Prophylactic versus endoscopy-driven treatment of Crohn's postoperative recurrence: A retrospective, multicentric European study (PORCSE study)

BACKGROUND AND AIMS

No consensus exists on optimal strategy to prevent postoperative recurrence (POR) after ileocecal resection (ICR) for Crohn's disease (CD).We compared early medical prophylaxis versus expectant management with treatment driven by findings at elective endoscopy 6-12 months after ICR.

METHODS

A retrospective, multicentric, observational study was performed. CD-patients undergoing first ICR were assigned to cohort1 if a biologic or immunomodulator was (re)started prophylactically after ICR, or to cohort2 if no postoperative prophylaxis was given and treatment was started as reaction to elective endoscopic findings. Primary endpoint was rate of endoscopic POR (Rutgeerts>i1). Secondary endpoints were severe endoscopic POR (Rutgeerts i3/i4), clinical POR, surgical POR and treatment burden during follow-up.

RESULTS

Of 346 included patients, 47.4% received prophylactic postoperative treatment (proactive/cohort1) and 52.6% did not (reactive/cohort2).Endoscopic POR (Rutgeerts>i1) rate was significantly higher in cohort2 (41.5% vs 53.8%, OR1.81, P=0.039) at endoscopy 6-12 months after surgery. No significant difference in severe endoscopic POR was found (OR1.29, P=0.517). Cohort2 had significantly higher clinical POR rates (17.7% vs 35.7%, OR3.05, P=0.002) and numerically higher surgical recurrence rates (6.7% vs 13.2%, OR2.59, P=0.051). Cox proportional hazards regression analysis showed no significant difference in time to surgical POR of proactive versus expectant/reactive approach (HR2.50, P=0.057). Quasi-Poisson regression revealed a significantly lower treatment burden for immunomodulator use in cohort2 (mean ratio 0.53, P=0.002), but no difference in burden of biologics or combination treatment.

CONCLUSIONS

The PORCSE study showed lower rates of endoscopic POR with early postoperative medical treatment compared to expectant management after first ileocecal resection for Crohn's disease.

Safety and Effectiveness of Vedolizumab and Ustekinumab in Elderly Patients with Inflammatory Bowel Disease: A Real-Life Multicentric Cohort Study

BACKGROUND

Data on ustekinumab and vedolizumab in the elderly inflammatory bowel disease (IBD) population are limited. The aim of the current study was to assess the safety and effectiveness of both in an elderly real-life population.

METHODS

A multicentric retrospective study was performed on IBD patients who started vedolizumab or ustekinumab between 2010 and 2020. Clinical and endoscopic remission rates and (serious) adverse events (AE) were assessed.

RESULTS

A total of 911 IBD patients were included, with 171 (19%) aged above 60 (111 VDZ, 60 UST). Elderly patients treated with vedolizumab or ustekinumab had an increased risk for non-IBD hospitalization (10.5% vs. 5.7%, p = 0.021) and malignancy (2.3% vs. 0.5%, p = 0.045) compared to the younger population. Corticosteroid-free clinical (50% vs. 44%; p = 0.201) and endoscopic remission rates (47.9% vs. 31%, p = 0.07) at 1 year were similar. Comparing vedolizumab to ustekinumab in the elderly population, corticosteroid-free (47.9% vs. 31%, p = 0.061) and endoscopic remission rates (66.7% vs. 64.4%, p = 0.981) were similar. Vedolizumab- and ustekinumab-treated patients had comparable infection rates (13.5% vs. 10.0%, p = 0.504), IBD flare-ups (4.5% vs. 5%, p = 1.000), the occurrence of new EIMs (13.5% vs. 10%, p = 0.504), a risk of intestinal surgery (5.4% vs. 6.7%, p = 0.742), malignancy (1.8% vs. 3.3%, p = 0.613), hospitalization (9.9% vs. 11.7%, p = 0.721), and mortality (0.9% vs. 1.7%, p = 1.000). AE risk was associated only with corticosteroid use.

CONCLUSIONS

Ustekinumab and vedolizumab show comparable effectiveness and safety in the elderly IBD population. Elderly IBD patients have an increased risk for non-IBD hospitalizations and malignancy compared to the younger IBD population, with corticosteroid use as the main risk factor.

A booster dose of SARS-COV-2 vaccine improves suboptimal seroconversion rates in patients with inflammatory bowel disease. Results of a prospective multicenter study of GETECCU (VACOVEII study)

BACKGROUND

The response to SARS-CoV-2 vaccination decreases in inflammatory bowel disease (IBD) patients, specially under anti-TNF treatment. However, data on medium-term effectiveness are limited, specially using new recommended seroconversion rate (>260BAU/mL). Our aim was to evaluate the 6-month>260 BAU-seroconversion rate after full vaccination and after booster-dose.

METHODS

VACOVEII is a Spanish multicenter, prospective study promoted by GETECCU. IBD patients full vaccinated against SARS-CoV-2 and without previous COVID-19 infection, treated or not with immunosuppressants, were included. The booster dose was administered 6 months after the full vaccination. Seroconversion was set at 260BAU/mL, according to most recent recommendations and was assessed 6 months after the full vaccination and 6 months after booster-dose.

RESULTS

Between October 2021 and March 2022, 313 patients were included (124 no treatment or mesalazine; 55 immunomodulators; 87 anti-TNF; 19 anti-integrin; and 28 ustekinumab). Most patients received mRNA-vaccines (86%). Six months after full vaccination, overall seroconversion rate was 44.1%, being significantly lower among patients on anti-TNF (19.5%, p<0.001) and ustekinumab (35.7%, p=0.031). The seroconversion rate after booster was 92%. Again, anti-TNF patients had a significantly lower seroconversion rate (67%, p<0.001). mRNA-vaccine improved seroconversion rate (OR 11.720 [95% CI 2.26-60.512]).

CONCLUSION

The full vaccination regimen achieves suboptimal response in IBD patients, specially among those anti-TNF or ustekinumab. The booster dose improves seroconversion rate in all patients, although it remains limited in those treated with anti-TNF. These results reinforce the need to prioritize future booster doses in patients on immunosuppressants therapy, specially under anti-TNF, and using mRNA-vaccines.

Pathogenic Mis-splicing of CPEB4 in Schizophrenia

BACKGROUND

Schizophrenia (SCZ) is caused by an interplay of polygenic risk and environmental factors, which may alter regulators of gene expression leading to pathogenic misexpression of SCZ risk genes. The CPEB family of RNA-binding proteins (CPEB1-4) regulates translation of target RNAs (approximately 40% of overall genes). We previously identified CPEB4 as a key dysregulated translational regulator in autism spectrum disorder (ASD) because its neuronal-specific microexon (exon 4) is mis-spliced in ASD brains, causing underexpression of numerous ASD risk genes. The genetic factors and pathogenic mechanisms shared between SCZ and ASD led us to hypothesize CPEB4 mis-splicing in SCZ leading to underexpression of multiple SCZ-related genes.

METHODS

We performed MAGMA-enrichment analysis on Psychiatric Genomics Consortium genome-wide association study data and analyzed RNA sequencing data from the PsychENCODE Consortium. Reverse transcriptase polymerase chain reaction and Western blot were performed on postmortem brain tissue, and the presence/absence of antipsychotics was assessed through toxicological analysis. Finally, mice with mild overexpression of exon 4-lacking CPEB4 (CPEB4Δ4) were generated and analyzed biochemically and behaviorally.

RESULTS

First, we found enrichment of SCZ-associated genes for CPEB4-binder transcripts. We also found decreased usage of CPEB4 microexon in SCZ probands, which was correlated with decreased protein levels of CPEB4-target SCZ-associated genes only in antipsychotic-free individuals. Interestingly, differentially expressed genes fit those reported for SCZ, specifically in the SCZ probands with decreased CPEB4-microexon inclusion. Finally, we demonstrated that mice with mild overexpression of CPEB4Δ4 showed decreased protein levels of CPEB4-target SCZ genes and SCZ-linked behaviors.

CONCLUSIONS

We identified aberrant CPEB4 splicing and downstream misexpression of SCZ risk genes as a novel etiological mechanism in SCZ.

The Impact of Vedolizumab and Ustekinumab on Articular Extra-Intestinal Manifestations in Inflammatory Bowel Disease Patients: A Real-Life Multicentre Cohort Study

BACKGROUND AND AIMS

Extra-intestinal manifestations are frequently reported in inflammatory bowel diseases. However, data comparing the effect of vedolizumab and ustekinumab on articular extra-intestinal manifestations are limited. The aim here was to evaluate differences in new-onset and the evolution of pre-existing joint extra-intestinal manifestations during both treatments.

METHODS

An international multicentre retrospective study was performed on inflammatory bowel disease patients who started vedolizumab or ustekinumab between May 2010 and December 2020. Extra-intestinal manifestations were assessed at baseline and joint extra-intestinal manifestations were evaluated throughout the 2-year follow-up. Arthropathy was defined by joint inflammation [arthritis/sacroiliitis], diagnosed by a rheumatologist, and arthralgia as articular pain without confirmed inflammation. Additionally, skin, ocular and hepatic extra-intestinal manifestations were assessed at baseline. Uni- and multivariate analyses were performed.

RESULTS

In total, 911 patients [vedolizumab: 584; ustekinumab: 327] were included. Deterioration of pre-existing arthropathy and rate of new-onset arthropathy were not significantly associated with vedolizumab over ustekinumab. Arthropathy was used as reason to stop treatment in six vedolizumab and two ustekinumab patients. The odds of developing new arthralgia within 6 months was higher in patients who took vedolizumab compared to ustekinumab (adjusted odds ratio [aOR]: 2.28 [1.01-5.15], p = 0.047). However, this effect was not sustained during the 2-year follow-up (aOR: 1.35 [0.80-2.29], p = 0.259). Deterioration of pre-existing arthralgia was comparable between ustekinumab and vedolizumab-treated patients. In two vedolizumab-treated patients arthralgia was given as the reason to stop treatment.

CONCLUSIONS

Vedolizumab and ustekinumab can be used safely in patients with articular extra-intestinal manifestations. Only a temporary increased risk for developing arthralgia has been observed under vedolizumab.

Management and Long-term Outcomes of Crohn's Disease Complicated with Enterocutaneous Fistula: ECUFIT Study from GETECCU

BACKGROUND AND AIMS

Crohn's disease [CD] can develop penetrating complications at any time during the disease course. Enterocutaneous fistulae [ECF] are disease-related complications with an important impact on quality of life. Our aim was to describe the outcomes of this complication, including its medical and/or surgical management and their temporal trends. The primary endpoint was fistula closure, defined as the absence of drainage, with no new abscess or surgery, over the preceding 6 months.

METHODS

Clinical information from all adult patients with CD and at least one ECF-excluding perianal fistulae-were identified from the prospectively-maintained ENEIDA registry. All additional information regarding treatment for this complication was retrospectively reviewed.

RESULTS

A total of 301 ECF in 286 patients [January 1970-September 2020] were analysed out of 30 088 records. These lesions were mostly located in the ileum [67%] and they had a median of one external opening [range 1-10]. After a median follow-up of 146 months (interquartile range [IQR], 69-233), 69% of patients underwent surgery. Fistula closure was achieved in 84%, mostly after surgery, and fistula recurrence was uncommon [13%]. Spontaneous and low-output fistulae were associated with higher closure rates (hazard ratio [HR] 1.51, 95% confidence interval [CI] 1.17-1.93, p = 0.001, and HR 1.49, 95% CI 1.07-2.06, p = 0.03, respectively); this was obtained more frequently with medical therapy since biologics have been available.

CONCLUSIONS

ECF complicating CD are rare but entail a high burden of medical and surgical resources. Closure rates are high, usually after surgery, and fistula recurrence is uncommon. A significant proportion of patients receiving medical therapy can achieve fistula closure.

CPEB alteration and aberrant transcriptome-polyadenylation lead to a treatable SLC19A3 deficiency in Huntington's disease

[Figure: see text].

Huntington's disease-specific mis-splicing unveils key effector genes and altered splicing factors

Correction of mis-splicing events is a growing therapeutic approach for neurological diseases such as spinal muscular atrophy or neuronal ceroid lipofuscinosis 7, which are caused by splicing-affecting mutations. Mis-spliced effector genes that do not harbour mutations are also good candidate therapeutic targets in diseases with more complex aetiologies such as cancer, autism, muscular dystrophies or neurodegenerative diseases. Next-generation RNA sequencing (RNA-seq) has boosted investigation of global mis-splicing in diseased tissue to identify such key pathogenic mis-spliced genes. Nevertheless, while analysis of tumour or dystrophic muscle biopsies can be informative on early stage pathogenic mis-splicing, for neurodegenerative diseases, these analyses are intrinsically hampered by neuronal loss and neuroinflammation in post-mortem brains. To infer splicing alterations relevant to Huntington’s disease pathogenesis, here we performed intersect-RNA-seq analyses of human post-mortem striatal tissue and of an early symptomatic mouse model in which neuronal loss and gliosis are not yet present. Together with a human/mouse parallel motif scan analysis, this approach allowed us to identify the shared mis-splicing signature triggered by the Huntington’s disease-causing mutation in both species and to infer upstream deregulated splicing factors. Moreover, we identified a plethora of downstream neurodegeneration-linked mis-spliced effector genes that—together with the deregulated splicing factors—become new possible therapeutic targets. In summary, here we report pathogenic global mis-splicing in Huntington’s disease striatum captured by our new intersect-RNA-seq approach that can be readily applied to other neurodegenerative diseases for which bona fide animal models are available.

P2X7 Receptor Upregulation in Huntington's Disease Brains

Huntington’s disease (HD) is a fatal degenerative disorder affecting the nervous system. It is characterized by motor, cognitive, and psychiatric dysfunctions, with a late onset and an autosomal dominant pattern of inheritance. HD-causing mutation consists in an expansion of repeated CAG triplets in the huntingtin gene (HTT), encoding for an expanded polyglutamine (polyQ) stretch in the huntingtin protein (htt). The mutation causes neuronal dysfunction and loss through multiple mechanisms, affecting both the nucleus and cytoplasm. P2X7 receptor (P2X7R) emerged as a major player in neuroinflammation, since ATP – its endogenous ligand – is massively released under this condition. Indeed, P2X7R stimulation in the central nervous system (CNS) is known to enhance the release of pro-inflammatory cytokines from microglia and of neurotransmitters from neuronal presynaptic terminals, as well as to promote apoptosis. Previous experiments performed with neurons expressing the mutant huntingtin and exploiting HD mouse models demonstrated a role of P2X7R in HD. On the basis of those results, here, we explore for the first time the status of P2X7R in HD patients’ brain. We report that in HD postmortem striatum, as earlier observed in HD mice, the protein levels of the full-length form of P2X7R, also named P2X7R-A, are upregulated. In addition, the exclusively human naturally occurring variant lacking the C-terminus region, P2X7R-B, is upregulated as well. As we show here, this augmented protein levels can be explained by elevated mRNA levels. Furthermore, in HD patients’ striatum, P2X7R shows not only an augmented total transcript level but also an alteration of its splicing. Remarkably, P2X7R introns 10 and 11 are more retained in HD patients when compared with controls. Taken together, our data confirm that P2X7R is altered in brains of HD subjects and strengthen the notion that P2X7R may represent a potential therapeutic target for HD.

Early treatment with anti-tumor necrosis factor agents improves long-term effectiveness in symptomatic stricturing Crohn's disease

BACKGROUND

There is limited evidence on the effectiveness of biological therapy in stricturing complications in patients with Crohn's disease.

AIM

The study aims to determine the effectiveness of anti-tumor necrosis factor (TNF) agents in Crohn's disease complicated with symptomatic strictures.

METHODS

In this multicentric and retrospective study, we included adult patients with symptomatic stricturing Crohn's disease receiving their first anti-TNF therapy, with no previous history of biological, endoscopic or surgical therapy. The effectiveness of the anti-TNF agent was defined as a composite outcome combining steroid-free drug persistence with no use of new biologics or immunomodulators, hospital admission, surgery or endoscopic therapy during follow-up.

RESULTS

Overall, 262 patients with Crohn's disease were included (53% male; median disease duration, 35 months, 15% active smokers), who received either infliximab (N = 141, 54%) or adalimumab (N = 121, 46%). The treatment was effective in 87% and 73% of patients after 6 and 12 months, respectively, and continued to be effective in 26% after a median follow-up of 40 months (IQR, 19-85). Nonetheless, 15% and 21% of individuals required surgery after 1 and 2 years, respectively, with an overall surgery rate of 32%. Postoperative complications were identified in 15% of patients, with surgical site infection as the most common. Starting anti-TNF therapy in the first 18 months after the diagnosis of Crohn's disease or the identification of stricturing complications was associated with a higher effectiveness (HR 1.62, 95% CI 1.18-2.22; and HR 1.55, 95% CI 1.1-2.23; respectively). Younger age, lower albumin levels, strictures located in the descending colon, concomitant aminosalicylates use or presence of lymphadenopathy were associated with lower effectiveness.

CONCLUSIONS

Anti-TNF agents are effective in approximately a quarter of patients with Crohn's disease and symptomatic intestinal strictures, and 68% of patients are free of surgery after a median of 40 months of follow-up. Early treatment and some potential predictors of response were associated with treatment success in this setting.

Tacrolimus induces short-term but not long-term clinical response in inflammatory bowel disease

BACKGROUND

Tacrolimus is a calcineurin inhibitor commonly used for prophylaxis of rejection in renal and liver transplantation. There are limited but favourable data regarding its possible use in patients with inflammatory bowel disease (IBD).

AIMS

To evaluate the efficacy and safety of tacrolimus in patients with IBD in clinical practice.

METHODS

We performed a retrospective, multicentre study in 22 centres in Spain. All adult patients who received oral tacrolimus for luminal or perianal IBD were included. Clinical response was assessed by Harvey-Bradshaw index and partial Mayo score after 3 months. Perianal disease was evaluated by fistula drainage assessment.

RESULTS

One hundred and forty-three patients were included (mean age 38 years; 51% male; median disease duration 110 months). In ulcerative colitis (UC) (n = 58), the partial Mayo score decreased after 3 months from median 6 to 3 (P = 0.0001), whereas in Crohn's disease (CD) (n = 85), the Harvey-Bradshaw index decreased after 3 months from median 9 to 7 (P = 0.011). In CD patients, blood tacrolimus concentrations during induction (>10 ng/mL vs <10 ng/mL; odds ratio 0.23, 95% CI 0.05-0.87) and the concomitant use of thiopurines (odds ratio 0.18, 95% CI 0.04-0.81) were associated with lower clinical disease activity at 3 months. Of 62 patients with perianal disease, complete closure was observed in 8% (n = 5) of patients with perianal fistulas, with 34% (n = 21) showing partial response. Treatment was maintained for a median of 6 months (IQR, 2-16). After a median clinical follow-up of 24 months (IQR, 15-57), the rate of treatment-related adverse events was 34%, correlating with blood drug concentrations (P = 0.021). Finally, 120 patients (84%) discontinued tacrolimus, usually due to absence or loss of response. Three patients (2%) were subsequently diagnosed with cancer. The overall rate of surgery was 39%, with a 33% colectomy rate in UC.

CONCLUSIONS

Tacrolimus shows a clinical benefit in both CD and UC after 3 months of treatment, but its long-term effectiveness and frequent adverse events remain relevant issues in clinical practice.

Usefulness of magnetic resonance enterography in the clinical decision-making process for patients with inflammatory bowel disease

OBJECTIVE

To evaluate the impact of magnetic resonance enterography (MRE) diagnosis on clinical decision-making regarding treatment choice and maintenance of treatment over time in patients with inflammatory bowel disease (IBD).

METHODS

A cohort of patients who underwent MRE for IBD assessment between 2011 and 2014 was analyzed. From clinical records, we retrospectively retrieved their demographic data and clinical data on their IBD at the time of MRE, the results of MRE and the patient's clinical course. Medical management decisions made during the three months following MRE and at the 15-month follow-up were assessed.

RESULTS

In total, 474 MREs were reviewed. In the first three-month period, MRE results led to changes in the medical management of 266 patients (56.1%). Of those, maintenance therapy was altered in 140 patients (68.3%) (90.7% step-up and 9.3% top-down strategy), 65 (24.4%) were prescribed a course of steroids and 61 (22.9%) underwent surgery. MRE confirmed a CD diagnosis in 14/41 patients (34.1%) previously diagnosed with indeterminate colitis or ulcerative colitis and in 4/18 patients (22.2%) with suspected IBD. At the 15-month follow-up, treatment remained unchanged in 289 patients (65.8%).

CONCLUSIONS

These results suggest that MRE is a diagnostic tool that provides valid information for the clinical-decision making process for patients with CD.

HIF1α Suppresses Tumor Cell Proliferation through Inhibition of Aspartate Biosynthesis

Cellular aspartate drives cancer cell proliferation, but signaling pathways that rewire aspartate biosynthesis to control cell growth remain largely unknown. Hypoxia-inducible factor-1α (HIF1α) can suppress tumor cell proliferation. Here, we discovered that HIF1α acts as a direct repressor of aspartate biosynthesis involving the suppression of several key aspartate-producing proteins, including cytosolic glutamic-oxaloacetic transaminase-1 (GOT1) and mitochondrial GOT2. Accordingly, HIF1α suppresses aspartate production from both glutamine oxidation as well as the glutamine reductive pathway. Strikingly, the addition of aspartate to the culture medium is sufficient to relieve HIF1α-dependent repression of tumor cell proliferation. Furthermore, these key aspartate-producing players are specifically repressed in VHL-deficient human renal carcinomas, a paradigmatic tumor type in which HIF1α acts as a tumor suppressor, highlighting the in vivo relevance of these findings. In conclusion, we show that HIF1α inhibits cytosolic and mitochondrial aspartate biosynthesis and that this mechanism is the molecular basis for HIF1α tumor suppressor activity.

Autism-like phenotype and risk gene mRNA deadenylation by CPEB4 mis-splicing

Common genetic contributions to autism spectrum disorder (ASD) reside in risk gene variants that individually have minimal effect sizes. As environmental factors that perturb neurodevelopment also underlie idiopathic ASD, it is crucial to identify altered regulators that can orchestrate multiple ASD risk genes during neurodevelopment. Cytoplasmic polyadenylation element binding proteins 1-4 (CPEB1-4) regulate the translation of specific mRNAs by modulating their poly(A)-tails and thereby participate in embryonic development and synaptic plasticity. Here we find that CPEB4 binds transcripts of most high-confidence ASD risk genes. The brains of individuals with idiopathic ASD show imbalances in CPEB4 transcript isoforms that result from decreased inclusion of a neuron-specific microexon. In addition, 9% of the transcriptome shows reduced poly(A)-tail length. Notably, this percentage is much higher for high-confidence ASD risk genes, correlating with reduced expression of the protein products of ASD risk genes. An equivalent imbalance in CPEB4 transcript isoforms in mice mimics the changes in mRNA polyadenylation and protein expression of ASD risk genes and induces ASD-like neuroanatomical, electrophysiological and behavioural phenotypes. Together, these data identify CPEB4 as a regulator of ASD risk genes.

HIF2α acts as an mTORC1 activator through the amino acid carrier SLC7A5

The mammalian target of rapamycin (mTOR) pathway, which is essential for cell proliferation, is repressed in certain cell types in hypoxia. However, hypoxia-inducible factor 2α (HIF2α) can act as a proliferation-promoting factor in some biological settings. This paradoxical situation led us to study whether HIF2α has a specific effect on mTORC1 regulation. Here we show that activation of the HIF2α pathway increases mTORC1 activity by upregulating expression of the amino acid carrier SLC7A5. At the molecular level we also show that HIF2α binds to the Slc7a5 proximal promoter. Our findings identify a link between the oxygen-sensing HIF2α pathway and mTORC1 regulation, revealing the molecular basis of the tumor-promoting properties of HIF2α in von Hippel-Lindau-deficient cells. We also describe relevant physiological scenarios, including those that occur in liver and lung tissue, wherein HIF2α or low-oxygen tension drive mTORC1 activity and SLC7A5 expression.

Induction of the mitochondrial NDUFA4L2 protein by HIF-1α decreases oxygen consumption by inhibiting Complex I activity

The fine regulation of mitochondrial function has proved to be an essential metabolic adaptation to fluctuations in oxygen availability. During hypoxia, cells activate an anaerobic switch that favors glycolysis and attenuates the mitochondrial activity. This switch involves the hypoxia-inducible transcription factor-1 (HIF-1). We have identified a HIF-1 target gene, the mitochondrial NDUFA4L2 (NADH dehydrogenase [ubiquinone] 1 alpha subcomplex, 4-like 2). Our results, obtained employing NDUFA4L2-silenced cells and NDUFA4L2 knockout murine embryonic fibroblasts, indicate that hypoxia-induced NDUFA4L2 attenuates mitochondrial oxygen consumption involving inhibition of Complex I activity, which limits the intracellular ROS production under low-oxygen conditions. Thus, reducing mitochondrial Complex I activity via NDUFA4L2 appears to be an essential element in the mitochondrial reprogramming induced by HIF-1.

Acute Vhl gene inactivation induces cardiac HIF-dependent erythropoietin gene expression

Von Hippel Lindau (Vhl) gene inactivation results in embryonic lethality. The consequences of its inactivation in adult mice, and of the ensuing activation of the hypoxia-inducible factors (HIFs), have been explored mainly in a tissue-specific manner. This mid-gestation lethality can be also circumvented by using a floxed Vhl allele in combination with an ubiquous tamoxifen-inducible recombinase Cre-ER^T2. Here, we characterize a widespread reduction in Vhl gene expression in Vhl^floxed-UBC-Cre-ER^T2 adult mice after dietary tamoxifen administration, a convenient route of administration that has yet to be fully characterized for global gene inactivation. Vhl gene inactivation rapidly resulted in a marked splenomegaly and skin erythema, accompanied by renal and hepatic induction of the erythropoietin (Epo) gene, indicative of the in vivo activation of the oxygen sensing HIF pathway. We show that acute Vhl gene inactivation also induced Epo gene expression in the heart, revealing cardiac tissue to be an extra-renal source of EPO. Indeed, primary cardiomyocytes and HL-1 cardiac cells both induce Epo gene expression when exposed to low O₂ tension in a HIF-dependent manner. Thus, as well as demonstrating the potential of dietary tamoxifen administration for gene inactivation studies in UBC-Cre-ER^T2 mouse lines, this data provides evidence of a cardiac oxygen-sensing VHL/HIF/EPO pathway in adult mice.

Myeloid hypoxia-inducible factors in inflammatory diseases

Hypoxia inducible factors (HIF1 and HIF2) have emerged as central regulators of the activity of myeloid cells at inflammatory sites where O(2) is frequently limited. Novel insights in the field have revealed that the expression of HIFs by myeloid cells is not exclusively induced by hypoxia but also in response to central inflammatory mediators independently of O(2) shortage. This has substantially elevated the biological significance of HIFs in the context of inflammatory diseases. As a consequence, the loss of HIF1 or HIF2 in myeloid cells specifically compro-mises some of the processes driven by myeloid cells, such as bactericidal activity and myeloid invasion, as well as inflammation-associated detrimental consequences.

Macrophage oxygen sensing modulates antigen presentation and phagocytic functions involving IFN-gamma production through the HIF-1 alpha transcription factor

Low oxygen tension areas are found in inflamed or diseased tissues where hypoxic cells induce survival pathways by regulating the hypoxia-inducible transcription factor (HIF). Macrophages are essential regulators of inflammation and, therefore, we have analyzed their response to hypoxia. Murine peritoneal elicited macrophages cultured under hypoxia produced higher levels of IFN-gamma and IL-12 mRNA and protein than those cultured under normoxia. A similar IFN-gamma increment was obtained with in vivo models using macrophages from mice exposed to atmospheric hypoxia. Our studies showed that IFN-gamma induction was mediated through HIF-1alpha binding to its promoter on a new functional hypoxia response element. The requirement of HIF-alpha in the IFN-gamma induction was confirmed in RAW264.7 cells, where HIF-1alpha was knocked down, as well as in resident HIF-1alpha null macrophages. Moreover, Ag presentation capacity was enhanced in hypoxia through the up-regulation of costimulatory and Ag-presenting receptor expression. Hypoxic macrophages generated productive immune synapses with CD8 T cells that were more efficient for activation of TCR/CD3epsilon, CD3zeta and linker for activation of T cell phosphorylation, and T cell cytokine production. In addition, hypoxic macrophages bound opsonized particles with a higher efficiency, increasing their phagocytic uptake, through the up-regulated expression of phagocytic receptors. These hypoxia-increased immune responses were markedly reduced in HIF-1alpha- and in IFN-gamma-silenced macrophages, indicating a link between HIF-1alpha and IFN-gamma in the functional responses of macrophages to hypoxia. Our data underscore an important role of hypoxia in the activation of macrophage cytokine production, Ag-presenting activity, and phagocytic activity due to an HIF-1alpha-mediated increase in IFN-gamma levels.

Three different genes encode the iron-sulfur subunit of succinate dehydrogenase in Arabidopsis thaliana

The iron-sulfur protein is an essential component of mitochondrial complex II (succinate dehydrogenase, SDH), which is a functional enzyme of both the citric acid cycle and the respiratory electron transport chain. This protein is encoded by a single-copy nuclear gene in mammals and fungi and by a mitochondrial gene in Rhodophyta and the protist Reclinomonas americana. In Arabidopsis thaliana, the homologous protein is now found to be encoded by three nuclear genes. Two genes (sdh2-1 and sdh2-2) likely arose from a relatively recent duplication event since they have similar structures, encode nearly identical proteins and show similar expression patterns. Both genes are interrupted by a single intron located at a conserved position. Expression was detected in all tissues analysed, with the highest steady-state mRNA levels found in flowers and inflorescences. In contrast, the third gene (sdh2-3) is interrupted by 4 introns, is expressed at a low level, and encodes a SDH2-3 protein which is only 67% similar to SDH2-1 and SDH2-2 and has a different N-terminal presequence. Interestingly, the proteins encoded by these three genes are probably functional because they are highly conserved compared with their homologues in other organisms. These proteins contain the cysteine motifs involved in binding the three iron-sulfur clusters essential for electron transport. Furthermore, the three polypeptides are found to be imported into isolated plant mitochondria.

Agonist-dependent modulation of G protein-coupled receptor kinase 2 by mitogen-activated protein kinases

A variety of G protein-coupled receptors (GPCRs) are phosphorylated by G protein-coupled receptor kinase 2 (GRK2). This event promotes the binding of regulatory proteins termed beta-arrestins to GPCRs, leading to uncoupling from G proteins and receptor internalization. Recent data indicate that GRK2 and beta-arrestins also play an important role in the stimulation of the extracellular signal-regulated kinases (ERK)/mitogen-activated protein kinase (MAPK) cascade by GPCRs. In this report, we have investigated the existence of functional interactions between GRK2 and MAPK. We show that activation of beta(2)-adrenergic receptors (beta(2)-AR) promotes the rapid association of GRK2 and MAPK in living cells, as assessed by coimmunoprecipitation experiments in COS-7 cells transfected with beta(2)-AR, GRK2, and an epitope-tagged MAPK. Coimmunoprecipitation of MAPK and GRK2 is blocked by inhibition of the MAPK cascade and is not observed upon activation of MAPK in the absence of beta(2)-AR stimulation, thus indicating that both an active MAPK and agonist occupancy of GPCR are required for the association to occur. Interestingly, we have found that purified ERK1/MAPK can directly phosphorylate the C-terminal domain of GRK2, and that the phosphorylation process is favored by the presence of Gbetagamma-subunits or an activated receptor. Furthermore, GRK2 phosphorylation by MAPK leads to a decreased activity of GRK2 toward GPCR. Taken together, our results suggest that stimulation of GPCRs promotes the rapid association of GRK2 and MAPK leading to modulation of GRK2 functionality, thus putting forward a new feedback mechanism for the regulation of GPCR signaling.

Agonist-dependent phosphorylation of the G protein-coupled receptor kinase 2 (GRK2) by Src tyrosine kinase

GRK2 is a member of the G protein-coupled receptor kinase (GRK) family, which phosphorylates the activated form of a variety of G protein-coupled receptors (GPCR) and plays an important role in GPCR modulation. It has been recently reported that stimulation of the mitogen-activated protein kinase cascade by GPCRs involves tyrosine phosphorylation of docking proteins mediated by members of the Src tyrosine kinase family. In this report, we have investigated the possible role of c-Src in modulating GRK2 function. We demonstrate that c-Src can directly phosphorylate GRK2 on tyrosine residues, as shown by in vitro experiments with purified proteins. The phosphorylation reaction exhibits an apparent K(m) for GRK2 of 12 nM, thus suggesting a physiological relevance in living cells. Consistently, overexpression of the constitutively active c-Src Y527F mutant in COS-7 cells leads to tyrosine phosphorylation of co-expressed GRK2. In addition, GRK2 can be detected in phosphotyrosine immunoprecipitates from HEK-293 cells transiently transfected with this Src mutant. Interestingly, phosphotyrosine immunoblots reveal a rapid and transient increase in GRK2 phosphorylation upon agonist stimulation of beta(2)-adrenergic receptors co-transfected with GRK2 and wild type c-Src in COS-7 cells. This tyrosine phosphorylation is maximal within 5 min of isoproterenol stimulation and reaches values of approximately 5-fold over basal conditions. Furthermore, GRK2 phosphorylation on tyrosine residues promotes an increased kinase activity toward its substrates. Our results suggest that GRK2 phosphorylation by c-Src is inherent to GPCR activation and put forward a new mechanism for the regulation of GPCR signaling.

G protein-coupled receptor kinase 2 (GRK2): mechanisms of regulation and physiological functions

G protein-coupled receptor kinase 2 (GRK2) plays a key role in determining the rate and extent of G protein-coupled receptor (GPCR) desensitization and resensitization. Recent data indicate that GRK2 activity, subcellular distribution and expression are tightly regulated. The important physiological function of GRK2 as a modulator of the efficacy of GPCR signal transduction systems is exemplified by its relevance in cardiovascular physiopathology as well as by its emerging role in the regulation of chemokine receptors.