Homocysteine-induced sustained GluN2A NMDA receptor stimulation leads to mitochondrial ROS generation and neurotoxicity

Homocysteine, a sulfur-containing amino acid derived from methionine metabolism, is a known agonist of N-methyl-D-aspartate receptor (NMDAR) and is involved in neurotoxicity. Our previous findings showed that neuronal exposure to elevated homocysteine levels leads to sustained low-level increase in intracellular Ca2+, which is dependent on GluN2A subunit-containing NMDAR (GluN2A-NMDAR) stimulation. These studies further showed a role of ERK MAPK in homocysteine-GluN2A-NMDAR-mediated neuronal death. However, the intracellular mechanisms associated with such sustained GluN2A-NMDAR stimulation and subsequent Ca2+ influx have remained unexplored. Using live-cell imaging with Fluo3-AM and biochemical approaches, we show that homocysteine-GluN2A NMDAR-induced initial Ca2+ influx triggers sequential phosphorylation and subsequent activation of the proline rich tyrosine kinase 2 (Pyk2) and Src family kinases, which in turn phosphorylates GluN2A-Tyr1325 residue of GluN2A-NMDARs to maintain channel activity. The continuity of this cycle of events leads to sustained Ca2+ influx through GluN2A-NMDAR. Our findings also show that lack of activation of the regulatory tyrosine phosphatase STEP, which can limit Pyk2 and Src family kinase activity further contributes to the maintenance of this cycle. Additional studies using live-cell imaging of neurons expressing a redox-sensitive GFP targeted to the mitochondrial matrix show that treatment with homocysteine leads to a progressive increase in mitochondrial reactive oxygen species generation, which is dependent on GluN2A-NMDAR-mediated sustained ERK MAPK activation. This later finding demonstrates a novel role of GluN2A-NMDAR in homocysteine-induced mitochondrial ROS generation and highlights the role of ERK MAPK as the intermediary signaling pathway between GluN2A-NMDAR stimulation and mitochondrial reactive oxygen species generation.

The outer membrane protein Tp92 of Treponema pallidum delays human neutrophil apoptosis via the ERK, PI3K/Akt, and NF-κB pathways

Syphilis is a persistent sexually transmitted disease caused by infiltration of the elusive pathogen Treponema pallidum. Despite the prevalence of human polymorphonuclear neutrophils (hPMNs) within cutaneous lesions, which are characteristic of incipient syphilis, their role in T. pallidum infection remains unclear. Tp92 is the only T. pallidum helical outer membrane protein that exhibits structural features similar to those of outer membrane proteins in other gram-negative bacteria. However, the functional mechanism of this protein in immune cells remains unclear. Neutrophils are short-lived cells that undergo innate apoptosis in response to external stimuli that typically influence this process. In this study, we determined that Tp92 impedes the activation of procaspase-3 via the ERK MAPK, PI3K/Akt, and NF-κB signaling pathways, consequently suppressing caspase-3 activity within hPMNs, and thereby preventing hPMNs apoptosis. Furthermore, Tp92 could also modulate hPMNs apoptosis by enhancing the expression of the anti-apoptotic protein Mcl-1, stimulating IL-8 secretion, and preserving the mitochondrial membrane potential. These findings provide valuable insights into the molecular mechanisms underlying T. pallidum infection and suggest potential therapeutic targets for syphilis treatment.

Signal transduction at GPCRs: Allosteric activation of the ERK MAPK by β-arrestin

β-arrestins are multivalent adaptor proteins that bind active phosphorylated G protein-coupled receptors (GPCRs) to inhibit G protein signaling, mediate receptor internalization, and initiate alternative signaling events. β-arrestins link agonist-stimulated GPCRs to downstream signaling partners, such as the c-Raf-MEK1-ERK1/2 cascade leading to ERK1/2 activation. β-arrestins have been thought to transduce signals solely via passive scaffolding by facilitating the assembly of multiprotein signaling complexes. Recently, however, β-arrestin 1 and 2 were shown to activate two downstream signaling effectors, c-Src and c-Raf, allosterically. Over the last two decades, ERK1/2 have been the most intensely studied signaling proteins scaffolded by β-arrestins. Here, we demonstrate that β-arrestins play an active role in allosterically modulating ERK kinase activity in vitro and within intact cells. Specifically, we show that β-arrestins and their GPCR-mediated active states allosterically enhance ERK2 autophosphorylation and phosphorylation of a downstream ERK2 substrate, and we elucidate the mechanism by which β-arrestins do so. Furthermore, we find that allosteric stimulation of dually phosphorylated ERK2 by active-state β-arrestin 2 is more robust than by active-state β-arrestin 1, highlighting differential capacities of β-arrestin isoforms to regulate effector signaling pathways downstream of GPCRs. In summary, our study provides strong evidence for a new paradigm in which β-arrestins function as active "catalytic" scaffolds to allosterically unlock the enzymatic activity of signaling components downstream of GPCR activation.

ACAGT-007a, an anti-cancer compound that modulates ERK MAPK signaling, induces nuclear enrichment of phosphorylated ERK in T3M4 pancreatic cancer cells

The extracellular-signal-regulated-kinase (ERK) signaling pathway is essential for cell proliferation and is frequently deregulated in human tumors such as pancreatic cancers. ACAGT-007a (GT-7), an anti-cancer compound, stimulates ERK phosphorylation, thereby inducing growth inhibition and apoptosis in T3M4 pancreatic cancer cells. However, how GT-7 stimulates ERK phosphorylation and induces apoptosis in ERK-active T3M4 cells remains unclear. To look into the mechanism, we performed a spatiotemporal analysis of ERK phosphorylation mediated by GT-7 in T3M4 cells. The immunoblotting showed that GT-7 stimulates ERK phosphorylation within 1 hr, which was more remarkable after 2 hr. Importantly, apoptosis induction as evaluated by the cleaved Caspase-3 was observed only after 2 hr incubation with GT-7. The immunofluorescence staining revealed the enrichment of phosphorylated ERK (phospho-ERK) in the nucleus upon 1 hr incubation with GT-7. Fractionation experiments showed that GT-7 increases phospho-ERK levels in the cytoplasm within 1 hr, whereas nuclear phospho-ERK accumulation is observed after 2 hr incubation with GT-7. MEK inhibition by U0126 significantly diminishes nuclear phospho-ERK distribution and apoptosis induction stimulated by GT-7. Thus, GT-7 may initiate the induction of ERK phosphorylation in the cytoplasm, which leads to phospho-ERK enrichment in the nucleus. This nuclear phospho-ERK accumulation by GT-7 precedes and may underlie apoptosis induction in T3M4.

Anti‑osteoclastogenic effects of Coriandrum sativum L. via the NF‑κB and ERK‑mediated NFATc1 signaling pathways

Coriandrum sativum L. (CSL) is an aromatic plant that belongs to the Apiaceae family. The present study aimed to determine the effects of the ethanol extract of the aerial part of CSL on osteoclast formation in vitro and in vivo, and the underlying molecular mechanism of its anti‑osteoclastogenic effect. The levels of osteoclast formation and bone resorption were evaluated by tartrate‑resistant acid phosphatase staining and bone resorption pit assays. The expression levels of osteoclast‑related molecules were analyzed by reverse transcription‑quantitative PCR and western blotting. The ethanol extract of CSL suppressed osteoclast formation in a mouse co‑culture system. In osteoblasts, CSL exerted a minor effect on the mRNA ratio of receptor activator of nuclear factor‑κB (NF‑κB) ligand (RANKL) to osteoprotegerin, suggesting a direct effect of CSL on osteoclast precursors. Notably, CSL inhibited RANKL‑induced osteoclast differentiation and bone resorption activity in bone marrow‑derived macrophage cultures. Mechanistically, CSL abolished RANKL‑induced NF‑κB and extracellular signal‑regulated kinase (ERK) MAPK activation, which effectively impaired the induction of c‑Fos and nuclear factor of activated T cells (NFATc1). Finally, the ethanol extract of CSL prevented osteoclast formation in a lipopolysaccharide‑induced calvarial bone loss model in vivo. The findings of the present study suggested that CSL may suppress osteoclast differentiation and function by downregulating the NF‑κB and ERK/c‑Fos/NFATc1 signaling pathways. Thus, CSL could be explored as a potential candidate for the prevention and treatment of osteolytic diseases.

ACAGT-007a, an ERK MAPK Signaling Modulator, in Combination with AKT Signaling Inhibition Induces Apoptosis in KRAS Mutant Pancreatic Cancer T3M4 and MIA-Pa-Ca-2 Cells

The mitogen-activated protein kinase (MAPK)/ERK and phosphatidylinositol-3 kinase (PI3K)/AKT pathways are dysregulated in various human cancers, including pancreatic ductal adenocarcinoma (PDAC), which has a very poor prognosis due to its lack of efficient therapies. We have previously identified ACAGT-007a (GT-7), an anti-cancer compound that kills ERK-active melanoma cells by inducing ERK-dependent apoptosis. Here, we investigated the apoptosis-inducing effect of GT-7 on three PDAC cell lines and its relevance with the MAPK/ERK and PI3K/AKT signaling pathways. GT-7 induced apoptosis in PDAC cells with different KRAS mutations (MIA-Pa-Ca-2 (KRAS G12C), T3M4 (KRAS Q61H), and PANC-1 (KRAS G12D)), being T3M4 most susceptible, followed by MIA-Pa-Ca-2, and PANC-1 was most resistant to apoptosis induction by GT-7. GT-7 stimulated ERK phosphorylation in the three PDAC cells, but only T3M4 displayed ERK-activation-dependent apoptosis. Furthermore, GT-7 induced a marked down-regulation of AKT phosphorylation after a transient peak in T3M4, whereas PANC-1 displayed the strongest and most sustained AKT activation, followed by MIA-Pa-Ca-2, suggesting that sustained AKT phosphorylation as a determinant for the resistance to GT-7-mediated apoptosis. Consistently, a PI3K inhibitor, Wortmannin, abolished AKT phosphorylation and enhanced GT-7-mediated apoptosis in T3M4 and MIA-Pa-Ca-2, but not in PANC-1, which showed residual AKT phosphorylation. This is the first report that ERK stimulation alone or in combination with AKT signaling inhibition can effectively induce apoptosis in PDAC and provides a rationale for a novel concurrent targeting of the PI3K/AKT and ERK pathways.

Hyperhomocysteinemia is an emerging comorbidity in ischemic stroke

Hyperhomocysteinemia or systemic elevation of the amino acid homocysteine is a common metabolic disorder that is considered to be a risk factor for ischemic stroke. However, it is still unclear whether predisposition to hyperhomocysteinemia could contribute to the severity of stroke outcome. This review highlights the advantages and limitations of the current rodent models of hyperhomocysteinemia, describes the consequence of mild hyperhomocysteinemia on the severity of ischemic brain damage in preclinical studies and summarizes the mechanisms involved in homocysteine induced neurotoxicity. The findings provide the premise for establishing hyperhomocysteinemia as a comorbidity for ischemic stroke and should be taken into consideration while developing potential therapeutic agents for stroke treatment.

Down-regulation of dual-specificity phosphatase 6, a negative regulator of oncogenic ERK signaling, by ACA-28 induces apoptosis in NIH/3T3 cells overexpressing HER2/ErbB2

Dual-specificity phosphatase 6 (DUSP6) is a key negative feedback regulator of the member of the RAS-ERK MAPK signaling pathway that is associated with cellular proliferation and differentiation. Deterioration of DUSP6 expression could therefore result in deregulated growth activity. We have previously discovered ACA-28, a novel anticancer compound with a unique property to stimulate ERK phosphorylation and induce apoptosis in ERK-active melanoma cells. However, the mechanism of cancer cell-specific-apoptosis by ACA-28 remains obscure. Here, we investigated the involvement of DUSP6 in the mechanisms of the ACA-28-mediated apoptosis by using the NIH/3T3 cells overexpressing HER2/ErbB2 (A4-15 cells), as A4-15 exhibited higher ERK phosphorylation and are more susceptible to ACA-28 than NIH/3T3. We showed that A4-15 exhibited high DUSP6 protein levels, which require ERK activation. Notably, the silencing of the DUDSP6 gene by siRNA inhibited proliferation and induced apoptosis in A4-15, but not in NIH/3T3, indicating that A4-15 requires high DUSP6 expression for growth. Importantly, ACA-28 preferentially down-regulated the DUSP6 protein and proliferation in A4-15 via the proteasome, while it stimulated ERK phosphorylation. Collectively, the up-regulation of DUSP6 may exert a growth-promoting role in cancer cells overexpressing HER2. DUSP6 down-regulation in ERK-active cancer cells might have the potential as a novel cancer measure.

Sprouty2 Inhibits Migration and Invasion of Fibroblast-Like Synoviocytes in Rheumatoid Arthritis by Down-regulating ATF2 Expression and Phosphorylation

Activating transcription factor 2(ATF2), a transcription factor belonging to the AP-1 family, plays an important role in inflammation. However, its biological functions and underlying molecular mechanisms in rheumatoid arthritis (RA) remain unclear. Western blot and immunohistochemistry were used to identify the expression of ATF2 and Sprouty2(SPRY2) in RA synovial tissues. SW982 cells were stimulated by TNF-α to establish an in vitro RA fibroblast-like synoviocyte (RA-FLS) model. Transwell and monolayer wound-healing were used to detect cell migration and invasion. RNA interference (si-ATF2) and adenovirus vector (Ad-SPRY2) methods were employed to manipulate ATF2 or SPRY2 expression in SW982 cells. The protein expression and phosphorylation levels in SW982 cells were evaluated by western blot. ATF2 expression and phosphorylation were upregulated in the RA synovial tissues. In RA-FLS model, ATF2 expression and phosphorylation were increased in a time-dependent manner. ATF2 knockdown inhibited the migration and invasion of RA-FLS model, reducing the inflammatory factors, which was consistent with the influence on cell behaviors caused by SPRY2 overexpression. Moreover, SPRY2 overexpression inhibited the TNF-α-induced phosphorylation of ERK and ATF2 in SW982 cells. The high expression and phosphorylation of ATF2 promoted migration and invasion of RA-FLSs. SPRY2 might inhibited the inflammatory responses of RA-FLSs via suppressing ERK-ATF2 pathway.

Discovery of new benzhydrol biscarbonate esters as potent and selective apoptosis inducers of human melanomas bearing the activated ERK pathway: SAR studies on an ERK MAPK signaling modulator, ACA-28

The recent discovery that an ERK signaling modulator [ACA-28 (2a)] preferentially kills human melanoma cell lines by inducing ERK-dependent apoptosis has generated significant interest in the field of anti-cancer therapy. In the first SAR study on 2a, here, we successfully developed candidates (2b, 2c) both of which induce more potent and selective apoptosis towards ERK-active melanoma cells than 2a, thus revealing the structural basis for inducing the ERK-dependent apoptosis and proposing the therapeutic prospect of these candidates against ERK-dependent cancers represented by melanoma.

ADAM17 selectively activates the IL-6 trans-signaling/ERK MAPK axis in KRAS-addicted lung cancer

Oncogenic KRAS mutations are major drivers of lung adenocarcinoma (LAC), yet the direct therapeutic targeting of KRAS has been problematic. Here, we reveal an obligate requirement by oncogenic KRAS for the ADAM17 protease in LAC In genetically engineered and xenograft (human cell line and patient-derived) Kras ^G12D-driven LAC models, the specific blockade of ADAM17, including with a non-toxic prodomain inhibitor, suppressed tumor burden by reducing cellular proliferation. The pro-tumorigenic activity of ADAM17 was dependent upon its threonine phosphorylation by p38 MAPK, along with the preferential shedding of the ADAM17 substrate, IL-6R, to release soluble IL-6R that drives IL-6 trans-signaling via the ERK1/2 MAPK pathway. The requirement for ADAM17 in Kras ^G12D-driven LAC was independent of bone marrow-derived immune cells. Furthermore, in KRAS mutant human LAC, there was a significant positive correlation between augmented phospho-ADAM17 levels, observed primarily in epithelial rather than immune cells, and activation of ERK and p38 MAPK pathways. Collectively, these findings identify ADAM17 as a druggable target for oncogenic KRAS-driven LAC and provide the rationale to employ ADAM17-based therapeutic strategies for targeting KRAS mutant cancers.

The role of heat shock protein 90 in regulating pain, opioid signaling, and opioid antinociception

Heat shock protein 90 (Hsp90) is one of the central signal transduction regulators of the cell. Via client interactions with hundreds of proteins, including receptors, receptor regulatory kinases, and downstream signaling regulators, Hsp90 has a crucial and wide-ranging impact on signaling in response to numerous drugs with impacts on resultant physiology and behavior. Despite this importance, however, Hsp90 has barely been studied in the context of pain and the opioid receptor system, leaving open the possibility that Hsp90 could be manipulated to improve pain therapeutic outcomes, a current area of massive medical need. In this review, we will highlight the known roles of Hsp90 in directly regulating the initiation and maintenance of the pain state. We will also explore how Hsp90 regulates signaling and antinociceptive responses to opioid analgesic drugs, with a special emphasis on ERK MAPK signaling. Understanding this new and growing area will improve our understanding of how Hsp90 regulates signaling and physiology, and also may provide new ways to treat pain, and perhaps reduce the severe impact of the ongoing opioid addiction and overdose crisis.

Hyperhomocysteinemia leads to exacerbation of ischemic brain damage: Role of GluN2A NMDA receptors

Hyperhomocysteinemia has been implicated in several neurodegenerative disorders including ischemic stroke. However, the pathological consequences of ischemic insult in individuals predisposed to hyperhomocysteinemia and the associated etiology are unknown. In this study, we evaluated the outcome of transient ischemic stroke in a rodent model of hyperhomocysteinemia, developed by subcutaneous implantation of osmotic pumps containing L-homocysteine into male Wistar rats. Our findings show a 42.3% mortality rate in hyperhomocysteinemic rats as compared to 7.7% in control rats. Magnetic resonance imaging of the brain in the surviving rats shows that mild hyperhomocysteinemia leads to exacerbation of ischemic injury within 24 h, which remains elevated over time. Behavioral studies further demonstrate significant deficit in sensorimotor functions in hyperhomocysteinemic rats compared to control rats. Using pharmacological inhibitors targeting the NMDAR subtypes, the study further demonstrates that inhibition of GluN2A-containing NMDARs significantly reduces ischemic brain damage in hyperhomocysteinemic rats but not in control rats, indicating that hyperhomocysteinemia-mediated exacerbation of ischemic brain injury involves GluN2A-NMDAR signaling. Complementary studies in GluN2A-knockout mice show that in the absence of GluN2A-NMDARs, hyperhomocysteinemia-associated exacerbation of ischemic brain injury is blocked, confirming that GluN2A-NMDAR activation is a critical determinant of the severity of ischemic damage under hyperhomocysteinemic conditions. Furthermore, at the molecular level we observe GluN2A-NMDAR dependent sustained increase in ERK MAPK phosphorylation under hyperhomocysteinemic condition that has been shown to be involved in homocysteine-induced neurotoxicity. Taken together, the findings show that hyperhomocysteinemia triggers a unique signaling pathway that in conjunction with ischemia-induced pathways enhance the pathology of stroke under hyperhomocysteinemic conditions.

PPARγ agonism attenuates cocaine cue reactivity

Cocaine use disorder is a chronic relapsing condition characterized by compulsive drug seeking and taking even after prolonged abstinence periods. Subsequent exposure to drug-associated cues can promote intense craving and lead to relapse in abstinent humans and rodent models. The responsiveness to these cocaine-related cues, or 'cue reactivity', can trigger relapse and cocaine-seeking behaviors; cue reactivity is measurable in cocaine-dependent humans as well as rodent models. Cue reactivity is thought to be predictive of cocaine craving and relapse. Here we report that PPARγ agonism during abstinence from cocaine self-administration reduced previously active lever pressing in Sprague Dawley rats during cue-reactivity tests, while administration of the PPARγ antagonist, GW9662, reversed this effect. PPARγ agonism also normalized nuclear ERK activity in the medial prefrontal cortex and hippocampus which was reversed with GW9662. Our results support the utility of PPARγ agonism as a relapse prevention strategy to maintain abstinence in the presence of cocaine-associated cues.

Role of AMPA receptors in homocysteine-NMDA receptor-induced crosstalk between ERK and p38 MAPK

Homocysteine, a metabolite of the methionine cycle has been reported to play a role in neurotoxicity through activation of N-methyl-d-aspartate receptors (NMDAR)-mediated signaling pathway. The proposed mechanisms associated with homocysteine-NMDAR-induced neurotoxicity involve a unique signaling pathway that triggers a crosstalk between extracellular signal-regulated kinase (ERK) and p38 MAPKs, where activation of p38 MAPK is downstream of and dependent on ERK MAPK. However, the molecular basis of the ERK MAPK-mediated p38 MAPK activation is not understood. This study investigates whether α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) play a role in facilitating the ERK MAPK-mediated p38 MAPK activation. Using surface biotinylation and immunoblotting approaches we show that treatment with homocysteine leads to a decrease in surface expression of GluA2-AMPAR subunit in neurons, but have no effect on the surface expression of GluA1-AMPAR subunit. Inhibition of NMDAR activation with D-AP5 or ERK MAPK phosphorylation with PD98059 attenuates homocysteine-induced decrease in surface expression of GluA2-AMPAR subunit. The decrease in surface expression of GluA2-AMPAR subunit is associated with p38 MAPK phosphorylation, which is inhibited by 1-napthyl acetyl spermine trihydrochloride (NASPM), a selective antagonist of GluA2-lacking Ca²⁺ -permeable AMPARs. These results suggest that homocysteine-NMDAR-mediated ERK MAPK phosphorylation leads to a decrease in surface expression of GluA2-AMPAR subunit resulting in Ca²⁺ influx through the GluA2-lacking Ca²⁺ -permeable AMPARs and p38 MAPK phosphorylation. Cell death assays further show that inhibition of AMPAR activity with 2,3-dioxo-6-nitro-1,2,3,4,tetrahydrobenzoquinoxaline-7-sulfonamide (NBQX)/6-cyano-7-nitroquinoxaline-2,3, -dione (CNQX) or GluA2-lacking Ca²⁺ -permeable AMPAR activity with NASPM attenuates homocysteine-induced neurotoxicity. We have identified an important mechanism involved in homocysteine-induced neurotoxicity that highlights the intermediary role of GluA2-lacking Ca²⁺ -permeable AMPARs in the crosstalk between ERK and p38 MAPKs.

Kidney injury molecule-1 (KIM-1) mediates renal epithelial cell repair via ERK MAPK signaling pathway

The expression of kidney injury molecule-1 (KIM-1), a very promising sensitive and specific urinary biomarker for acute renal injury, is markedly upregulated in injured and regenerating renal proximal tubular epithelial cells following ischemic or toxic insults, suggesting a possible role for this molecule in renal repair process. In the present study, we report that expression of KIM-1 facilitates renal tubular epithelial cell repair by promoting cell migration and proliferation. KIM-1 expression also enhances ERK MAPK activation, and the modulatory effect of KIM-1 on cellular repair process is likely mediated via ERK MAPK signaling pathway.

Intracellular signaling pathway regulation of myelination and remyelination in the CNS

The restoration of myelin sheaths on demyelinated axons remains a major obstacle in the treatment of multiple sclerosis (MS). Currently approved therapies work by modulating the immune system to reduce the number and rate of lesion formation but are only partially effective since they are not able to restore lost myelin. In the healthy CNS, myelin continues to be generated throughout life and spontaneous remyelination occurs readily in response to insults. In patients with MS, however, remyelination eventually fails, at least in part as a result of a failure of oligodendrocyte precursor cell (OPC) differentiation and the subsequent production of new myelin. A better understanding of the molecular mechanisms and signaling pathways that drive the process of myelin sheath formation is therefore important in order to speed the development of novel therapeutics designed to target remyelination. Here we review data supporting critical roles for three highly conserved intracellular signaling pathways: Wnt/β-catenin, PI3K/AKT/mTOR, and ERK/MAPK in the regulation of OPC differentiation and myelination both during development and in remyelination. Potential points of crosstalk between the three pathways and important areas for future research are also discussed.

Influence of Sex and ERK MAPK on the Pressure Reactivity Index in Newborn Piglets After Fluid Percussion Injury

Greater impairment in autoregulation is seen in male versus female piglets following fluid percussion injury (FPI). This is partially mediated by a greater upregulation of extracellular signal-related kinase mitogen-activated protein kinase (ERK MAPK). We hypothesized that these trends would be reflected by the pressure reactivity index (PRx), a clinical measure of autoregulation. We further hypothesized that PRx values would correlate well with pial artery dilatory responses to hypotension. Male and female piglets were subjected to FPI and treated with a vehicle or ERK MAPK antagonist U 0126 (1 mg/kg IV) 30 min post-injury. FPI led to upregulation of CSF ERK MAPK in untreated piglets of both sexes, however significantly higher PRx values were seen in male versus female piglets. Following administration of U 0126, elevation of ERK MAPK levels was blocked in both sexes and PRx values were significantly improved in the male. A strong correlation was seen between the PRx and pial artery vasomotor activity. These data support previous observations that male piglets demonstrate reversible ERK MAPK-mediated impairment in autoregulation following FPI, which is reflected by the PRx. The strong correlation between the PRx and pial artery vasomotor activity supports the practice of continuously monitoring cerebrovascular autoregulation in patients using this index.

Influence of Sex and ERK MAPK on the Pressure Reactivity Index in Newborn Piglets After Fluid Percussion Injury

Greater impairment in autoregulation is seen in male versus female piglets following fluid percussion injury (FPI). This is partially mediated by a greater upregulation of extracellular signal-related kinase mitogen-activated protein kinase (ERK MAPK). We hypothesized that these trends would be reflected by the pressure reactivity index (PRx), a clinical measure of autoregulation. We further hypothesized that PRx values would correlate well with pial artery dilatory responses to hypotension. Male and female piglets were subjected to FPI and treated with a vehicle or ERK MAPK antagonist U 0126 (1 mg/kg IV) 30 min post-injury. FPI led to upregulation of CSF ERK MAPK in untreated piglets of both sexes, however significantly higher PRx values were seen in male versus female piglets. Following administration of U 0126, elevation of ERK MAPK levels was blocked in both sexes and PRx values were significantly improved in the male. A strong correlation was seen between the PRx and pial artery vasomotor activity. These data support previous observations that male piglets demonstrate reversible ERK MAPK-mediated impairment in autoregulation following FPI, which is reflected by the PRx. The strong correlation between the PRx and pial artery vasomotor activity supports the practice of continuously monitoring cerebrovascular autoregulation in patients using this index.