Relationship between electroneurographic changes and serum ubiquitin levels in patients with type 2 diabetes

Post-ischemic cardioprotective potential of exogenous ubiquitin in myocardial remodeling late after ischemia/reperfusion injury

AIMS

Pretreatment with ubiquitin (UB) associates with preservation of heart function 3 days post-ischemia/reperfusion (I/R) injury. This study investigated the cardioprotective potential of exogenous UB late after myocardial I/R injury. To enhance the clinical relevance, UB treatment was started at the time of reperfusion and continued for 28 days post-I/R.

MAIN METHODS

Mice underwent ligation of the left anterior descending coronary artery for 45 min. At the time of reperfusion, mice were treated with UB or saline which was continued until 28 days post-I/R. Heart function was measured at 3, 7, 14 and 28 days post-I/R using echocardiography. Biochemical parameters of the heart and serum cytokines/chemokines levels were measured 28 days post-I/R.

KEY FINDINGS

I/R decreased heart function and induced LV dilation at all time points post-I/R. However, I/R + UB exhibited improved heart function throughout the observation period, while LV dilation was lower in I/R + UB group at 3, 14 and 28 days post-I/R. I/R-mediated increase in myocardial fibrosis, hypertrophy and apoptosis were significantly lower in I/R + UB vs. I/R. Collagen-1α1 and MMP-2 expression was lower, while MMP-9 and TIMP-2 expression was higher in I/R + UB vs. I/R. MYH-7B (hypertrophy marker) expression was lower in I/R + UB vs. I/R. GSK3β activation was lower (vs. Sham), while activation of ERK1/2 (vs. I/R) and AKT (vs. Sham) was higher in I/R + UB. Serum levels of IL-6, G-CSF and IL-2 were lower in I/R + UB vs. I/R.

SIGNIFICANCE

Post-ischemic UB treatment improves heart function, and associates with decreased myocardial fibrosis, apoptosis, hypertrophy and serum cytokine/chemokine levels.

Interferon regulatory factor 1‐triggered free ubiquitin protects the intestines against radiation‐induced injury via CXCR4/FGF2 signaling

Radiation‐induced intestinal injury is a serious concern during abdominal and pelvic cancers radiotherapy. Ubiquitin (Ub) is a highly conserved protein found in all eukaryotic cells. This study aims to explore the role and mechanism of free Ub against radiogenic intestinal injury. We found that free Ub levels of irradiated animals and human patients receiving radiotherapy were upregulated. Radiation‐induced Ub expression was associated with the activation of interferon regulatory factor 1 (IRF1). Intraperitoneal injection of free Ub significantly reduced the mortality of mice following 5–9 Gy total body irradiation (TBI) through the Akt pathway. Free Ub facilitates small intestinal regeneration induced by TBI or abdominal irradiation. At the cellular level, free Ub or its mutants significantly alleviated cell death and enhanced the survival of irradiated intestinal epithelial cells. The radioprotective role of free Ub depends on its receptor CXCR4. Mechanistically, free Ub increased fibroblast growth factor‐2 (FGF2) secretion and consequently activated FGFR1 signaling following radiation in vivo and in vivo. Thus, free Ub confers protection against radiation‐induced intestinal injury through CXCR4/Akt/FGF2 axis, which provides a novel therapeutic option.

Exogenous ubiquitin reduces inflammatory response and preserves myocardial function 3 days post-ischemia-reperfusion injury

β-Adrenergic receptor (β-AR) stimulation increases extracellular levels of ubiquitin (UB) in myocytes, and exogenous UB decreases β-AR-stimulated myocyte apoptosis and myocardial fibrosis. Here, we hypothesized that exogenous UB modulates the inflammatory response, thereby playing a protective role in cardiac remodeling after ischemia-reperfusion (I/R) injury. C57BL/6 mice infused with vehicle or UB (1 μg·g^-1·h^-1) were subjected to myocardial I/R injury. Functional and biochemical parameters of the heart were examined 3 days post-I/R. Heart weight-to-body weight ratios were similarly increased in I/R and UB + I/R groups. The area at risk and infarct size were significantly lower in UB + I/R versus I/R groups. Measurement of heart function using echocardiography revealed that I/R decreases percent fractional shortening and percent ejection fraction. However, the decrease in fractional shortening and ejection fraction was significantly lower in the UB + I/R group. The UB + I/R group displayed a significant decrease in inflammatory infiltrates, neutrophils, and macrophages versus the I/R group. Neutrophil activity was significantly lower in the UB + I/R group. Analysis of the concentration of a panel of 23 cytokines/chemokines in the serum using a Bio-Plex assay revealed a significantly lower concentration of IL-12 subunit p40 in the UB + I/R versus I/R group. The concentration of monocyte chemotactic protein-1 was lower, whereas the concentration of macrophage inflammatory protein-1α was significantly higher, in the UB+I/R group versus the sham group. Expression of matrix metalloproteinase (MMP)-2 and activity of MMP-9 were higher in the UB + I/R group versus the I/R group. Levels of ubiquitinated proteins and tissue inhibitor of metalloproteinase 2 expression were increased to a similar extent in both I/R groups. Thus, exogenous UB plays a protective role in myocardial remodeling post-I/R with effects on cardiac function, area at risk/infarct size, the inflammatory response, levels of serum cytokines/chemokines, and MMP expression and activity. NEW & NOTEWORTHY Stimulation of β-adrenergic receptors increases extracellular levels of ubiquitin (UB) in myocytes, and exogenous UB decreases β-adrenergic receptor-stimulated myocyte apoptosis and myocardial fibrosis. Here, we provide evidence that exogenous UB decreases the inflammatory response and preserves heart function 3 days after myocardial ischemia-reperfusion injury. Further identification of the molecular events involved in the anti-inflammatory role of exogenous UB may provide therapeutic targets for patients with ischemic heart disease.

Extracellular ubiquitin modulates cardiac fibroblast phenotype and function via its interaction with CXCR4

AIMS

β-adrenergic receptor (β-AR) stimulation increases extracellular levels of ubiquitin (UB), and exogenous UB plays an important role in β-AR-stimulated myocardial remodeling with effects on heart function, fibrosis and myocyte apoptosis. Cardiac fibroblasts are vital for maintaining the normal function of the heart, and in the structural remodeling of the heart in response to injury. Here we hypothesized that extracellular UB modulates cardiac fibroblast phenotype and function via its interaction with CXC chemokine receptor type 4 (CXCR4).

MAIN METHODS

Serum starved adult cardiac fibroblasts were used to identify CXCR4 as a receptor for UB. Fluorescent microscopy, co-immunoprecipitation, western blot, proliferation, migration and collagen contraction assays were performed to investigate the role of UB/CXCR4 axis on cell signaling, and modulation of fibroblast phenotype and function.

KEY FINDINGS

Using fluorescent microscopy and co-immunoprecipitation assay, we provide evidence that extracellular UB interacts with CXCR4. CXCR4 antagonist, AMD3100, inhibited interaction of UB with CXCR4. UB activated ERK1/2, not Akt. It enhanced VEGF-A expression, while decreasing β3 integrins expression. Two mutated UB proteins (V70A and F4A; unable to interact with CXCR4) failed to affect the expression of VEGF-A and β3 integrins. UB treatment inhibited migration of cells into the wound and FBS-stimulated cell proliferation. UB enhanced expression of α-smooth muscle actin (marker of myofibroblast differentiation) and contraction of fibroblast-populated collagen gel pads. Most of the effects of UB were negated by AMD3100.

SIGNIFICANCE

The data presented here suggest that UB interacts with CXCR4, and UB/CXCR4 interaction affects intracellular signaling, and modulates fibroblast phenotype and function.

Serum ubiquitin via CXC chemokine receptor 4 triggered cyclooxygenase-1 ubiquitination possibly involved in the pathogenesis of aspirin resistance

Extracellular ubiquitin (Ub) with platelet aggregation property was found higher in acute myocardial infarction (AMI) patients. Here we detected the platelet functions and serum Ub levels in 250 AMI patients and 50 healthy volunteers before and after aspirin treatment. The influence of serum Ub on platelet functions was determined in vitro. We found that 47 out of 250 AMI patients showed aspirin resistance (AR) and 203 showed aspirin sensitivity (AS). During hospitalization, AR group had higher serum Ub levels than the AS group or the healthy group, and the serum Ub levels was related to the rates of thrombosis events. The patients with higher serum Ub levels showed that the platelets had more ubiquitinated platelets, higher contents of ubiquitinated proteins and ubiquitinated cyclooxygenase-1 (COX-1). The levels of ubiquitinated COX-1 in the platelets was inversely correlated with acetylated COX-1, the separated ubiquitinated COX-1 activity was approximately twofold or fourfold higher than the total COX-1(ubiquitinated COX-1 and COX-1) or COX-1. In vitro, we found that extracellular Ub, via the CXC chemokine receptor 4 (CXCR4) pathway, facilitated COX-1 to be ubiquitined and prevented aspirin to acetylate its target. Platelets had higher levels of ubiquitinated COX-1 showing poor response to aspirin. Such results were not detected in Ub-free serum or ovalbumin incubated platelets. Serum Ub, via the CXCR4 pathway, facilitated COX-1 to be ubiquitined and activated the platelets possibly involved in the pathogenesis of AR.

Extracellular Ubiquitin: Role in Myocyte Apoptosis and Myocardial Remodeling

Ubiquitin (UB) is a highly conserved low molecular weight (8.5 kDa) protein. It consists of 76 amino acid residues and is found in all eukaryotic cells. The covalent linkage of UB to a variety of cellular proteins (ubiquitination) is one of the most common posttranslational modifications in eukaryotic cells. This modification generally regulates protein turnover and protects the cells from damaged or misfolded proteins. The polyubiquitination of proteins serves as a signal for degradation via the 26S proteasome pathway. UB is present in trace amounts in body fluids. Elevated levels of UB are described in the serum or plasma of patients under a variety of conditions. Extracellular UB is proposed to have pleiotropic roles including regulation of immune response, anti-inflammatory, and neuroprotective activities. CXCR4 is identified as receptor for extracellular UB in hematopoietic cells. Heart failure represents a major cause of morbidity and mortality in western society. Cardiac remodeling is a determinant of the clinical course of heart failure. The components involved in myocardial remodeling include-myocytes, fibroblasts, interstitium, and coronary vasculature. Increased sympathetic nerve activity in the form of norepinephrine is a common feature during heart failure. Acting via β-adrenergic receptor (β-AR), norepinephrine is shown to induce myocyte apoptosis and myocardial fibrosis. β-AR stimulation increases extracellular levels of UB in myocytes, and UB inhibits β-AR-stimulated increases in myocyte apoptosis and myocardial fibrosis. This review summarizes intracellular and extracellular functions of UB with particular emphasis on the role of extracellular UB in cardiac myocyte apoptosis and myocardial remodeling.

Extracellular ubiquitin increases expression of angiogenic molecules and stimulates angiogenesis in cardiac microvascular endothelial cells

Extracellular Ub is an immune modulator that plays a role in suppression of inflammation, organ injury, myocyte apoptosis, and fibrosis. The purpose of this study was to investigate the effects of extracellular Ub on the process of cardiac angiogenesis. CMECs and aortic tissue were isolated from rats to measure changes in angiogenic protein levels and to assess angiogenic responses to extracellular Ub. In CMECs, extracellular Ub increased protein levels of VEGF-A and MMP-2, known angiogenesis regulators. CMECs demonstrated enhanced rearrangement of fibrillar actin and migration in response to Ub treatment. Ub-treated CMECs demonstrated an increase in tube network formation which was inhibited by the CXCR4 receptor antagonist, AMD3100. Methylated Ub, unable to form polyubiquitin chains, enhanced tube network formation. Aortic ring sprouting assays demonstrated that Ub increases microvessel sprouting in the Matrigel. The results of our study suggest a novel role for extracellular Ub in cardiac angiogenesis, providing evidence that extracellular Ub, at least in part acting via the CXCR4 receptor, has the potential to facilitate the process of angiogenesis in myocardial endothelial cells.

Apo E gene polymorphism affects development of type 2 diabetic nephropathy in Asian populations, especially in East Asians: an updated meta-analysis

BACKGROUND

Many studies have determined the correlation between the Apolipoprotein E (APO E) gene polymorphisms and diabetic nephropathy, but their results are inconclusive.

MATERIAL/METHODS

With the aim to confirm this correlation, we performed a meta-analysis of 16 studies. The dichotomous data are presented as the odds ratio (OR) with a 95% confidence interval (CI).

RESULTS

The results of our study indicate that APO ε2 allele among the pooled Asian populations were more likely to show high risk of DN development (2 allele vs. ε3 allele: pooled OR =1.629, 95% CI=1.010-2.628, P=0.045). For further analysis, the APO e2 allele was associated with progress of DN in the group with duration >10 years, but not in the group with duration <10 years (ε2 allele vs. ε3 allele: pooled OR=1.920, 95% CI=1.338-2.754, P<0.001). The APO e2 polymorphism increased the susceptibility to DN in Asian population compared with healthy people (ε2 allele vs. ε3 allele: pooled OR=1.629, 95% CI=1.010-2.628, P=0.045).

CONCLUSIONS

Development of DN is associated with APO E polymorphisms in Asian populations, especially in East Asians.

MG132 ameliorates kidney lesions by inhibiting the degradation of Smad7 in streptozotocin-induced diabetic nephropathy

BACKGROUND

Smad7 is the main negative regulatory protein in the transforming growth factor-β (TGF-β) downstream signaling pathway, which plays an important role in diabetic nephropathy (DN) and may be related to the ubiquitin proteasome pathway (UPP).

AIM

We investigated the role of UPP in regulating TGF-β/SMAD signaling and explored the therapeutic effect of the ubiquitin proteasome inhibitor MG132 on DN.

METHODS

Wistar rats were randomly divided into a diabetes group and a normal control group. Rats in the diabetes group were injected intraperitoneally with streptozotocin. Diabetic rats were then randomly divided into a diabetic nephropathy group (DN group), an MG132 high concentration (MH) group, and an MG132 low concentration (ML) group. After 8 weeks of treatment, 24-hour urinary microalbumin (UAlb), urinary protein/urinary creatinine (Up/Ucr) values, ALT, AST, Bcr, kidney damage, TGF-β, Smad7, fibronectin (FN), and Smurf2 were detected.

RESULTS

The body mass and Smad7 protein expression decreased in DN group, but kidney weight, kidney weight index, UAlb, Up/Ucr, FN and Smurf2 mRNA expression, and TGF-β protein expression increased. However, these changes diminished following treatment with MG132, and a more pronounced effect was evident in MH group compared to ML group.

CONCLUSION

MG132 alleviates kidney damage by inhibiting Smad7 ubiquitin degradation and TGF-β activation in DN.

Exogenous ubiquitin modulates chronic β-adrenergic receptor-stimulated myocardial remodeling: role in Akt activity and matrix metalloproteinase expression

β-Adrenergic receptor (β-AR) stimulation increases extracellular ubiquitin (UB) levels, and extracellular UB inhibits β-AR-stimulated apoptosis in adult cardiac myocytes. This study investigates the role of exogenous UB in chronic β-AR-stimulated myocardial remodeling. l-Isoproterenol (ISO; 400 μg·kg(-1)·h(-1)) was infused in mice in the presence or absence of UB (1 μg·g(-1)·h(-1)). Left ventricular (LV) structural and functional remodeling was studied 7 days after infusion. UB infusion enhanced serum UB levels. In most parts, UB alone had no effect on morphometric or functional parameters. Heart weight-to-body weight ratios were increased to a similar extent in the ISO and UB + ISO groups. Echocardiographic analyses showed increased percent fractional shortening, ejection fraction, and LV circumferential stress and fiber-shortening velocity in the ISO group. These parameters were significantly lower in UB + ISO vs. ISO. Isovolumic contraction and relaxation times and ejection time were significantly lower in ISO vs. UB + ISO. The increase in the number of TUNEL-positive myocytes and fibrosis was significantly higher in ISO vs. UB + ISO. Activation of Akt was higher, whereas activation of GSK-3β and JNKs was lower in UB + ISO vs ISO. Expression of MMP-2, MMP-9, and TIMP-2 was higher in UB + ISO vs ISO. In isolated cardiac fibroblasts, UB enhanced expression of MMP-2 and TIMP-2 in the presence of ISO. Neutralizing UB antibodies negated the effects of UB on MMP-2 expression, whereas recombinant UB enhanced MMP-2 expression. UB activated Akt, and inhibition of Akt inhibited UB + ISO-mediated increases in MMP-2 expression. Thus, exogenous UB plays an important role in β-AR-stimulated myocardial remodeling with effects on LV function, fibrosis, and myocyte apoptosis.

Ubiquitination and proteolysis in acute lung injury

Ubiquitination is a posttranslational modification that regulates a variety of cellular functions depending on timing, subcellular localization, and type of tagging, as well as modulators of ubiquitin binding leading to proteasomal or lysosomal degradation or nonproteolytic modifications. Ubiquitination plays an important role in the pathogenesis of acute lung injury (ALI) and other lung diseases with pathologies secondary to inflammation, mechanical ventilation, and decreased physical mobility. Particularly, ubiquitination has been shown to affect alveolar epithelial barrier function and alveolar edema clearance by targeting the Na,K-ATPase and epithelial Na(+) channels upon lung injury. Notably, the proteasomal system also exhibits distinct functions in the extracellular space, which may contribute to the pathogenesis of ALI and other pulmonary diseases. Better understanding of these mechanisms may ultimately lead to novel therapeutic modalities by targeting elements of the ubiquitination pathway.

Extracellular ubiquitin: immune modulator and endogenous opponent of damage-associated molecular pattern molecules

Ubiquitin is a post-translational protein modifier and plays essential roles in all aspects of biology. Although the discovery of ubiquitin introduced this highly conserved protein as a molecule with extracellular actions, the identification of ubiquitin as the ATP-dependent proteolysis factor 1 has focused subsequent research on its important intracellular functions. Little attention has since been paid to its role outside of the cell. During recent years, multiple observations suggest that extracellular ubiquitin can modulate immune responses and that exogenous ubiquitin has therapeutic potential to attenuate exuberant inflammation and organ injury. These observations have not been integrated into a comprehensive assessment of its possible role as an endogenous immune modulator. This review recapitulates the current knowledge about extracellular ubiquitin and discusses an emerging facet of its role in biology during infectious and noninfectious inflammation. The synopsis of these data along with the recent identification of ubiquitin as a CXCR4 agonist suggest that extracellular ubiquitin may have pleiotropic roles in the immune system and functions as an endogenous opponent of DAMPs. Functions of extracellular ubiquitin could constitute an evolutionary conserved control mechanism aimed to balance the immune response and prevent exuberant inflammation. Further characterization of its mechanism of action and cellular signaling pathways is expected to provide novel insights into the regulation of the innate immune response and opportunities for therapeutic interventions.

Extracellular ubiquitin inhibits beta-AR-stimulated apoptosis in cardiac myocytes: role of GSK-3beta and mitochondrial pathways

AIMS

Beta-adrenergic receptor (beta-AR) stimulation induces apoptosis in adult rat ventricular myocytes (ARVMs) via the activation of glycogen synthase kinase-3beta (GSK-3beta) and mitochondrial pathways. However, beta-AR stimulation induces apoptosis only in a fraction ( approximately 15-20%) of ARVMs. We hypothesized that ARVMs may secrete/release a survival factor(s) which protects 80-85% of cells from apoptosis.

METHODS AND RESULTS

Using two-dimensional gel electrophoresis followed by MALDI TOF and MS/MS, we identified ubiquitin (Ub) in the conditioned media of ARVMs treated with beta-AR agonist (isoproterenol). Western blot analysis confirmed increased Ub levels in the conditioned media 3 and 6 h after beta-AR stimulation. Inhibition of beta1-AR and beta2-AR subtypes inhibited beta-AR-stimulated increases in extracellular levels of Ub, whereas activation of adenylyl cyclase using forskolin mimicked the effects of beta-AR stimulation. Incubation of cells with exogenous biotinylated Ub followed by western blot analysis of the cell lysates showed uptake of extracellular Ub into cells, which was found to be higher after beta-AR stimulation (1.9 +/- 0.4-fold; P < 0.05 vs. control, n = 6). Pre-treatment with Ub inhibited beta-AR-stimulated increases in apoptosis. Inhibition of phosphoinositide 3-kinase using wortmannin and LY-294002 prevented anti-apoptotic effects of extracellular Ub. Ub pre-treatment inhibited beta-AR-stimulated activation of GSK-3beta and c-Jun N-terminal kinase (JNK) and increases in the levels of cytosolic cytochrome c. The use of methylated Ub suggested that the anti-apoptotic effects of extracellular Ub are mediated via monoubiquitination.

CONCLUSION

beta-AR stimulation increases levels of Ub in the conditioned media. Extracellular Ub plays a protective role in beta-AR-stimulated apoptosis, possibly via the inactivation of GSK-3beta/JNK and mitochondrial pathways.

The roles of ubiquitin and 26S proteasome in human obesity

The ubiquitin-proteasome pathway is responsible for the degradation of most intracellular proteins in eukaryotes. It may also play a role in the modulation of inflammatory process and pathogenesis of cancer. Immunoglobulin levels are higher in cancer. Obesity is a risk factor for several common diseases, particularity type 2 diabetes mellitus, cardiovascular diseases, and tumors. The aim of this study was to study a possible correlation between plasma ubiquitin, 26S proteasome levels, and obesity. The body mass index (BMI), plasma ubiquitin levels, and 26S proteasome activity levels were determined and statistically analyzed in 31 volunteers, aged 19 to 58 years and including 9 men and 22 women, from the general population of Southern Taiwan. We also compared the immunoglobulin among the underweight, normal-weight, and overweight groups. We demonstrated that plasma ubiquitin is significantly decreased in obese individuals vs normal controls (65.2 +/- 23.4 vs 159.5 +/- 73.1 ng/mL). Plasma ubiquitin levels were found to be inversely correlated with the BMI of individuals (r = -0.39, P < .001). In addition, there was an inverse relationship between 20S proteasome levels in red blood cells and BMI (r = -0.33, P < .001), whereas 26S proteasome activity was found to be dependent quantitatively to S5a in erythrocytes (r = 0.88, P < .001). Immunoglobulin is significantly decreased in overweight individuals vs normal controls. Plasma ubiquitin and 20S proteasome levels are potential biomarkers for the risk assessment and possibly serve as one of the targeted studies for the development of human obesity.

Extracellular, circulating proteasomes and ubiquitin - incidence and relevance

The ubiquitin-proteasome system is the major pathway for intracellular protein degradation and is also deeply involved in the regulation of most basic cellular processes. Its proteolytic core, the 20S proteasome, has found to be attached also to the cell plasma membrane and certain observations are interpreted as to suggest that they may be released into the extracellular medium, e.g. in the alveolar lining fluid, epididymal fluid and possibly during the acrosome reaction. Proteasomes have also been detected in normal human blood plasma and designated circulating proteasomes; these have a comparatively low specific activity, a distinct pattern of subtypes and their exact origin is still enigmatic. In patients suffering from autoimmune diseases, malignant myeloproliferative syndromes, multiple myeloma, acute and chronic lymphatic leukaemia, solid tumour, sepsis or trauma, respectively, the concentration of circulating proteasomes has been found to be elevated, to correlate with the disease state and has even prognostic significance. Similarly, ubiquitin has been discovered as a normal component of human blood and seminal plasma and in ovarian follicular fluid. Increased concentrations were measured in diverse pathological situations, not only in blood plasma but also in cerebrospinal fluid, where it may have neuroprotective effects. As defective spermatozoa are covered with ubiquitin in the epididymal fluid, extracellular ubiquitination is proposed to be a mechanism for quality control in spermatogenesis. Growing evidence exists also for a participation of extracellular proteasomes and ubiquitin in the fertilization process.

Systemic ubiquitin release after blunt trauma and burns: association with injury severity, posttraumatic complications, and survival

BACKGROUND

Recent data suggest that ubiquitin (Ub) is systemically released after trauma, has pleiotropic effects on host defense mechanisms, and that Ub administration reduces fluid shifts into tissues during inflammation. Ub release after burns (B) has not been studied and its association with injury severity and outcome after blunt trauma (T) is unknown. Thus, we evaluated Ubs association with injury severity and outcomes after B and T.

METHODS

Injury severity was assessed with the Injury Severity Score (ISS) in T and burn size (% total body surface area, %TBSA) in B. A total of 129 T (ISS: 26 +/- 13) and 55 B (46% +/- 18% TBSA) were observed for sepsis/multiple organ failure (MOF) and survival. In B, sequential organ failure assessment scores were documented daily. Fifty volunteers served as controls (C) Ub serum levels were measured on day 0 (admission), 1, 3, 5, and 7 by enzyme-linked immunosorbent assay. Data were analyzed using bivariate or partial correlation analyses, t test, and analysis of variance with Tukey post-hoc test for multiple comparisons (two-tailed p < 0.05).

RESULTS

Ub was significantly elevated in patients. Peak levels (ng/mL) were detectable on day 0 (C: 118 +/- 76; T: 359 +/- 205; B: 573 +/- 331) and increased with increased ISS, %TBSA, and presence of inhalation injury. In T, Ub normalized by day 3, but remained elevated in B. In B, Ub correlated significantly negative with sequential organ failure assessment scores (r: -0.143; p = 0.0147), sepsis/MOF development (r: -0.363; p = 0.001), and survival (r: -0.231; p = 0.009). Compared with B who recovered uneventfully, Ub levels were significantly lower on days 1 to 7 and on days 5/7 in B who developed sepsis/MOF or died, respectively.

CONCLUSION

Ub concentrations reflect the extent of tissue damage. Along with Ubs previously described anti- inflammatory properties, this study suggests that its systemic release is protective, that burn patients who develop sepsis/MOF have a relative Ub deficiency and that Ub could play an important role during the physiologic response to burn injury.

Ubiquitin reduces contusion volume after controlled cortical impact injury in rats

Recent data suggest that ubiquitin has anti-inflammatory properties and therapeutic potential after severe trauma and brain injuries. However, direct evidence for its neuroprotective effects has not yet been provided. We hypothesized that ubiquitin treatment is neuroprotective, and thus reduces brain edema formation and cortical contusion volume after closed traumatic brain injuries. To test this hypothesis, a focal cortical contusion was induced using a controlled cortical impact (CCI) model in Sprague-Dawley rats. Animals (n = 27) were randomized to either 1.5 mg/kg ubiquitin or vehicle (placebo) intravenously within 5 min after CCI. Blood pressure, arterial blood gases (ABG) and intracranial pressure (ICP) were monitored. Ubiquitin serum and cerebrospinal fluid levels were measured by ELISA. Brain water content was quantified gravimetrically after 24 h and cerebral contusion volume was determined in triphenyltetrazolium-chloride stained brains after 7 days. All animals recovered to normal activity. ICP and cerebral perfusion pressures were normal at the end of the observation period. Ubiquitin serum and CSF levels at 24 h and 7 days after CCI were similar in both groups. With ubiquitin brain water content of the injured hemisphere was slightly lower (n = 6/group; 79.97 +/- 0.29% vs. 81.11 +/- 0.52%; p = 0.08). Cortical contusion volume was significantly lower with ubiquitin (n = 7-8/group; 32.88 +/- 2.1 mm(3) vs. 43.96 +/- 4.56 mm(3); p = 0.025). This study shows that ubiquitin treatment after brain injury has direct neuroprotective effects, as demonstrated by improved brain morphology 7 days after brain injury. In connection with its beneficial effects in our previous studies, these data suggest ubiquitin as a promising candidate protein therapeutic for the treatment of brain injuries.

Prolongation of skin graft survival by exogenous ubiquitin

Recently, it was shown that exogenous ubiquitin has anti-inflammatory actions in vivo and that the ubiquitin-decapeptide 50-59 has immunosuppressive effects similar to cyclosporine. Immunosuppressive effects of the native ubiquitin molecule and its therapeutic potential in transplantation are unknown. We tested the hypothesis that ubiquitin inhibits alloreactivity and increases allograft survival in a murine model of skin transplantation in fully mismatched strain combinations (C3H/HEJ-DBA2). Ubiquitin dose-dependently inhibited mixed leukocyte reaction in C3H/HEJ splenocytes in vitro. Intraperitoneal ubiquitin administration (25 microg/h for 14 days) was well-tolerated, dose-dependently increased ubiquitin serum concentrations and median allograft survival from 10 days (with albumin; control) to 17 days in DBA2 mice (survival ratio: 1.7, 95% confidence interval: 1.266-2.134; P=0.0005). The in vivo effects in this study combined with our previous work strongly indicate that ubiquitin is a potent immune modulator with broad therapeutic potential. Ubiquitin treatment could be a novel strategy to improve immunosuppressive regimens in transplantation.

Is insulin signaling molecules misguided in diabetes for ubiquitin-proteasome mediated degradation?

Recent mining of the human and mouse genomes, use of yeast genetics, and detailed analyses of several biochemical pathways, have resulted in the identification of many new roles for ubiquitin-proteasome mediated degradation of proteins. In the context of last year's award of Noble Prize (Chemistry) work, the ubiquitin and ubiquitin-like modifications are increasingly recognized as key regulatory events in health and disease. Although the ATP-dependent ubiquitin-proteasome system has evolved as premier cellular proteolytic machinery, dysregulation of this system by several different mechanisms leads to inappropriate degradation of specific proteins and pathological consequences. While aberrations in the ubiquitin-proteasome pathway have been implicated in certain malignancies and neurodegenerative disorders, recent studies indicate a role for this system in the pathogenesis of diabetes and its complications. Inappropriate degradation of insulin signaling molecules such as insulin receptor substrates (IRS-1 and IRS-2) has been demonstrated in experimental diabetes, mediated in part through the up-regulation of suppressors of cytokine signaling (SOCS). It appears that altered ubiquitin-proteasome system might be one of the molecular mechanisms of insulin resistance in many pathological situations. Drugs that modulate the SOCS action and/or proteasomal degradation of proteins could become novel agents for the treatment of insulin resistance and Type 2 diabetes.

Targeting the monocytic ubiquitin system with extracellular ubiquitin

Recent findings suggest that extracellular ubiquitin has pleiotropic effects on host defence mechanisms, but its cellular mechanism of action is not yet understood. Using fluorescence and in vivo confocal microscopy, we observed uptake of N-terminal fluorescein-labelled ubiquitin into human PBMC and MonoMac 6 cells. Immunoblotting experiments indicated that extracellular ubiquitin is then rapidly conjugated to a multitude of intracellular proteins. LPS and lipoteichoic acid significantly increased uptake and subsequent conjugation to intracellular proteins dose dependently. This mechanism showed saturation kinetics with a K(d) value for ubiquitin in the low nanomolar range (<10 nmol/L) and a B(max) value of 0.14-0.27 micromol ubiquitin/mg protein. These results suggest that the monocytic ubiquitin system can be targeted with physiologically relevant concentrations of extracellular ubiquitin during inflammation. This concept could provide a simple explanation for a multitude of extracellular ubiquitin's actions and open up new strategies to influence ubiquitin-dependent intracellular processes.

Ubiquitin reduces fluid shifts after traumatic brain injury

BACKGROUND

Ubiquitin has well-described intracellular properties. Recent data also suggest pleiotropic effects of extracellular ubiquitin, including induction of apoptosis, regulation of immune functions, and therapeutic potential during fluid resuscitation from severe trauma. However, the actions of exogenous ubiquitin after traumatic brain injury (TBI) are unknown.

METHODS

Series 1: Thirty-five minutes after TBI and hemorrhage, 1.5 mg ubiquitin/kg (n = 5) or albumin (n = 5) intravenous was followed by fluid resuscitation to maintain mean arterial and cerebral perfusion pressure. Series 2: Ubiquitin (n = 5) or vehicle (n = 6) was administered after TBI only. Ubiquitin was measured with enzyme-linked immunosorbent assay in serum, urine (series 1), and cerebrospinal fluid (series 2) for 300 minutes.

RESULTS

Series 1: After intravenous bolus, serum ubiquitin peaked at t = 45 minutes with a half-life of 54 minutes. Recovery in urine was 10%. With albumin versus ubiquitin, 85% more resuscitation fluid was required to stabilize systemic and cerebral hemodynamics (P < .05 for t = 150 to 300 minutes), but hematocrit was similar. With albumin there were progressive increases in intracranial pressure, peak inspiratory pressure, and decreases in oxygenation. All were significantly attenuated by ubiquitin (all P < .05 vs albumin). Series 2: Intravenous ubiquitin altered cerebrospinal fluid ubiquitin with an increased time to peak (t = 88 +/- 13 min vs 45 +/- 7 min, P < .05) and area under the concentration-time curve (82 +/- 22 vs 23 +/- 11 microg/min(1)/mL(-1), P < .05).

CONCLUSIONS

After TBI, intravenous ubiquitin crossed the blood-brain barrier and significantly reduced third spacing of fluid into the brain and lung during resuscitation.

Therapeutic potential of exogenous ubiquitin during resuscitation from severe trauma

BACKGROUND

Recent studies suggest that extracellular ubiquitin could have a physiologic role in immunodepression in sepsis and trauma. The therapeutic potential of exogenous ubiquitin after trauma has not been examined. To fill this gap, we designed a series of experiments in a clinically relevant trauma model.

METHODS

Forty minutes after femur fractures and hemorrhage, swine received 1.3 mg of ubiquitin per kilogram or bovine serum albumin intravenously followed by fluid resuscitation to maintain systemic hemodynamics. Leukocyte function and the immunomodulatory capacity of serum were assessed measuring endotoxin-evoked tumor necrosis factor-alpha (TNF alpha) production ex vivo. TNF alpha and ubiquitin were quantified with enzyme-linked immunosorbent assay.

RESULTS

Intravenous ubiquitin had no significant hemodynamic effect in normal animals. After injury, ubiquitin significantly reduced fluid requirements by at least 60% (p < 0.05). The injury was associated with transient immunodepression, as reflected by reduced endotoxin-evoked TNF alpha production by 40% to 50%. With ubiquitin, this response remained depressed for 100 to 160 minutes (p < 0.05), but fully recovered to baseline with albumin.

CONCLUSION

Ubiquitin is apparently safe and effective for reducing fluid requirements as a measure of diffuse capillary leak. This immunomodulatory property suggests a new therapeutic approach after injury in particular, and for infectious and noninfectious inflammation in general.

Extracellular ubiquitin inhibits the TNF-alpha response to endotoxin in peripheral blood mononuclear cells and regulates endotoxin hyporesponsiveness in critical illness

Ubiquitin is suggested to play a key role in essential intracellular functions, such as heat shock response, protein breakdown, and regulation of immune responses. Ubiquitin has also been detected in the extracellular space, but the function and biologic significance is unclear. We describe a new function of extracellular ubiquitin and show that extracellular ubiquitin specifically inhibits ex vivo secretion of tumor necrosis factor-alpha (TNF-alpha) and TNF-alpha mRNA expression from peripheral blood mononuclear cells (PBMNCs) in response to endotoxin in a dose-dependent manner. In contrast, the TNF-alpha response to zymosan or Staphylococcus aureus as well as the interleukin-6 (IL-6) and IL-8 responses to endotoxin were unaffected by ubiquitin. Measurement of serum ubiquitin levels showed a significant 5- to 7-fold increase in sepsis and trauma patients, to the level required for inhibition of the PBMNC TNF-alpha response to endotoxin by ubiquitin. Elevated ubiquitin levels in serum were significantly correlated with a reduced TNF-alpha production. Antibodies to ubiquitin were able to (1) significantly increase (2- to 5-fold) the TNF-alpha response to endotoxin in whole blood from trauma and sepsis patients, (2) completely neutralize the inhibitory effect of trauma patients' serum on healthy donors' TNF-alpha production, and (3) partially neutralize the inhibitory effect of sepsis patients' serum on healthy donors' TNF-alpha production. Ubiquitin-depleted serum from trauma patients lost the inhibitory activity for TNF-alpha production, whereas extracted endogenous ubiquitin exerts the inhibitory activity. The results demonstrate that extracellular ubiquitin acts as a cytokinelike protein with anti-inflammatory properties and indicate that extracellular ubiquitin is involved in the regulation of immunodepression in critical illness.

Isolation and functional analysis of mouse UbA52 gene and its relevance to diabetic nephropathy

In delineating the mechanism(s) of diabetic nephropathy various novel genes have been isolated, whereas others remain to be discovered. We identified several up-regulated genes in the kidneys of diabetic newborn mice. Among them was UbA52, a ubiquitin ribosomal fusion protein. Its mRNA expression in the kidney was proportional to blood glucose levels. By in situ hybridization and immunohistochemistry, UbA52 was exclusively localized to renal tubules, and its expression was markedly increased in diabetic mice. The up-regulated UbA52 mRNA and protein expression were also observed in Madin-Darby canine kidney cells, a tubular cell line, treated with 30 mm glucose in both cell lysates and ribosomal fractions. To explore the mechanism(s) of its increased expression, UbA52 genomic DNA was isolated. A transcription start site at -22 bp from the initiation codon was identified and confirmed by primer extension analysis. The UbA52 promoter region included glucose response-related E-box sequences and stress response elements (STRE). Unlike in humans, mouse UbA52 gene had no introns in the coding or 5'-ATG-flanking regions. To identify the DNA segment with maximal promoter activity, deletion constructs were prepared using a pSEAP vector system and transfected into COS7 kidney cells. Maximal activity was confined to -198 to +68 bp, which included E-boxes and STRE motifs. A dose-dependent increase in the promoter activity was observed in cells exposed to high glucose. Mutations in the first E-box (CAGCTG --> TGGCTG) or STRE (CCCCT --> CATCT) resulted in a decrease in the SEAP activity under high glucose ambience. Given the presence of glucose-responsive motifs in the promoter region and decrease in the SEAP activity in E-box mutants in the presence of glucose, these data suggest that UbA52, a ribosomal fusion protein, may be relevant in the pathogenesis of diabetic nephropathy.