Succinate Dehydrogenase Mutations Research Articles

Metabolomics for the design of new metabolic engineering strategies for improving aerobic succinic acid production in Escherichia coli

IntroductionGlycerol is a byproduct from the biodiesel industry that can be biotransformed by Escherichia coli to high added-value products such as succinate under aerobic conditions. The main genetic engineering strategies to achieve this aim involve the mutation of succinate dehydrogenase (sdhA) gene and also those responsible for acetate synthesis including acetate kinase, phosphate acetyl transferase and pyruvate oxidase encoded by ackA, pta and pox genes respectively in the ΔsdhAΔack-ptaΔpox (M4) mutant. Other genetic manipulations to rewire the metabolism toward succinate consist on the activation of the glyoxylate shunt or blockage the pentose phosphate pathway (PPP) by deletion of isocitrate lyase repressor (iclR) or gluconate dehydrogenase (gnd) genes on M4-ΔiclR and M4-Δgnd mutants respectively.ObjectiveTo deeply understand the effect of the blocking of the pentose phosphate pathway (PPP) or the activation of the glyoxylate shunt, metabolite profiles were analyzed on M4-Δgnd, M4-ΔiclR and M4 mutants.MethodsMetabolomics was performed by FT-IR and GC–MS for metabolite fingerprinting and HPLC for quantification of succinate and glycerol.ResultsMost of the 65 identified metabolites showed lower relative levels in the M4-ΔiclR and M4-Δgnd mutants than those of the M4. However, fructose 1,6-biphosphate, trehalose, isovaleric acid and mannitol relative concentrations were increased in M4-ΔiclR and M4-Δgnd mutants. To further improve succinate production, the synthesis of mannitol was suppressed by deletion of mannitol dehydrogenase (mtlD) on M4-ΔgndΔmtlD mutant that increase ~ 20% respect to M4-Δgnd.ConclusionMetabolomics can serve as a holistic tool to identify bottlenecks in metabolic pathways by a non-rational design. Genetic manipulation to release these restrictions could increase the production of succinate.

SDH mutations confer complex cross-resistance patterns to SDHIs in Corynespora cassiicola

Succinate dehydrogenase inhibitors (SDHIs) are one of the most frequently used fungicides in cucumber fields in China. Our previous studies indicated that the sensitivity profile of Corynespora cassiicola, the causal agent of Corynespora leaf spot, to different SDHIs varied greatly; however, the underlying mechanism remains unclear. The 50% effective concentration (EC50) values of boscalid, fluopyram, fluxapyroxad and isopyrazam in C. cassiicola collected from 2017 to 2020 shifted, with resistance frequencies of 79.83%, 78.43%, 83.19% and 49.86%, respectively. The sequence alignment of sdhB/C/D of resistant strains revealed that eight single amino acid mutations (B-H278Y/L, B-I280V, C-S73P, C-N75S, C-H134R, D-D95E and D-G109V), and three dual-mutations (B-I280V&C-S73P, B-I280V&C-N75S and C-S73P&C-N75S) conferred various SDHI resistance levels and cross-resistance profiles. The expression level of the sdhB/C/D gene and succinate dehydrogenase (SDH) activity in the mutants were significantly altered by the presence of SDHIs, compared with the wild type strain. Additionally, molecular docking results suggested that the missense mutation influenced the crystal structure of SDH and subsequently interfered with the interaction bonds and bond distances among the target protein and chemicals. In brief, amino acid mutations altered the fungicide response of target gene expression, SDH activity and the binding features of SDH-ligand complexes and subsequently conferred multiple resistance levels and complex cross-resistance patterns to SDHIs in C. cassiicola. The evaluation of C. cassiicola resistance to SDHIs provided a significant foundation for efficient chemical development and integrated CLS management strategies.

Differential HIF2α Protein Expression in Human Carotid Body and Adrenal Medulla under Physiologic and Tumorigenic Conditions.

Simple SummaryThoraco-abdominal paraganglioma and pheochromocytoma (PPGL) are pathogenically linked to mutations in SDH genes. Loss-of-function of SDH has been associated with stabilization of HIF2α, which otherwise would be degraded via oxygen-sensitive mechanisms. SDH dysfunction also predispose to the development of paragangliomas arising at the carotid body or other head and neck paraganglia (HNPGL). Although PPGL and HNPGL share similar features, they have certain clinical and genetic peculiarities. By comparison of HIF2α expression in HNPGL and PPGL, we found that functional HIF2α is overexpressed in 80% of PPGLs, including those with SDH mutations as compared with non-tumor tissue. However, HIF2α is already highly expressed in the carotid body under physiologic conditions, and it is not overexpressed in HNPGL. These data suggest that selective HIF2α inhibitors already in clinical trials may benefit a wide spectrum of PPGL.Hypoxia-inducible factors (HIF) 2α and 1α are the major oxygen-sensing molecules in eukaryotic cells. HIF2α has been pathogenically linked to paraganglioma and pheochromocytoma (PPGL) arising in sympathetic paraganglia or the adrenal medulla (AM), respectively. However, its involvement in the pathogenesis of paraganglioma arising in the carotid body (CB) or other parasympathetic ganglia in the head and neck (HNPGL) remains to be defined. Here, we retrospectively analyzed HIF2α by immunohistochemistry in 62 PPGL/HNPGL and human CB and AM, and comprehensively evaluated the HIF-related transcriptome of 202 published PPGL/HNPGL. We report that HIF2α is barely detected in the AM, but accumulates at high levels in PPGL, mostly (but not exclusively) in those with loss-of-function mutations in VHL and genes encoding components of the succinate dehydrogenase (SDH) complex. This is associated with upregulation of EPAS1 and the HIF2α-regulated genes COX4I2 and ADORA2A. In contrast, HIF2α and HIF2α-regulated genes are highly expressed in CB and HNPGL, irrespective of VHL and SDH dysfunctions. We also found that HIF2α and HIF1α protein expressions are not correlated in PPGL nor HNPGL. In addition, HIF1α-target genes are almost exclusively overexpressed in VHL-mutated HNPGL/PPGL. Collectively, the data suggest that involvement of HIF2α in the physiology and tumor pathology of human paraganglia is organ-of-origin-dependent and HIF1α-independent.

Expanding the clinicopathological spectrum of succinate dehydrogenase-deficient renal cell carcinoma with a focus on variant morphologies: a study of 62 new tumors in 59 patients

AbstractMost succinate dehydrogenase (SDH)-deficient renal cell carcinomas (RCCs) demonstrate stereotypical morphology characterized by bland eosinophilic cells with frequent intracytoplasmic inclusions. However, variant morphologic features have been increasingly recognized. We therefore sought to investigate the incidence and characteristics of SDH-deficient RCC with variant morphologies. We studied a multi-institutional cohort of 62 new SDH-deficient RCCs from 59 patients. The median age at presentation was 39 years (range 19–80), with a slight male predominance (M:F = 1.6:1). A relevant family history was reported in 9 patients (15%). Multifocal or bilateral tumors were identified radiologically in 5 patients (8%). Typical morphology was present at least focally in 59 tumors (95%). Variant morphologies were seen in 13 (21%) and included high-grade nuclear features and various combinations of papillary, solid, and tubular architecture. Necrosis was present in 13 tumors, 7 of which showed variant morphology. All 62 tumors demonstrated loss of SDHB expression by immunohistochemistry. None showed loss of SDHA expression. Germline SDH mutations were reported in all 18 patients for whom the results of testing were known. Among patients for whom follow-up data was available, metastatic disease was reported in 9 cases, 8 of whom had necrosis and/or variant morphology in their primary tumor. Three patients died of disease. In conclusion, variant morphologies and high-grade nuclear features occur in a subset of SDH-deficient RCCs and are associated with more aggressive behavior. We therefore recommend grading all SDH-deficient RCCs and emphasize the need for a low threshold for performing SDHB immunohistochemistry in any difficult to classify renal tumor, particularly if occurring at a younger age.

Genome-wide screening for genes involved in the epigenetic basis of fragile X syndrome.

SummaryFragile X syndrome (FXS), the most prevalent heritable form of intellectual disability, is caused by the transcriptional silencing of the FMR1 gene. The epigenetic factors responsible for FMR1 inactivation are largely unknown. Here, we initially demonstrated the feasibility of FMR1 reactivation by targeting a single epigenetic factor, DNMT1. Next, we established a model system for FMR1 silencing using a construct containing the FXS-related mutation upstream to a reporter gene. This construct was methylated in vitro and introduced into a genome-wide loss-of-function (LOF) library established in haploid human pluripotent stem cells (PSCs), allowing the identification of genes whose functional loss reversed the methylation-induced silencing of the FMR1 reporter. Selected candidate genes were further analyzed in haploid- and FXS-patient-derived PSCs, highlighting the epigenetic and metabolic pathways involved in FMR1 regulation. Our work sheds light on the mechanisms responsible for CGG-expansion-mediated FMR1 inactivation and offers novel targets for therapeutic FMR1 reactivation.

Reversible Regulation of Succinate Dehydrogenase by Tools of Photopharmacology.

Succinate dehydrogenase (SDH) is extremely important in metabolic function and biological processes. Modulation of SDH has been reported to be a promising therapeutic target to SDH mutations. Current measures for the regulation of SDH are scarce, and precise and reversible modulation of SDH still remains challenging. Herein, a powerful tool for reversible optical control of SDH was proposed and evaluated utilizing the technology of photopharmacology. We reported photochromic ligands (PCLs), azobenzene-pyrazole amides (APAs), that exert light-dependent inhibition effects on SDH. Physicochemical property tests and biological assays were conducted to demonstrate the feasibility of modulating SDH. In this paper, common agricultural pathogens were used to develop a procedure by which our PCLs could reversibly and precisely control SDH utilizing green light. This research would help us to understand the target-ligand interactions and provide new insights into modulation of SDH.

Asymptomatic carriers of mutations in succinate dehydrogenase (SDHx) genes. In search of consensus for follow-up

Asymptomatic carriers of mutations in succinate dehydrogenase (SDHx) genes. In search of consensus for follow-up

SDHB knockout and succinate accumulation are insufficient for tumorigenesis but dual SDHB/NF1 loss yields SDHx-like pheochromocytomas.

SUMMARYInherited pathogenic succinate dehydrogenase (SDHx) gene mutations cause the hereditary pheochromocytoma and paraganglioma tumor syndrome. Syndromic tumors exhibit elevated succinate, an oncometabolite that is proposed to drive tumorigenesis via DNA and histone hypermethylation, mitochondrial expansion, and pseudohypoxia-related gene expression. To interrogate this prevailing model, we disrupt mouse adrenal medulla SDHB expression, which recapitulates several key molecular features of human SDHx tumors, including succinate accumulation but not 5hmC loss, HIF accumulation, or tumorigenesis. By contrast, concomitant SDHB and the neurofibromin 1 tumor suppressor disruption yields SDHx-like pheochromocytomas. Unexpectedly, in vivo depletion of the 2-oxoglutarate (2-OG) dioxygenase cofactor ascorbate reduces SDHB-deficient cell survival, indicating that SDHx loss may be better tolerated by tissues with high antioxidant capacity. Contrary to the prevailing oncometabolite model, succinate accumulation and 2-OG-dependent dioxygenase inhibition are insufficient for mouse pheochromocytoma tumorigenesis, which requires additional growth-regulatory pathway activation.

Head/neck paragangliomas: focus on tumor location, mutational status and plasma methoxytyramine.

Head and neck paragangliomas (HNPGLs) are tumors of parasympathetic origin that occur at variable locations and are often secondary to germline mutations in succinate dehydrogenase (SDH) subunit genes. Occasionally, these tumors produce catecholamines. Here, we assessed whether different locations of HNPGLs relate to the presence of SDHx mutations, catecholamine production and other presentations. In this multicenter study, we collected clinical and biochemical data from 244 patients with HNPGLs and 71 patients without HNPGLs. We clarified that jugulotympanic HNPGLs have distinct features. In particular, 88% of jugulotympanic HNPGLs arose in women, among whom only 24% occurred due to SDHx mutations compared to 55% in men. Jugulotympanic HNPGLs were also rarely bilateral, were of a smaller size and were less often metastatic compared to carotid body and vagal HNPGLs. Furthermore, we showed that plasma concentrations of methoxytyramine (MTY) were higher (P < 0.0001) in patients with HNPGL than without HNPGL, whereas plasma normetanephrine did not differ. Only 3.7% of patients showed strong increases in plasma normetanephrine. Plasma MTY was positively related to tumor size but did not relate to the presence of SDHx mutations or tumor location. Our findings confirm that increases in plasma MTY represent the main catecholamine-related biochemical feature of patients with HNPGLs. We expect that more sensitive analytical methods will make biochemical testing of HNPGLs more practical in the future and enable more than the current 30% of patients to be identified with dopamine-producing HNPGLs. The sex-dependent differences in the development of HNPGLs may have relevance to the diagnosis, management and outcomes of these tumors.

Double Mutations in Succinate Dehydrogenase Are Involved in SDHI Resistance in Corynespora cassiicola.

Simple SummaryWith the application of fungicide in agriculture, resistance to fungicide has become a serious problem. It is important to assess the evolution of resistance for development of disease prevention and control. We confirmed, by site-directed mutagenesis, that single mutations conferring moderate or low resistance are more likely to evolve into double mutations conferring higher resistance under the selective pressure of SDHI. However, the double mutations suffer large of fitness penalty than single mutation. We recommend that the use of SDHI in agriculture should be appropriately reduced or that other types of fungicides should be used to control plant diseases, such as dicarboximide fungicides (DCFs), to avoid the emergence of very resistant plant pathogens.With the further application of succinate dehydrogenase inhibitors (SDHI), the resistance caused by double mutations in target gene is gradually becoming a serious problem, leading to a decrease of control efficacy. It is important to assess the sensitivity and fitness of double mutations to SDHI in Corynespora cassiicola and analysis the evolution of double mutations. We confirmed, by site-directed mutagenesis, that all double mutations (B-I280V+D-D95E/D-G109V/D-H105R, B-H278R+D-D95E/D-G109V, B-H278Y+D-D95E/D-G109V) conferred resistance to all SDHI and exhibited the increased resistance to at least one fungicide than single point mutation. Analyses of fitness showed that all double mutations had lower fitness than the wild type; most of double mutations suffered more fitness penalties than the corresponding single mutants. We also further found that double mutations (B-I280V+D-D95E/D-G109V/D-H105R) containing low SDHI-resistant single point mutation (B-I280V) exhibited higher resistance to SDHI and low fitness penalty than double mutations (B-H278Y+D-D95E/D-G109V) containing high SDHI-resistant single mutations (B-H278Y). Therefore, we may infer that a single mutation conferring low resistance is more likely to evolve into a double mutation conferring higher resistance under the selective pressure of SDHI. Taken together, our results provide some important reference for resistance management.

Functional succinate dehydrogenase deficiency is a common adverse feature of clear cell renal cancer

Significance This study demonstrates that underexpression of succinate dehydrogenase (SDH) subunits resulting in accumulation of oncogenic succinate is a common, adverse, epigenetic modulating feature in clear cell renal cell carcinoma (ccRCC), during pathogenesis and progression. The study sheds light on the mechanisms of down-regulation of SDH subunits in ccRCC and deciphers the consequent oncogenic effects. It shows that functional SDH deficiency is a common feature of ccRCC (∼80% of all kidney cancers), and not just limited to the 0.05 to 0.5% of kidney cancers with germline SDH mutations.

Familial SDHB gene mutation in disseminated non-hypoxia-related malignant paraganglioma treated with [90Y]Y/[177Lu]Lu- DOTATATE.

Familial paraganglioma may be related to mutations in succinate dehydrogenase (SDH) enzyme complex genes. Among patients with hereditary paraganglioma, SDH subunit B (SDHB) gene mutations are associated with the highest morbidity and mortality related to a higher malignancy rate. We report a family with the c.689G>A (p.Arg230His) mutation in the SDHB gene identified in two family members, a father and his daughter. While the 14-year-old daughter had no evidence of clinical disease, recurrent and later disseminated [131I]metaiodobenzylguanidine uptake-negative head and neck paraganglioma with multiple bone metastases developed in the father who underwent peptide receptor radionuclide therapy with [90Y]Y/[177Lu]Lu-dodecane tetraacetic acid octreotate (DOTATATE) at the time of the genetic diagnosis. This treatment was repeated 6 years later due to disease progression and the patient, who is currently 49 years old, remains alive and in good overall clinical condition at 8 years of follow-up after the original presentation at our unit. The growing armamentarium of imaging methods available for such patients may inform decision making regarding choice of the optimal treatment approach, potentially contributing to improved outcomes.

Diagnostic Role of Diffusion-Weighted and Dynamic Contrast-Enhanced Perfusion MR Imaging in Paragangliomas and Schwannomas in the Head and Neck.

Distinguishing schwannomas from paragangliomas in the head and neck and determining succinate dehydrogenase (SDH) mutation status in paragangliomas are clinically important. We aimed to assess the clinical usefulness of DWI and dynamic contrast-enhanced MR imaging in differentiating these 2 types of tumors, as well as the SDH mutation status of paragangliomas. This retrospective study from June 2016 to June 2020 included 42 patients with 15 schwannomas and 27 paragangliomas (10 SDH mutation-positive and 17 SDH mutation-negative). ADC values, dynamic contrast-enhanced MRI parameters, and tumor imaging characteristics were compared between the 2 tumors and between the mutation statuses of paragangliomas as appropriate. Multivariate stepwise logistic regression analysis was performed to identify significant differences in these parameters. Fractional plasma volume (P ≤ .001), rate transfer constant (P = .038), time-to-maximum enhancement (P < .001), maximum signal-enhancement ratio (P < .001) and maximum concentration of contrast agent (P < .001), velocity of enhancement (P = .002), and tumor characteristics including the presence of flow voids (P = .001) and enhancement patterns (P = .027) showed significant differences between schwannomas and paragangliomas, though there was no significant difference in ADC values. In the multivariate logistic regression analysis, fractional plasma volume was identified as the most significant value for differentiation of the 2 tumor types (P = .014). ADC values were significantly higher in nonhereditary than in hereditary paragangliomas, while there was no difference in dynamic contrast-enhanced MR imaging parameters. Dynamic contrast-enhanced MR imaging parameters show promise in differentiating head and neck schwannomas and paragangliomas, while DWI can be useful in detecting SDH mutation status in paragangliomas.

Succinate Dehydrogenase Mutation and Paraganglioma Syndromes: A Review Article

Succinate Dehydrogenase Mutation and Paraganglioma Syndromes: A Review Article

Peptide receptor radionuclide therapy in patients with metastatic progressive pheochromocytoma and paraganglioma: long-term toxicity, efficacy and prognostic biomarker data of phase II clinical trials

BackgroundPheochromocytoma and paraganglioma (PPGL) have currently only limited treatment options available for patients in the metastatic phase (mPPGL) in either post-surgery or inoperable settings. However, these rare tumors overexpress somatostatin receptors and can thus be treated with peptide receptor radionuclide therapy (PRRT). We present data about our 10-year experience treating 46 consecutive mPPGL patients with 90Y-DOTATOC or 177Lu-DOTATATE.Patients and methodsAll patients (20 men and 26 women, median age 52 years) showed positive scintigraphic imaging at 111In-octreotide or 68Ga-DOTATOC positron emission tomography/computed tomography (PET/CT). 90Y-DOTATOC was administered in 12 patients, with cumulative dosages ranging from 7.4 to 11 GBq, while 34 patients received 18.5 or 27.5GBq of 177Lu-DOTATATE. We used Southwest Oncology Group Response Evaluation Criteria in Solid Tumors criteria to evaluate treatment efficacy and Common Terminology Criteria for Adverse Events criteria to assess toxicity. The prognostic role of primary tumor site, hormone secretion, succinate dehydrogenase (SDHx) mutation, and metastatic involvement was also evaluated.ResultsBoth 90Y-DOTATOC and 177Lu-DOTATATE PRRT were well tolerated by patients without significant renal or bone marrow toxicity. The median follow-up was 73 months (range 5-146 months). The overall disease control rate (DCR) was 80% [95% confidence interval (CI) 68.9% to 91.9%] with a mean five cycles of therapy. However, 177Lu-DOTATATE patients showed a longer median overall survival (mOS) than those receiving 90Y-Dotatoc and a better DCR when higher dosages were administered, even if a direct comparison was not carried out. Syndromic patients had a poorer mOS. SDHx mutations did not interfere with treatment efficacy.ConclusionsPRRT is safe and effective for the treatment of patients with progressive mPPGL, especially at higher dosages. The longer mOS of 177Lu-DOTATATE-treated patients in our protocols indicates the former radiopharmaceutical as the better candidate for further clinical application.

Assessment of MR Imaging and CT in Differentiating Hereditary and Nonhereditary Paragangliomas.

Head and neck paragangliomas have been reported to be associated with mutations of the succinate dehydrogenase enzyme family. The aim of this study was to assess whether radiologic features could differentiate between paragangliomas in the head and neck positive and negative for the succinate dehydrogenase mutation. This single-center retrospective review from January 2015 to January 2020 included 40 patients with 48 paragangliomas (30 tumors positive for succinate dehydrogenase mutation in 23 patients and 18 tumors negative for the succinate dehydrogenase mutation in 17 patients). ADC values and tumor characteristics on CT and MR imaging were evaluated by 2 radiologists. Differences between the 2 cohorts in the diagnostic performance of ADC and normalized ADC (ratio to ADC in the medulla oblongata) values were evaluated using the independent samples t test. P < .05 was considered significant. ADCmean (1.07 [SD, 0.25]/1.04 [SD, 0.12] versus 1.31 [SD, 0.16]/1.30 [SD, 0.20]× 10-3 mm2/s by radiologists 1 and 2; P < .001), ADCmaximum (1.49 [SD, 0.27]/1.49 [SD, 0.20] versus 2.01 [SD, 0.16]/1.87 [SD, 0.20] × 10-3 mm2/s; P < .001), normalized ADCmean (1.40 [SD, 0.33]/1.37 [SD, 0.16] versus 1.73 [SD, 0.22]/1.74 [SD, 0.27]; P < .001), and normalized ADCmaximum (1.95 [SD, 0.37]/1.97 [SD, 0.27] versus 2.64 [SD, 0.22]/2.48 [SD, 0.28]; P < .001) were significantly lower in succinate dehydrogenase mutation-positive than mutation-negative tumors. ADCminimum, normalized ADCminimum, and tumor characteristics were not statistically significant. ADC is a promising imaging biomarker that can help differentiate succinate dehydrogenase mutation-positive from mutation-negative paragangliomas in the head and neck.

Extracellular Vesicles From SDHB Deficient hPheo1 Cells Activate STAT3 in Wild-Type Cells

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors that originate from the adrenal medulla and extra-adrenal paraganglia, respectively. Inactivating mutations in succinate dehydrogenase (SDHx) genes leads to succinate accumulation, increased HIF1-α levels, and uncontrollable growth of PPGLs. We hypothesized that small extracellular vesicles (EVs) released from progenitor cells derived from pheochromocytoma (hPheo1) with a shRNA mediated knockdown of SDHB are enriched in succinate metabolites that play a key role in the activation of various tyrosine dependent signaling pathways that are involved in turmorigenesis and proliferation. We isolated EVs from the conditioned media of human wild-type hPheo1 cells and hPheo1 cells with shRNA SDHB knockdown. The EVs from three separate preparations of each group were characterized by nanoparticle tracking analysis, transmission electron microscopy, and Western blotting using antibodies against different types of EV and one non-EV marker. Our results show small EVs from the SDHB knockdown hPheo1 cells increased the activation of phosphotyrosine residues in wild-type cells compared to cells treated with control EVs from the same cell type. Additionally, our data show these EVs increase phospho-STAT3 compared to the control EVs (3843.10 +/- 1138.89 vs. 213.65+/- 40.75; p<0.05; n=3) in cultured wild-type hPheo1 cells. Protein tyrosine kinases (PTKs) control various cellular processes including growth, differentiation, and metabolism by activating various signaling pathways including STAT3. The significance of these findings is that in some cancers, elevated succinate from a SDHx mutation has been shown to activate STAT3 which may explain a possible pathway for tumorigenesis. Studies from other investigators have shown that STAT3 expression is elevated in malignant PPGL tissues. Through enriched EV analysis our findings have confirmed the role of STAT3 in SDHB deficient cells. Additional studies are needed to identify other metabolites that are enriched in EVs that regulate phosphorylation of tyrosine residues and STAT3 activation.

Malonate Promotes Adult Cardiomyocyte Proliferation and Heart Regeneration

Neonatal mouse cardiomyocytes undergo a metabolic switch from glycolysis to oxidative phosphorylation, which results in a significant increase in reactive oxygen species production that induces DNA damage. These cellular changes contribute to cardiomyocyte cell cycle exit and loss of the capacity for cardiac regeneration. The mechanisms that regulate this metabolic switch and the increase in reactive oxygen species production have been relatively unexplored. Current evidence suggests that elevated reactive oxygen species production in ischemic tissues occurs as a result of accumulation of the mitochondrial metabolite succinate during ischemia via succinate dehydrogenase (SDH), and this succinate is rapidly oxidized at reperfusion. Mutations in SDH in familial cancer syndromes have been demonstrated to promote a metabolic shift into glycolytic metabolism, suggesting a potential role for SDH in regulating cellular metabolism. Whether succinate and SDH regulate cardiomyocyte cell cycle activity and the cardiac metabolic state remains unclear. Here, we investigated the role of succinate and SDH inhibition in regulation of postnatal cardiomyocyte cell cycle activity and heart regeneration. Our results demonstrate that injection of succinate into neonatal mice results in inhibition of cardiomyocyte proliferation and regeneration. Our evidence also shows that inhibition of SDH by malonate treatment after birth extends the window of cardiomyocyte proliferation and regeneration in juvenile mice. Remarkably, extending malonate treatment to the adult mouse heart after myocardial infarction injury results in a robust regenerative response within 4 weeks after injury via promoting adult cardiomyocyte proliferation and revascularization. Our metabolite analysis after SDH inhibition by malonate induces dynamic changes in adult cardiac metabolism. Inhibition of SDH by malonate promotes adult cardiomyocyte proliferation, revascularization, and heart regeneration via metabolic reprogramming. These findings support a potentially important new therapeutic approach for human heart failure.

Improving Outcomes in Carotid Body Tumors Treatment: The Impact of a Multidisciplinary Team Approach

The purpose of this study was to evaluate how a multidisciplinary approach, including patients and familiar genetic counseling, preoperative succinate-dehydrogenase (SDH) gene mutation analysis, preoperative adjunctive endovascular procedures (PAEPs) and postoperative rehabilitative team may affect the outcomes in patients who underwent surgery for carotid body tumors (CBTs). Fifty-seven consecutive CBT resections were performed from January 1995 to December 2019 in a single center institution. Two groups of patients were compared: group A (1995-2003; n = 10) and group B (2004-2019; n = 47), treated before and after the establishment of a multidisciplinary approach to CBTs. Group A and group B were evaluated retrospectively and prospectively for SDH mutations, respectively. PAEPs (external carotid artery stenting, percutaneous transfemoral embolization or direct percutaneous puncture of the tumor with simultaneous embolization) were performed only in patients of group B, when the size of the tumor exceeded the 45 mm. Primary endpoints were blood loss (BL) and cranial nerve injuries. Secondary endpoint was the number of new silent masses (NSMs) discovered after genetic evaluation. SDH mutations were found in 2 patients of group A and in 11 patients of group B. There were no significant differences in mass diameter between the groups. A significant difference regarding the surgical procedure time was observed in the 2 groups, with a higher time in the group A (Group A: 180 ± 77.3; Group B: 138 ± 54.5, P= 0.04). BL was significantly lower in group B (203 ± 69.5 mL vs. 356 ± 102 mL; P = 0.0001), as well as for patients underwent PAEPs vs. those underwent direct surgery (n = 15, 149 ± 53 mL vs. n = 42, 273 ± 88 mL; P = 0.0001). No differences between transient and persistent cranial nerve injuries were observed between the 2 groups. Carotid reconstruction was necessary for 2 patients of group A (n = 2 vs. n = 0; P = 0.02). Unilateral tumor recurrence was detected in 7 patients, with a significantly higher rate (P ≤ 0.002) in patients carrying SDH mutations compared to those without SDH mutation (wild-type). SDH mutations detected in the groups lead to discover 7 NSMs (group A n = 1 vs. group B n = 6; P = 1.00). The impact of the multidisciplinary team suggests that surgical resection still remains the gold standard for the treatment of CBTs, but the use of PAEPs in selected cases may reduce surgical procedure time, BL and the need for reconstructive carotid surgery. Genetic counseling and SDH gene analysis allow to diagnose NSMs in asymptomatic patients. Larger studies should be considered to evaluate the effectiveness of postoperative rehabilitative program.

Unexpected obesity, rather than tumorigenesis, in a conditional mouse model of mitochondrial complex II deficiency.

Mutations in any of the genes encoding the four subunits of succinate dehydrogenase (SDH), a mitochondrial membrane‐bound enzyme complex that is involved in both the tricarboxylic acid cycle and the electron transport chain, can lead to a variety of disorders. Recognized conditions with such mutations include Leigh syndrome and hereditary tumors such as pheochromocytoma and paraganglioma (PPGL), renal cell carcinoma, and gastrointestinal stromal tumor. Tumors appear in SDH mutation carriers with dominant inheritance due to loss of heterozygosity in susceptible cells. Here, we describe a mouse model intended to reproduce hereditary PPGL through Cre‐mediated loss of SDHC in cells that express tyrosine hydroxylase (TH), a compartment where PPGL is known to originate. We report that while there is modest expansion of TH+ glomus cells in the carotid body upon SDHC loss, PPGL is not observed in such mice, even in the presence of a conditional dominant negative p53 protein and chronic hypoxia. Instead, we report an unexpected phenotype of nondiabetic obesity beginning at about 20 weeks of age. We hypothesize that this obesity is caused by TH+ cell loss or altered phenotype in key compartments of the central nervous system responsible for regulating feeding behavior, coupled with metabolic changes due to loss of peripheral catecholamine production.