL-8, IL-1β and IL-10). The treatment of THP-1 macrophages with LPS more than the manipulated level of mTORC1 activity of macrophages determined whether cytokine gene expression was induced in Caco-2 cells. LPS carry over was not responsible for the stimulation of Caco-2 cells' cytokine response. Knocking down Raptor in Caco-2 cells or treating Caco-2 cells with rapamycin enhanced Caco-2 TNFα gene expression revealing the anti-inflammatory role of a functional mTORC1 in intestinal epithelial cells exposed to macrophage-derived pro-inflammatory stimuli.

SIGNIFICANCE

Taken together, mTORC1 differentially impacts the immune responses of THP-1-derived macrophages and Caco-2 epithelial cells when placed in a pro-inflammatory microenvironment.

mTOR inhibition as a possible pharmacological target in the management of systemic inflammatory response and associated neuroinflammation by lipopolysaccharide challenge in rats

Neuroinflammation plays a critical role during sepsis triggered by microglial activation. Mammalian target of rapamycin (mTOR) has gained attraction in neuroinflammation, however, the mechanism remains unclear. Our goal was to assess the effects of mTOR inhibition by rapamycin on inflammation, microglial activation, oxidative stress, and apoptosis associated with the changes in the inhibitor-κB (IκB)-α/nuclear factor-κB (NF-κB)/hypoxia-inducible factor-1α (HIF-1α) pathway activity following a systemic challenge with lipopolysaccharide (LPS). Rats received saline (10 mL/kg), LPS (10 mg/kg), and (or) rapamycin (1 mg/kg) intraperitoneally. Inhibition of mTOR by rapamycin blocked phosphorylated form of ribosomal protein S6, NF-κB p65 activity by increasing degradation of IκB-α in parallel with HIF-1α expression increased by LPS in the kidney, heart, lung, and brain tissues. Rapamycin attenuated the increment in the expression of tumor necrosis factor-α and interleukin-1β, the inducible nitric oxide synthase, gp91^phox, and p47^phox in addition to nitrite levels elicited by LPS in tissues or sera. Concomitantly, rapamycin treatment reduced microglial activation, brain expression of caspase-3, and Bcl-2-associated X protein while it increased expression of B cell lymphoma 2 induced by LPS. Overall, this study supports the hypothesis that mTOR contributes to the detrimental effect of LPS-induced systemic inflammatory response associated with neuroinflammation via IκB-α/NF-κB/HIF-1α signaling pathway.

Glycolytic reprogramming of macrophages activated by NOD1 and TLR4 agonists: No association with proinflammatory cytokine production in normoxia

Upon activation with pathogen-associated molecular patterns, metabolism of macrophages and dendritic cells is shifted from oxidative phosphorylation to aerobic glycolysis, which is considered important for proinflammatory cytokine production. Fragments of bacterial peptidoglycan (muramyl peptides) activate innate immune cells through nucleotide-binding oligomerization domain (NOD) 1 and/or NOD2 receptors. Here, we show that NOD1 and NOD2 agonists induce early glycolytic reprogramming of human monocyte-derived macrophages (MDM), which is similar to that induced by the Toll-like receptor 4 (TLR4) agonist lipopolysaccharide. This glycolytic reprogramming depends on Akt kinases, independent of mTOR complex 1 and is efficiently inhibited by 2-deoxy-d-glucose (2-DG) or by glucose starvation. 2-DG inhibits proinflammatory cytokine production by MDM and monocyte-derived dendritic cells activated by NOD1 or TLR4 agonists, except for tumor necrosis factor production by MDM, which is inhibited initially, but augmented 4 h after addition of agonists and later. However, 2-DG exerts these effects by inducing unfolded protein response rather than by inhibiting glycolysis. By contrast, glucose starvation does not cause unfolded protein response and, in normoxic conditions, only marginally affects proinflammatory cytokine production triggered through NOD1 or TLR4. In hypoxia mimicked by treating MDM with oligomycin (a mitochondrial ATP synthase inhibitor), both 2-DG and glucose starvation strongly suppress tumor necrosis factor and interleukin-6 production and compromise cell viability. In summary, the requirement of glycolytic reprogramming for proinflammatory cytokine production in normoxia is not obvious, and effects of 2-DG on cytokine responses should be interpreted cautiously. In hypoxia, however, glycolysis becomes critical for cytokine production and cell survival.

Pharmacological preconditioning with the cellular stress inducer thapsigargin protects against experimental sepsis

Previous studies have shown that pretreatment with thapsigargin (TG), a cellular stress inducer, produced potent protective actions against various pathologic injuries. So far there is no information on the effects of TG on the development of bacterial sepsis. Using lipopolysaccharides- and cecal ligation/puncture-induced sepsis models in mice, we demonstrated that preconditioning with a single bolus administration of TG conferred significant improvements in survival. The beneficial effects of TG were not mediated by ER stress induction or changes in Toll-like receptor 4 signaling. In vivo and in cultured macrophages, we identified that TG reduced the protein production of pro-inflammatory cytokines, but exhibited no significant effects on steady state levels of their transcriptions. Direct measurement on the fraction of polysome-bound mRNAs revealed that TG reduced the translational efficiency of pro-inflammatory cytokines in macrophages. Moreover, we provided evidence suggesting that repression of the mTOR (the mammalian target of rapamycin) signaling pathway, but not activation of the PERK (protein kinase R-like endoplasmic reticulum kinase)-eIF2α (eukaryotic initiation factor 2α) pathway, might be involved in mediating the TG effects on cytokine production. In summary, our results support that pharmacological preconditioning with TG may represent a novel strategy to prevent sepsis-induced mortality and organ injuries.

mTORC1 Prevents Epithelial Damage During Inflammation and Inhibits Colitis-Associated Colorectal Cancer Development

Epithelial cells lining the intestinal mucosa constitute a selective-semipermeable barrier acting as first line of defense in the organism. The number of those cells remains constant during physiological conditions, but disruption of epithelial cell homeostasis has been observed in several pathologies. During colitis, epithelial cell proliferation decreases and cell death augments. The mechanism responsible for these changes remains unknown. Here, we show that the pro-inflammatory cytokine IFNγ contributes to the inhibition of epithelial cell proliferation in intestinal epithelial cells (IECs) by inducing the activation of mTORC1. Activation of mTORC1 in response to IFNγ was detected in IECs present along the crypt axis and in colonic macrophages. mTORC1 inhibition enhances cell proliferation, increases DNA damage in IEC. In macrophages, mTORC1 inhibition strongly reduces the expression of pro-inflammatory markers. As a consequence, mTORC1 inhibition exacerbated disease activity, increased mucosal damage, enhanced ulceration, augmented cell infiltration, decreased survival and stimulated tumor formation in a model of colorectal cancer CRC associated to colitis. Thus, our findings suggest that mTORC1 signaling downstream of IFNγ prevents epithelial DNA damage and cancer development during colitis.

Deterioration of Organ Function As a Hallmark in Sepsis: The Cellular Perspective

Development of organ dysfunction discriminates sepsis from uncomplicated infection. The paradigm shift implicated by the new sepsis-3 definition holds that initial impairment of any organ can pave the way for multiple organ dysfunction and death. Moreover, the role of the systemic inflammatory response, central element in previous sepsis definitions, has been questioned. Most strikingly, a so far largely underestimated defense mechanism of the host, i.e., "disease tolerance," which aims at maintaining host vitality without reducing pathogen load, has gained increasing attention. Here, we summarize evidence that a dysregulation of critical cellular signaling events, also in non-immune cells, might provide a conceptual framework for sepsis-induced dysfunction of parenchymal organs in the absence of significant cell death. We suggest that key signaling mediators, such as phosphoinositide 3-kinase, mechanistic target of rapamycin, and AMP-activated protein kinase, control the balance of damage and repair processes and thus determine the fate of affected organs and ultimately the host. Therapeutic targeting of these multifunctional signaling mediators requires cell-, tissue-, or organ-specific approaches. These novel strategies might allow stopping the domino-like damage to further organ systems and offer alternatives beyond the currently available strictly supportive therapeutic options.

The IKK-related kinase TBK1 activates mTORC1 directly in response to growth factors and innate immune agonists

The innate immune kinase TBK1 initiates inflammatory responses to combat infectious pathogens by driving production of type I interferons. TBK1 also controls metabolic processes and promotes oncogene-induced cell proliferation and survival. Here, we demonstrate that TBK1 activates mTOR complex 1 (mTORC1) directly. In cultured cells, TBK1 associates with and activates mTORC1 through site-specific mTOR phosphorylation (on S2159) in response to certain growth factor receptors (i.e., EGF-receptor but not insulin receptor) and pathogen recognition receptors (PRRs) (i.e., TLR3; TLR4), revealing a stimulus-selective role for TBK1 in mTORC1 regulation. By studying cultured macrophages and those isolated from genome edited mTOR S2159A knock-in mice, we show that mTOR S2159 phosphorylation promotes mTORC1 signaling, IRF3 nuclear translocation, and IFN-β production. These data demonstrate a direct mechanistic link between TBK1 and mTORC1 function as well as physiologic significance of the TBK1-mTORC1 axis in control of innate immune function. These data unveil TBK1 as a direct mTORC1 activator and suggest unanticipated roles for mTORC1 downstream of TBK1 in control of innate immunity, tumorigenesis, and disorders linked to chronic inflammation.

Endothelial deletion of mTORC1 protects against hindlimb ischemia in diabetic mice via activation of autophagy, attenuation of oxidative stress and alleviation of inflammation

Peripheral arterial disease (PAD) complicated with diabetes mellitus (DM) still remains a thorny issue due to lack of effective strategies. Our previous study has demonstrated that inhibition of mTORC1 protected adipose-derived stromal cells from hindlimb ischemic injury in PAD mice. However, whether inhibition of mTORC1 could protect against PAD in diabetes mellitus and the underlying mechanisms remained elusive. In this study, we employed endothelial-specific raptor (an essential component of the mTORC1 signaling complex) knockout (KO) mice (Tie2-mTORC1^ko) to investigate whether and how mTORC1 downregulation could alleviate hindlimb ischemic injury in diabetic mice. Tie2-mTORC1^ko mice and their wild-type littermates were intraperitoneally injected with streptozocin to induce type 1 diabetic model, after which the hyperglycemic mice were randomly allocated to sham operation or PAD operation (femoral artery ligation). The restoration of hindlimb blood perfusion and recovery of limb functions were improved in diabetic Tie2-mTORC1^ko PAD mice with significant improvements of autophagy, angiogenesis and vascular integrity as well as attenuation of apoptosis, inflammation and oxidative stress. In vitro, high glucose combining with hypoxia/serum deprivation treatment (HG+H/SD) significantly triggered apoptosis, reactive oxygen species generation and inflammation while inhibited autophagy and tube formation in HUVECs. The effect could be accentuated and attenuated by mTORC1 over-expression (TSC2 siRNA) and mTORC1 silencing (raptor siRNA), respectively. Moreover, autophagy inhibitor 3-MA could simulate the effects of TSC2 siRNA while autophagy inducer rapamycin could mimic the effects of raptor siRNA, suggesting that the beneficial effects of mTORC1 deletion were associated with autophagy induction. In conclusion, our present study demonstrates that endothelial mTORC1 deletion protects against hindlimb ischemic injury in diabetic mice possibly via activation of autophagy, attenuation of oxidative stress and alleviation of inflammation. Therapeutics targeting mTORC1 may therefore represents a promising strategy to rescue limb ischemia in diabetes mellitus.

Activation of mTOR/IκB-α/NF-κB pathway contributes to LPS-induced hypotension and inflammation in rats

Mammalian target of rapamycin (mTOR), a serine/threonine kinase plays an important role in various pathophysiological processes including cancer, metabolic diseases, and inflammation. Although mTOR participates in Toll-like receptor 4 signalling in different cell types, the role of this enzyme in sepsis pathogenesis and its effects on hypotension and inflammation in endotoxemic rats remains unclear. In this study we investigated the effects of mTOR inhibition on lipopolysaccharide (LPS)-induced changes on expressions and/or activities of ribosomal protein S6 (rpS6), an mTOR substrate, nuclear factor-κB (NF-κB) p65, inhibitor κB (IκB)-α, inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2 with production of nitric oxide, peroxynitrite, prostacyclin, and tumor necrosis factor (TNF)-α and activity of myeloperoxidase (MPO), which results in hypotension and inflammation. Injection of LPS (10mg/kg, i.p.) to male Wistar rats decreased blood pressure and increased heart rate that were associated with elevated nitrotyrosine, 6-keto-PGF_1α, and TNF-α levels and MPO activity, and increased expressions and/or activities of rpS6, NF-κB p65, iNOS, and COX-2 and decreased expression of IκB-α in renal, cardiac, and vascular tissues. LPS also increased serum and tissue nitrite levels. Rapamycin (1mg/kg, i.p.) given one h after injection of LPS reversed these effects of LPS. These data suggest that the activation of mTOR/IκB-α/NF-κB pathway associated with vasodilator and proinflammatory mediator formation contributes to LPS-induced hypotension and inflammation.

The Fate of the Tumor in the Hands of Microenvironment: Role of TAMs and mTOR Pathway

Since 2000, written with elegance and accuracy, Hanahan and Weinberg have proposed six major hallmarks of cancer and, together, they provide great advances to the understanding of tumoral biology. Our knowledge about tumor behavior has improved and the investigators have now recognized that inflammatory microenvironment may be a new feature for the tumor entities. Macrophages are considered as an important component of tumoral microenvironment. Biologically, two forms of activated macrophages can be observed: classically activated macrophages (M1) and alternative activated macrophages (M2). Despite the canonical pathways that control this puzzle of macrophages polarization, recently, mTOR signaling pathway has been implicated as an important piece in determining the metabolic and functional differentiation of M1 and M2 profiles. Currently, it is believed that macrophages related to tumoral microenvironment present an “M2-like” feature promoting an immunosuppressive microenvironment enhancing tumoral angiogenesis, growth, and metastasis. In the present review we discuss the role of macrophages in the tumor microenvironment and the role of mTOR pathway in M1 and M2 differentiation. We also discuss the recent findings in M1 and M2 polarization as a possible target in the cancer therapy.

Functional kinomics establishes a critical node of volume-sensitive cation-Cl- cotransporter regulation in the mammalian brain

Cell volume homeostasis requires the dynamically regulated transport of ions across the plasmalemma. While the ensemble of ion transport proteins involved in cell volume regulation is well established, the molecular coordinators of their activities remain poorly characterized. We utilized a functional kinomics approach including a kinome-wide siRNA-phosphoproteomic screen, a high-content kinase inhibitor screen, and a kinase trapping-Orbitrap mass spectroscopy screen to systematically identify essential kinase regulators of KCC3 Thr991/Thr1048 phosphorylation - a key signaling event in cell swelling-induced regulatory volume decrease (RVD). In the mammalian brain, we found the Cl--sensitive WNK3-SPAK kinase complex, required for cell shrinkage-induced regulatory volume decrease (RVI) via the stimulatory phosphorylation of NKCC1 (Thr203/Thr207/Thr212), is also essential for the inhibitory phosphorylation of KCC3 (Thr991/Thr1048). This is mediated in vivo by an interaction between the CCT domain in SPAK and RFXV/I domains in WNK3 and NKCC1/KCC3. Accordingly, genetic or pharmacologic WNK3-SPAK inhibition prevents cell swelling in response to osmotic stress and ameliorates post-ischemic brain swelling through a simultaneous inhibition of NKCC1-mediated Cl- uptake and stimulation of KCC3-mediated Cl- extrusion. We conclude that WNK3-SPAK is an integral component of the long-sought "Cl-/volume-sensitive kinase" of the cation-Cl- cotransporters, and functions as a molecular rheostat of cell volume in the mammalian brain.

mTORC1 mediates peptidoglycan induced inflammatory cytokines expression and NF-κB activation in macrophages

Peptidoglycan (PGN) is the major structural component of the bacterial cell wall, especially gram positive bacteria, which induces inflammatory responses. Mammalian target of rapamycin (mTOR) regulates the production of inflammatory cytokines induced by antigens, while the function of mTORC1 in peptidoglycan induced inflammatory response is unknown. This study aims to examine the role and the regulatory mechanism of mTOR signaling pathway in peptidoglycan induced cytokine expression in mouse macrophages. We observed that peptidoglycan upregulated the secretion of proinflammatory cytokines IL-6, TNF-α and anti-inflammatory cytokine IL-10 in a dose- and time-dependent manner. mTORC1 positively regulates IL-6 and TNF-α, but negatively regulates IL-10 secretion. mTORC1 regulates NF-κB p65 activation by degrading IκB-α in response to peptidoglycan. mTOR, NF-κB and STAT3 signaling pathways are involved in peptidoglycan induced inflammatory cytokines expression via a TLR1/TLR2-dependent mechanism in macrophages. Thus, mTORC1 pathway regulates the innate immune response to bacterial peptidoglycan.

Control of macrophage metabolism and activation by mTOR and Akt signaling

Macrophages are pleiotropic cells that assume a variety of functions depending on their tissue of residence and tissue state. They maintain homeostasis as well as coordinate responses to stresses such as infection and metabolic challenge. The ability of macrophages to acquire diverse, context-dependent activities requires their activation (or polarization) to distinct functional states. While macrophage activation is well understood at the level of signal transduction and transcriptional regulation, the metabolic underpinnings are poorly understood. Importantly, emerging studies indicate that metabolic shifts play a pivotal role in control of macrophage activation and acquisition of context-dependent effector activities. The signals that drive macrophage activation impinge on metabolic pathways, allowing for coordinate control of macrophage activation and metabolism. Here we discuss how mTOR and Akt, major metabolic regulators and targets of such activation signals, control macrophage metabolism and activation. Dysregulated macrophage activities contribute to many diseases, including infectious, inflammatory, and metabolic diseases and cancer, thus a better understanding of metabolic control of macrophage activation could pave the way to the development of new therapeutic strategies.

Do airborne biogenic chemicals interact with the PI3K/Akt/mTOR cell signalling pathway to benefit human health and wellbeing in rural and coastal environments?

Living and taking recreation in rural and coastal environments promote health and wellbeing, although the causal factors involved are unclear. It has been proposed that such environments provide a counter to the stresses of everyday living, leading to enhanced mental and physical health. Living in natural environments will result in airborne exposure to a wide range of biogenic chemicals through inhalation and ingestion of airborne microbiota and particles. The "biogenics" hypothesis formulated here is that regular exposure to low concentrations of mixtures of natural compounds and toxins in natural environments confers pleiotropic health benefits by inhibiting the activities of interconnected cell signalling systems, particularly PI3K/Akt/mTORC1. When overactive, Akt and mTOR (mTORC1) can lead to many pathological processes including cancers, diabetes, inflammation, immunosuppression, and neurodegenerative diseases. There is a substantial body of evidence that many natural products (i.e., from bacteria, algae, fungi and higher plants) inhibit the activities of these protein kinases. Other mTOR-related interconnected metabolic control "switches" (e.g., PTEN & NF-κB), autophagy and other cytoprotective processes are also affected by natural products. The "biogenics" hypothesis formulated here is that regular intermittent exposure to a mixture of airborne biogenic compounds in natural environments confers pleiotropic health benefits by inhibiting activities of the highly interconnected PI3K/Akt/mTORC1 system. It is proposed that future experimental exposures to biogenic aerosols in animal models coupled with epidemiology, should target the activities of the various kinases in the PI3K/Akt/mTORC1 systems and related physiological processes for selected urban, rural and coastal populations in order to test this hypothesis.

mTORC1 Regulates Flagellin-Induced Inflammatory Response in Macrophages

Bacterial flagellin triggers inflammatory responses. Phosphoinositide 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) regulate the production of pro- and anti-inflammatory cytokines that are induced by extrinsic antigens, but the function of mTORC1 in flagellin-induced inflammatory response is unknown. The purpose of this study was to examine the role and the mechanism of PI3K/Akt/mTOR pathway in flagellin-induced cytokine expression in mouse macrophages. We observed that flagellin upregulated TNF-α time- and dose-dependently. Flagellin stimulated rapid (<15 min) PI3K/Akt/mTOR phosphorylation that was mediated by TLR5. Inhibition of PI3K with LY294002 and wortmannin, and of mTORC1 with rapamycin decreased flagellin-induced TNF-α and IL-6 expression and cell proliferation. The activation of NF-κB p65 and STAT3 was regulated by mTORC1 via degradation of IκBα and phosphorylation of STAT3 in response to flagellin, respectively. Thus, the PI3K/Akt/mTORC1 pathway regulates the innate immune response to bacterial flagellin. Rapamycin is potential therapy that can regulate host defense against pathogenic infections.

Early molecular and behavioral response to lipopolysaccharide in the WAG/Rij rat model of absence epilepsy and depressive-like behavior, involves interplay between AMPK, AKT/mTOR pathways and neuroinflammatory cytokine release

The mammalian target of rapamycin (mTOR) pathway has been recently indicated as a suitable drug target for the prevention of epileptogenesis. The mTOR pathway is known for its involvement in the control of the immune system. Since neuroinflammation is recognized as a major contributor to epileptogenesis, we wished to examine whether the neuroprotective effects of mTOR modulation could involve a suppression of the neuroinflammatory process in epileptic brain. We have investigated the early molecular mechanisms involved in the effects of intracerebral administration of the lipopolysaccharide (LPS) in the WAG/Rij rat model of absence epilepsy, in relation to seizure generation and depressive-like behavior; we also tested whether the effects of LPS could be modulated by treatment with rapamycin (RAP), a specific mTOR inhibitor. We determined, in specific rat brain areas, levels of p-mTOR/p-p70S6K and also p-AKT/p-AMPK as downstream or upstream indicators of mTOR activity and tested the effects of LPS and RAP co-administration. Changes in the brain levels of pro-inflammatory cytokines IL-1β and TNF-α and their relative mRNA expression levels were measured, and the involvement of nuclear factor-κB (NF-κB) was also examined in vitro. We confirmed that RAP inhibits the aggravation of absence seizures and depressive-like/sickness behavior induced by LPS in the WAG/Rij rats through the activation of mTOR and show that this effect is correlated with the ability of RAP to dampen and delay LPS increases in neuroinflammatory cytokines IL-1β and TNF-α, most likely through inhibition of the activation of NF-κB. Our results suggest that such a mechanism could contribute to the antiseizure, antiepileptogenic and behavioral effects of RAP and further highlight the potential therapeutic usefulness of mTOR inhibition in the management of human epilepsy and other neurological disorders. Furthermore, we show that LPS-dependent neuroinflammatory effects are also mediated by a complex interplay between AKT, AMPK and mTOR with specificity to selective brain areas. In conclusion, neuroinflammation appears to be a highly coordinated phenomenon, where timing of intervention may be carefully evaluated in order to identify the best suitable target.

mTORC1 and mTORC2 play different roles in the functional survival of transplanted adipose-derived stromal cells in hind limb ischemic mice via regulating inflammation in vivo

Poor cell survival severely limits the beneficial effects of stem cell therapy for peripheral arterial disease (PAD). This study was designed to investigate the role of mammalian target of rapamycin (mTOR) in the survival and therapeutic function of transplanted murine adipose-derived stromal cells (mADSCs) in a murine PAD model. mADSCs (1.0 × 10(7)) were isolated from dual-reporter firefly luciferase and enhanced green fluorescent protein-positive transgenic mice, intramuscularly implanted into the hind limb of C57BL/6 mice after femoral artery ligation/excision, and monitored using noninvasive bioluminescence imaging (BLI). Although engrafted mADSCs produced antiapoptotic/proangiogenic effects in vivo by modulating the inflammatory and angiogenic cytokine response involving the mTOR pathway, longitudinal BLI revealed progressive death of post-transplant mADSCs within ~4 weeks in the ischemic hind limb. Selectively targeting mTOR complex-1 (mTORC1) using low-dose rapamycin treatment with mADSCs attenuated proinflammatory cytokines (interleukin [IL]-1β and tumor necrosis factor-alpha [TNF-α]) expression and neutrophil/macrophage infiltration, which overtly promoted mADSCs viability and antiapoptotic/proangiogenic efficacy in vivo. However, targeting dual mTORC1/mTORC2 using PP242 or high-dose rapamycin caused IL-1β/TNF-α upregulation and anti-inflammatory IL-10, IL-6, and vascular endothelial growth factor/vascular endothelial growth factor receptor 2 downregulation, undermining the survival and antiapoptotic/proangiogenic action of mADSCs in vivo. Furthermore, low-dose rapamycin abrogated TNF-α secretion by mADSCs and rescued the cells from hypoxia/reoxygenation-induced death in vitro, while PP242 or high-dose rapamycin exerted proinflammatory effects and promoted cell death. In conclusion, mTORC1 and mTORC2 may differentially regulate inflammation and affect transplanted mADSCs' functional survival in ischemic hind limb. These findings uncover that mTOR may evolve into a promising candidate for mechanism-driven approaches to facilitate the translation of cell-based PAD therapy.

Saquinavir-NO inhibits S6 kinase activity, impairs secretion of the encephalytogenic cytokines interleukin-17 and interferon-gamma and ameliorates experimental autoimmune encephalomyelitis

NO-hybridization of the HIV protease inhibitor Saquinavir generates a new chemical entity named Saq-NO, that retains the anti-viral activity and exerts lower toxicity. We show that Saq-NO inhibited the generation of various cytokines in ConA-stimulated unfractionated murine spleen cells and rat lymph nodes stimulated with ConA as well as in purified CD4(+) T cells in vitro and reduced the circulating levels of cytokines in mice challenged with anti-CD3 antibody. Furthermore, Saq-NO reduced IL-17 and IFN-γ production in myelin basic protein (MBP)-specific cells isolated from rats immunized with MBP. These findings translated well into the in vivo setting as Saq-NO ameliorated the course of the disease in two preclinical models of multiple sclerosis. Our results demonstrate that Saq-NO exerts immunomodulatory effects that warrant studies on its application in autoimmune diseases.

Folate-conjugated rapamycin slows progression of polycystic kidney disease

Activation of the mammalian target of rapamycin (mTOR) signaling pathway is aberrant in autosomal-dominant polycystic kidney disease (ADPKD). The mTOR inhibitors, such as rapamycin, ameliorate PKD in rodent models, but clinical trials have not shown benefit, possibly as a result of low tissue concentrations of rapamycin at clinically tolerable doses. To overcome this limitation, we synthesized a folate-conjugated form of rapamycin (FC-rapa) that is taken up by folate receptor-mediated endocytosis and cleaved intracellularly to reconstitute the active drug. We found that renal cyst-lining cells highly express the folate receptor in ADPKD and mouse models. In vitro, FC-rapa inhibited mTOR activity in a dose- and folate receptor-dependent manner. Treatment of a PKD mouse model with FC-rapa inhibited mTOR in the target tissue, strongly attenuated proliferation and growth of renal cysts and preserved renal function. Furthermore, FC-rapa inhibited mTOR activity in the kidney but not in other organs. In summary, these results suggest that targeting the kidney using FC-rapa may overcome the significant side effects and lack of renal efficacy observed in clinical trials with mTOR inhibitors in ADPKD.