Low nuclear levels of nuclear factor-kappa B are essential for KC self-induction in astrocytes: requirements for shuttling and phosphorylation

The impact of astrocytic NF-κB on healthy and Alzheimer's disease brains

Astrocytes play a role in healthy cognitive function and Alzheimer's disease (AD). The transcriptional factor nuclear factor-κB (NF-κB) drives astrocyte diversity, but the mechanisms are not fully understood. By combining studies in human brains and animal models and selectively manipulating NF-κB function in astrocytes, we deepened the understanding of the role of astrocytic NF-κB in brain health and AD. In silico analysis of bulk and cell-specific transcriptomic data revealed the association of NF-κB and astrocytes in AD. Confocal studies validated the higher level of p50 NF-κB and phosphorylated-p65 NF-κB in glial fibrillary acidic protein (GFAP)+-astrocytes in AD versus non-AD subjects. In the healthy mouse brain, chronic activation of astrocytic NF-κB disturbed the proteomic milieu, causing a loss of mitochondrial-associated proteins and the rise of inflammatory-related proteins. Sustained NF-κB signaling also led to microglial reactivity, production of pro-inflammatory mediators, and buildup of senescence-related protein p16INK4A in neurons. However, in an AD mouse model, NF-κB inhibition accelerated β-amyloid and tau accumulation. Molecular biology studies revealed that astrocytic NF-κB activation drives the increase in GFAP and inflammatory proteins and aquaporin-4, a glymphatic system protein that assists in mitigating AD. Our investigation uncovered fundamental mechanisms by which NF-κB enables astrocytes' neuroprotective and neurotoxic responses in the brain.

Role of inflammatory chemokines in hypertension

Hypertension is associated with immune cells activation and their migration into the kidney, vasculature, heart and brain. These inflammatory mechanisms are critical for blood pressure regulation and mediate target organ damage, creating unique novel targets for pharmacological modulation. In response to angiotensin II and other pro-hypertensive stimuli, the expression of several inflammatory chemokines and their receptors is increased in the target organs, mediating homing of immune cells. In this review, we summarize the contribution of key inflammatory chemokines and their receptors to increased accumulation of immune cells in target organs and effects on vascular dysfunction, remodeling, oxidative stress and fibrosis, all of which contribute to blood pressure elevation. In particular, the role of CCL2, CCL5, CXCL8, CXCL9, CXCL10, CXCL11, CXCL16, CXCL1, CX3CL1, XCL1 and their receptors in the context of hypertension is discussed. Recent studies have tested the efficacy of pharmacological or genetic targeting of chemokines and their receptors on the development of hypertension. Promising results indicate that some of these pathways may serve as future therapeutic targets to improve blood pressure control and prevent target organ consequences including kidney failure, heart failure, atherosclerosis or cognitive impairment.

Nucleocytoplasmic p27Kip1 Export Is Required for ERK1/2-Mediated Reactive Astroglial Proliferation Following Status Epilepticus

Reactive astrogliosis is a prominent and ubiquitous reaction of astrocytes to many types of brain injury. Up-regulation of glial fibrillary acidic protein (GFAP) expression and astroglial proliferation are hallmarks of reactive astrogliosis. However, the mechanisms that regulate reactive astrogliosis remain elusive. In the present study, status epilepticus (SE, a prolonged seizure activity) led to reactive astrogliosis showing the increases in GFAP expression and the number of proliferating astrocytes with prolonged extracellular signal receptor-activated kinases 1/2 (ERK1/2) activation and reduced nuclear p27^Kip1 level. U0126, an ERK1/2 inhibitor, showed opposite effects. Leptomycin B (LMB), an inhibitor of chromosomal maintenance 1 (CRM1), attenuated nucleocytoplasmic p27^Kip1 export and astroglial proliferation, although it up-regulated ERK1/2 phosphorylation and GFAP expression. Roscovitine ameliorated the reduced nuclear p27^Kip1 level and astroglial proliferation without changing GFAP expression and ERK1/2 phosphorylation. U0126 aggravated SE-induced astroglial apoptosis in the molecular layer of the dentate gyrus that was unaffected by LMB and roscovitine. In addition, U0126 exacerbated SE-induced neuronal death, while LMB mitigated it. Roscovitine did not affect SE-induced neuronal death. The present data elucidate for the first time the roles of nucleocytoplasmic p27^Kip1 transport in ERK1/2-mediated reactive astrogliosis independent of SE-induced neuronal death and astroglial apoptosis. Therefore, our findings suggest that nucleocytoplasmic p27^Kip1 export may be required for ERK1/2-mediated astroglial proliferation during reactive astrogliosis, and that nuclear p27^Kip1 entrapment may be a potential therapeutic strategy for anti-proliferation in reactive astrocytes.

Interactions of Opioids and HIV Infection in the Pathogenesis of Chronic Pain

Over 50% of HIV-1/AIDS patients suffer chronic pain. Currently, opioids are the cornerstone medications for treating severe pain in these patients. Ironically, emerging clinical data indicates that repeated use of opiate pain medicines might in fact heighten the chronic pain states in HIV patients. Both laboratory-based and clinical studies strongly suggest that opioids exacerbate the detrimental effects of HIV-1 infection on the nervous system, both on neurons and glia. The combination of opioids and HIV-1infection may promote the damage of neurons, including those in the pain sensory and transmission pathway, by activating both caspase-dependent and caspase-independent pro-apoptotic pathways. In addition, the opiate-HIV-1 interaction may also cause widespread disturbance of glial function and elicit glial-derived pro-inflammatory responses that dysregulate neuronal function. The deregulation of neuron-glia cross-talk that occurs with the combination of HIV-1 and opioids appears to play an important role in the development of the pathological pain state. In this article, we wish to provide an overview of the potential molecular and cellular mechanisms by which opioids may interact with HIV-1 to cause neurological problems, especially in the context of HIV-associated pathological pain. Elucidating the underlying mechanisms will help researchers and clinicians to understand how chronic use of opioids for analgesia enhances HIV-associated pain. It will also assist in optimizing therapeutic approaches to prevent or minimize this significant side effect of opiate analgesics in pain management for HIV patients.

Craniotomy: true sham for traumatic brain injury, or a sham of a sham?

Abstract Neurological dysfunction after traumatic brain injury (TBI) is caused by both the primary injury and a secondary cascade of biochemical and metabolic events. Since TBI can be caused by a variety of mechanisms, numerous models have been developed to facilitate its study. The most prevalent models are controlled cortical impact and fluid percussion injury. Both typically use "sham" (craniotomy alone) animals as controls. However, the sham operation is objectively damaging, and we hypothesized that the craniotomy itself may cause a unique brain injury distinct from the impact injury. To test this hypothesis, 38 adult female rats were assigned to one of three groups: control (anesthesia only); craniotomy performed by manual trephine; or craniotomy performed by electric dental drill. The rats were then subjected to behavioral testing, imaging analysis, and quantification of cortical concentrations of cytokines. Both craniotomy methods generate visible MRI lesions that persist for 14 days. The initial lesion generated by the drill technique is significantly larger than that generated by the trephine. Behavioral data mirrored lesion volume. For example, drill rats have significantly impaired sensory and motor responses compared to trephine or naïve rats. Finally, of the seven tested cytokines, KC-GRO and IFN-γ showed significant increases in both craniotomy models compared to naïve rats. We conclude that the traditional sham operation as a control confers profound proinflammatory, morphological, and behavioral damage, which confounds interpretation of conventional experimental brain injury models. Any experimental design incorporating "sham" procedures should distinguish among sham, experimentally injured, and healthy/naïve animals, to help reduce confounding factors.

Morphine exacerbates HIV-1 Tat-induced cytokine production in astrocytes through convergent effects on [Ca(2+)](i), NF-kappaB trafficking and transcription

Astroglia are key cellular sites where opiate drug signals converge with the proinflammatory effects of HIV-1 Tat signals to exacerbate HIV encephalitis. Despite this understanding, the molecular sites of convergence driving opiate-accelerated neuropathogenesis have not been deciphered. We therefore explored potential points of interaction between the signaling pathways initiated by HIV-1 Tat and opioids in striatal astrocytes. Profiling studies screening 152 transcription factors indicated that the nuclear factor-kappa B (NF-kappaB) subunit, c-Rel, was a likely candidate for Tat or Tat plus opiate-induced increases in cytokine and chemokine production by astrocytes. Pretreatment with the NF-kappaB inhibitor parthenolide provided evidence that Tat+/-morphine-induced release of MCP-1, IL-6 and TNF-alpha by astrocytes is NF-kappaB dependent. The nuclear export inhibitor, leptomycin B, blocked the nucleocytoplasmic shuttling of NF-kappaB; causing p65 (RelA) accumulation in the nucleus, and significantly attenuated cytokine production in Tat+/-morphine exposed astrocytes. Similarly, chelating intracellular calcium ([Ca(2+)](i)) blocked Tat+/-morphine-evoked MCP-1 and IL-6 release, while artificially increasing the concentration of extracellular Ca(2+) reversed this effect. Taken together, these results demonstrate that: 1) exposure to Tat+/-morphine is sufficient to activate NF-kappaB and cytokine production, 2) the release of MCP-1 and IL-6 by Tat+/-morphine are highly Ca(2+)-dependent, while TNF-alpha appears to be less affected by the changes in [Ca(2+)](i), and 3) in the presence of Tat, exposure to opiates augments Tat-induced NF-kappaB activation and cytokine release through a Ca(2+)-dependent pathway.

Chemokines and Chemokine Receptors Critical to Host Resistance following Genital Herpes Simplex Virus Type 2 (HSV-2) Infection

HSV-2 is a highly successful human pathogen with a remarkable ability to elude immune detection or counter the innate and adaptive immune response through the production of viral-encoded proteins. In response to infection, resident cells secrete soluble factors including chemokines that mobilize and guide leukocytes including T and NK cells, neutrophils, and monocytes to sites of infection. While there is built-in redundancy within the system, chemokines signal through specific membrane-bound receptors that act as antennae detailing a chemical pathway that will provide a means to locate and eliminate the viral insult. Within the central nervous system (CNS), the temporal and spatial expression of chemokines relative to leukocyte mobilization in response to HSV-2 infection has not been elucidated. This paper will review some of the chemokine/chemokine receptor candidates that appear critical to the host in viral resistance and clearance from the CNS and peripheral tissue using murine models of genital HSV-2 infection.

RNAi screen in mouse astrocytes identifies phosphatases that regulate NF-kappaB signaling

Regulation of NF-kappaB activation is controlled by a series of kinases; however, the roles of phosphatases in regulating this pathway are poorly understood. We report a systematic RNAi screen of phosphatases that modulate NF-kappaB activity. Nineteen of 250 phosphatase genes were identified as regulators of NF-kappaB signaling in astrocytes. RNAi selectively regulates endogenous chemokine and cytokine expression. Coimmunoprecipitation identified associations of distinct protein phosphatase 2A core or holoenzymes with the IKK, NF-kappaB, and TRAF2 complexes. Dephosphorylation of these complexes leads to modulation of NF-kappaB transcriptional activity. In contrast to IKK and NF-kappaB, TRAF2 phosphorylation has not been well elucidated. We show that the Thr117 residue in TRAF2 is phosphorylated following TNFalpha stimulation. This phosphorylation process is modulated by PP2A and is required for TRAF2 functional activity. These results provide direct evidence for TNF-induced TRAF2 phosphorylation and demonstrate that phosphorylation is regulated at multiple levels in the NF-kappaB pathway.

NF-kappaB functions in the nervous system: from development to disease

The transcription factor nuclear factor-kappaB (NF-kappaB) is an ubiquitously expressed dimeric molecule with post-translationally regulated activity. Its role in the immune system and host defense has been well characterized over the last two decades. In contrast, our understanding of the function of this transcription factor in the nervous system (NS) is only emerging. Given their cytoplasmic retention and nuclear translocation upon stimulus, NF-kappaB members are likely to exert an important role in transduction of signals from synaptic terminals to nucleus, to initiate transcriptional responses. This report describes recent findings deciphering the diverse functions of NF-kappaB in NS development and activity, which range from the control of cell growth, survival and inflammatory response to synaptic plasticity, behavior and cognition. Particular attention is given to the specific roles of NF-kappaB in the various cells of the NS, e.g. neurons and glia. Current knowledge of the contribution of NF-kappaB to several neurodegenerative disorders, such as Alzheimer's, Parkinson's and Huntington's diseases is also summarized.

Differential regulation of the CXCR2 chemokine network in rat brain trauma: Implications for neuroimmune interactions and neuronal survival

Chemokine receptors represent promising targets to attenuate inflammatory responses and subsequent secondary damage after brain injury. We studied the response of the chemokines CXCL1/CINC-1 and CXCL2/MIP-2 and their receptors CXCR1 and CXCR2 after controlled cortical impact injury in adult rats. Rapid upregulation of CXCL1/CINC-1 and CXCL2/MIP-2, followed by CXCR2 (but not CXCR1), was observed after injury. Constitutive neuronal CXCR2 immunoreactivity was detected in several brain areas, which rapidly but transiently downregulated upon trauma. A second CXCR2-positive compartment, mainly colocalized with the activated microglia/macrophage marker ED1, was detected rapidly after injury in the ipsilateral cortex, progressively emerging into deeper areas of the brain later in time. It is proposed that CXCR2 has a dual role after brain injury: (i) homologous neuronal CXCR2 downregulation would render neurons more vulnerable to injury, whereas (ii) chemotaxis and subsequent differentiation of blood-borne cells into a microglial-like phenotype would be promoted by the same receptor.

Upregulation of chemokine CXCL1/KC by leptospiral membrane lipoprotein preparation in renal tubule epithelial cells

We have previously shown that leptospiral membrane lipoprotein preparation (LMLP) extracted from pathogenic Leptospira santarosai serovar Shermani stimulates the secretion of pro-inflammatory mediators in renal tubule epithelial cells, and implicated its role in the initiation of tubulointerstitial nephritis. Renal tubulointerstitial injury is characterized by inflammatory cell infiltrate; however, the stimuli for leukocyte recruitment are not fully understood. Initial studies by cytokine protein array analysis revealed significant upregulation of neutrophil-chemoattractant keratinocyte-derived chemokine (CXCL1/KC) at nanogram range of LMLP stimulation in cultured murine proximal tubule cells (PTCs). As PTCs express Toll-like receptors (TLRs), this study investigated the roles of TLR signaling pathways in PTCs stimulated by LMLP and its relation to CXCL1/KC secretion. The LMLP stimulated the early secretion of CXCL1/KC and enhanced the level of TLR2 mRNA expression in PTCs through time- and dose-dependent effect. The LMLP-stimulated secretion of human growth-related oncogene alpha, a functional homolog to murine KC, in TLR-defective human embryonic kidney 293 cells transiently transfected with TLR2-expressing plasmids and the response was augmented by coexpression of TLR1 and TLR2. Moreover, silencing of TLR2, myeloid differentiation factor 88, and TNF receptor-associated factor 6 with specific small interfering RNA significantly reduces the response caused by LMLP in PTCs. The LMLP-stimulated CXCL1/KC secretion was also significantly reduced by pre-incubating PTCs with a specific p38 inhibitor. These results indicate that LMLP stimulates the production of CXCL1/KC to recruit polymorphonuclear neutrophils at the site of inflammation through a TLR2-mediated pathway in renal tubule cells.