Pericardium decellularization in a one-day, two-step protocol.

Scaffolds used in tissue engineering can be obtained from synthetic or natural materials, always focusing the effort on mimicking the extracellular matrix of human native tissue. In this study, a decellularization process is used to obtain an acellular, biocompatible non-cytotoxic human pericardium graft as a bio-substitute. An enzymatic and hypertonic method was used to decellularize the pericardium. Histological analyses were performed to determine the absence of cells and ensure the integrity of the extracellular matrix (ECM). In order to measure the effect of the decellularization process on the tissue's biological and mechanical properties, residual genetic content and ECM biomolecules (collagen, elastin, and glycosaminoglycan) were quantified and the tissue's tensile strength was tested. Preservation of the biomolecules, a residual genetic content below 50 ng/mg dry tissue, and maintenance of the histological structure provided evidence for the efficacy of the decellularization process, while preserving the ECM. Moreover, the acellular tissue retains its mechanical properties, as shown by the biomechanical tests. Our group has shown that the acellular pericardial matrix obtained through the super-fast decellularization protocol developed recently retains the desired biomechanical and structural properties, suggesting that it is suitable for a broad range of clinical indications.

Last twenty-years activity of cardiovascular tissue banking in Barcelona.

The Barcelona Tissue Bank was established from the merge of two previous multi-tissue banks. Potential donors are screened by Donor Center staff and multi-tissue retrieval is performed by specialized own teams. Tissue processing and preservation is performed in clean room facilities by specialised personnel. After quality control of both donor and all tissues results, the heart valves and vascular segments are stored until medical request. The aim of this report is to present the cardiovascular tissue activity and retrospectively evaluate the outcomes of the changes performed in last 20 years. Cardiovascular tissue from 4088 donors was received, specifically 3115 hearts and 2095 vascular segments were processed and evaluated. A total of 48% of the aortic valves, 68% of the pulmonary valves and 75% of the vascular segments were suitable for transplant. The main reason for discarding tissue was macroscopic morphology followed by microbiological results, for both valves and arteries. Altogether, 4360 tissues were distributed for transplantation: 2032 (47%) vascular segments, 1545 (35%) pulmonary valves and 781 (18%) aortic valves. The most common indication for aortic valve surgery was the treatment of endocarditis, while for pulmonary valves, it was congenital malformation reconstruction. Vascular segments were mainly used for reconstruction after ischemia. During this period, a number of changes were made with the goal of enhancing tissue quality, safety and efficacy. These improvements were achieved through the use of a new antibiotic cocktail, increasing of donor age criteria and changing the microbiological control strategy.

Effect of surgical treatment on myocardial strain in patients with pheochromocytoma and paraganglioma: a mini-review and meta-analysis.

AIM: Information on systolic dysfunction, as assessed by left-ventricular (LV) mechanics, in patients with pheochromocytoma after surgical treatment is scanty. We performed a systematic meta-analysis of speckle tracking echocardiographic studies to provide an updated comprehensive information on this issue. METHODS: The PubMed, OVID-MEDLINE, and Cochrane library databases were analyzed to search for articles published from the inception up to May 31st 2021. Studies were identified using MeSH terms and crossing the following search items: "myocardial strain" "left ventricular mechanics", "speckle tracking echocardiography", "systolic dysfunction", "pheochromocytoma", and "paraganglioma". RESULTS: A total of 92 surgically treated patients with pheochromocytoma/paraganglioma were included in 3 longitudinal studies. Successful surgical treatment was associated with a decrease in relative wall thickness (SMD - 0.25 ± 0.10, CI - 0.45/- 0.05, p < 0.01) and an improvement in global longitudinal strain (SMD - 0.45 ± 0.10, CI - 0.66/- 0.24, p < 0.0001). The favorable effects of treatment on LV geometry and mechanics were not accompanied by significant changes in ejection fraction (SMD - 0.07 ± 0.10, CI - 0.27/0.12, p = 0.44). CONCLUSIONS: This meta-analysis adds a new piece of evidence, suggesting that surgical treatment of patients with pheochromocytoma impacts favorably on LV geometry and LV mechanics, and, more importantly, the assessment of LV changes in this setting can no longer rely on conventional echocardiographic parameters such as ejection fraction.

Advanced Quantification Methods To Improve the 18b Dormancy Model for Assessing the Activity of Tuberculosis Drugs In Vitro.

One of the reasons for the lengthy tuberculosis (TB) treatment is the difficulty to treat the nonmultiplying mycobacterial subpopulation. In order to assess the ability of (new) TB drugs to target this subpopulation, we need to incorporate dormancy models in our preclinical drug development pipeline. In most available dormancy models, it takes a long time to create a dormant state, and it is difficult to identify and quantify this nonmultiplying condition. The Mycobacterium tuberculosis 18b strain might overcome some of these problems, because it is dependent on streptomycin for growth and becomes nonmultiplying after 10 days of streptomycin starvation but still can be cultured on streptomycin-supplemented culture plates. We developed our 18b dormancy time-kill kinetics model to assess the difference in the activity of isoniazid, rifampin, moxifloxacin, and bedaquiline against log-phase growth compared to the nonmultiplying M. tuberculosis subpopulation by CFU counting, including a novel area under the curve (AUC)-based approach as well as time-to-positivity (TTP) measurements. We observed that isoniazid and moxifloxacin were relatively more potent against replicating bacteria, while rifampin and high-dose bedaquiline were equally effective against both subpopulations. Moreover, the TTP data suggest that including a liquid culture-based method could be of additional value, as it identifies a specific mycobacterial subpopulation that is nonculturable on solid media. In conclusion, the results of our study underline that the time-kill kinetics 18b dormancy model in its current form is a useful tool to assess TB drug potency and thus has its place in the TB drug development pipeline.

Unraveling Polymeric Nanoparticles Cell Uptake Pathways: Two Decades Working to Understand Nanoparticles Journey to Improve Gene Therapy.

Polymeric nanoparticles have aroused an increasing interest in the last decades as novel advanced delivery systems to improve the treatment of many diseases. Hard work has been performed worldwide designing and developing polymeric nanoparticles using different building blocks, which target specific cell types, trying to avoid bioaccumulation and degradation pathways. The main handicap of the design is to understand the final fate and the journey that the nanoparticle will follow, which is intimately ligated with the chemical and physical properties of the nanoparticles themselves and specific factors of the targeted cells. Although the huge number of published scientific articles regarding polymeric nanoparticles for biomedical applications, their use in clinics is still limited. This fact could be explained by the limited data reporting the interaction of the huge diversity of polymeric nanoparticles with cells. This knowledge is essential to understand nanoparticle uptake and trafficking inside cells to the subcellular target structure.In this chapter, we aim to contribute to this field of knowledge by: (1) summarizing the polymeric nanoparticles properties and cellular factors that influence nanoparticle endocytosis and (2) reviewing the endocytic pathways classified as a function of nanoparticle size and as a function of the receptor playing a role. The revision of previously reported endocytic pathways for particular polymeric nanoparticles could facilitate scientist involved in this field to easily delineate efficient delivery systems based on polymeric nanoparticles.

High-resolution array-CGH analysis on 46,XX patients affected by early onset primary ovarian insufficiency discloses new genes involved in ovarian function.

STUDY QUESTION: Can high resolution array-CGH analysis on a cohort of women showing a primary ovarian insufficiency (POI) phenotype in young age identify copy number variants (CNVs) with a deleterious effect on ovarian function? SUMMARY ANSWER: This approach has proved effective to clarify the role of CNVs in POI pathogenesis and to better unveil both novel candidate genes and pathogenic mechanisms. WHAT IS KNOWN ALREADY: POI describes the progression toward the cessation of ovarian function before the age of 40 years. Genetic causes are highly heterogeneous and despite several genes being associated with ovarian failure, most of genetic basis of POI still needs to be elucidated. STUDY DESIGN, SIZE, DURATION: The current study included 67 46,XX patients with early onset POI (<19 years) and 134 control females recruited between 2012 and 2016 at the Medical Cytogenetics and Molecular Genetics Lab, IRCCS Istituto Auxologico Italiano. PARTICIPANTS/MATERIALS, SETTING, METHODS: High resolution array-CGH analysis was carried out on POI patients' DNA. Results of patients and female controls were analyzed to search for rare CNVs. All variants were validated and subjected to a gene content analysis and disease gene prioritization based on the present literature to find out new ovary candidate genes. Case-control study with statistical analysis was carried out to validate our approach and evaluate any ovary CNVs/gene enrichment. Characterization of particular CNVs with molecular and functional studies was performed to assess their pathogenic involvement in POI. MAIN RESULTS AND THE ROLE OF CHANCE: We identified 37 ovary-related CNVs involving 44 genes with a role in ovary in 32 patients. All except one of the selected CNVs were not observed in the control group. Possible involvement of the CNVs in POI pathogenesis was further corroborated by a case-control analysis that showed a significant enrichment of ovary-related CNVs/genes in patients (P = 0.0132; P = 0.0126). Disease gene prioritization identified both previously reported POI genes (e.g. BMP15, DIAPH2, CPEB1, BNC1) and new candidates supported by transcript and functional studies, such as TP63 with a role in oocyte genomic integrity and VLDLR which is involved in steroidogenesis. LARGE SCALE DATA: ClinVar database (http://www.ncbi.nlm.nih.gov/clinvar/); accession numbers SCV000787656 to SCV000787743. LIMITATIONS, REASONS FOR CAUTION: This is a descriptive analysis for almost all of the CNVs identified. Inheritance studies of CNVs in some non-familial sporadic cases was not performed as the parents' DNA samples were not available. Addionally, RT-qPCR analyses were carried out in few cases as RNA samples were not always available and the genes were not expressed in blood. WIDER IMPLICATIONS OF THE FINDINGS: Our array-CGH screening turned out to be efficient in identifying different CNVs possibly implicated in disease onset, thus supporting the extremely wide genetic heterogeneity of POI. Since almost 50% of cases are negative rare ovary-related CNVs, array-CGH together with next generation sequencing might represent the most suitable approach to obtain a comprehensive genetic characterization of POI patients. STUDY FUNDING/COMPETING INTEREST(S): Supported by Italian Ministry of Health grants 'Ricerca Corrente' (08C203_2012) and 'Ricerca Finalizzata' (GR-2011-02351636, BIOEFFECT) to IRCCS Istituto Auxologico Italiano.

Adipocyte proteome and secretome influence inflammatory and hormone pathways in glioma.

Gliomas represent the most common primary malignant brain tumors in adults, with an extremely poor prognosis. Among several risk factors, lifestyle was also recently identified as a major risk factor for the development of primary glioma. In the present study, we explore the relationship between obesity and glioma in a cellular model. Thus, we have study the influence of adipocytes secretome on glioma cell line GL261. Using the 3T3-L1 adipocyte cell line, and its conditioned medium (adipokines-enriched medium), we showed that adipocyte-released factors relate with glioma angiogenic, growth, hormones and metabolic behavior by MALDI-TOF-MS and proteomic array analysis. In a first view, STI1, hnRNPs and PGK1 are under expressed on CGl. Similarly, both carbonic anhydrase and aldose reductase are even suppressed in glioma cells that grown under adipokines-enriched environment. Contrariwise, RFC1, KIF5C, ANXA2, N-RAP and RACK1 are overexpressed in GL261 cell the in the presence of the adipokines-enriched medium. We further identified the factors that are released by adipocyte cells, and revealed that several pro-inflammatory and angiogenic factors, such as IL-6, IL-11, LIF, PAI-1, TNF-α, endocan, HGF, VEGF IGF-I, were secreted to the medium into a high extent, whereas TIMP-1 and SerpinE1 were under expressed on CGl. This study discloses an interesting in vitro model for the study of glioma biology under a "obesity" environment, that can be explored for the understanding of cancer cells biology, for the search of biomarkers, prognostic markers and therapeutic approaches.

Pharmacological enhancement of mGlu5 receptors rescues behavioral deficits in SHANK3 knock-out mice.

SHANK3 (also called PROSAP2) genetic haploinsufficiency is thought to be the major cause of neuropsychiatric symptoms in Phelan-McDermid syndrome (PMS). PMS is a rare genetic disorder that causes a severe form of intellectual disability (ID), expressive language delays and other autistic features. Furthermore, a significant number of SHANK3 mutations have been identified in patients with autism spectrum disorders (ASD), and SHANK3 truncating mutations are associated with moderate to profound ID. The Shank3 protein is a scaffold protein that is located in the postsynaptic density (PSD) of excitatory synapses and is crucial for synapse development and plasticity. In this study, we investigated the molecular mechanisms associated with the ASD-like behaviors observed in Shank3Δ11-/- mice, in which exon 11 has been deleted. Our results indicate that Shank3 is essential to mediating metabotropic glutamate receptor 5 (mGlu5)-receptor signaling by recruiting Homer1b/c to the PSD, specifically in the striatum and cortex. Moreover, augmenting mGlu5-receptor activity by administering 3-Cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide ameliorated the functional and behavioral defects that were observed in Shank3Δ11-/- mice, suggesting that pharmaceutical treatments that increase mGlu5 activity may represent a new approach for treating patients that are affected by PMS and SHANK3 mutations.

Estimation of the frequency of Q fever in sheep, goat and cattle herds in France: results of a 3-year study of the seroprevalence of Q fever and excretion level of Coxiella burnetii in abortive episodes.

A study was carried out, from 2012 to 2015, in 10 French départements to estimate the serological prevalence of Q fever and the frequency of abortive episodes potentially related to Coxiella burnetii in a large sample of cattle, sheep and goat herds. The serological survey covered 731 cattle, 522 sheep and 349 goat herds, randomly sampled. The frequency of abortive episodes potentially related to C. burnetii was estimated by investigating series of abortions in 2695 cattle, 658 sheep and 105 goat herds using quantitative polymerase chain reaction analyses and complementary serological results when needed. The average between-herd seroprevalence was significantly lower for cattle (36·0%) than for sheep (55·7%) and goats (61·0%) and significantly higher for dairy herds (64·9% for cattle and 75·6% for sheep) than for meat herds (18·9% for cattle and 39·8% for sheep). Within-herd seroprevalence was also significantly higher for goats (41·5%) than for cattle (22·2%) and sheep (25·7%). During the study period, we estimated that 2·7% (n = 90), 6·2% (n = 48) and 16·7% (n = 19) of the abortive episodes investigated could be 'potentially related to C. burnetii'in cattle, sheep and goat herds, respectively. Overall, strong variability was observed between départements and species, suggesting that risk factors such as herd density and farming practices play a role in disease transmission and maintenance.

Epidemiology and molecular characterization of adult genetic myopathies in a southeastern region of Spain. / Epidemiología y caracterización molecular de las miopatías genéticas en adultos en una región del sureste de España.

INTRODUCTION: Genetic myopathies constitute a collection of rare diseases that significantly impact patient functionality and quality of life. Early diagnosis of genetic myopathies can prevent future complications and provide families with genetic counselling. Despite the substantial impact of genetic myopathies on the adult population, the global epidemiology of these disorders is inadequately addressed in the literature. AIMS: To enhance understanding of both the epidemiology and genetics of these disorders within the province of Alicante, situated in southeastern Spain. MATERIAL AND METHODS: Between 2020 and 2022, a prospective observational study was conducted at the Alicante Health Area-General Hospital, enrolling patients aged 16 years or older with suspected genetic myopathies. Sociodemographic, clinical, and genetic data were collected. The reference date for prevalence calculation was established as December 31, 2022. Official demographic data of the health area were used to set the population at risk. RESULTS: In total, 83 patients were identified with confirmed genetically related myopathy, resulting in an overall prevalence of 29.59 cases per 100,000 inhabitants. The diagnostic yield for molecular genetic testing was found to be 69.16%. The most prevalent genetic myopathies identified included myotonic dystrophy (27.5%), dystrophinopathies (15.7%), and facioscapulohumeral dystrophy (15.7%). CONCLUSION: The prevalence of GMs can vary considerably depending on the geographical region and the studied population. The analysis of diagnostic yield suggests that genetic studies should be considered useful in the diagnosis of genetic myopathies.

TITLE: Epidemiología y caracterización molecular de las miopatías genéticas en adultos en una región del sureste de España.Introducción. Las miopatías genéticas constituyen un conjunto de enfermedades raras que impactan significativamente en la funcionalidad y la calidad de vida del paciente. Un diagnóstico temprano de las miopatías genéticas puede prevenir complicaciones futuras y proporcionar a las familias asesoramiento genético. A pesar del impacto sustancial de las miopatías genéticas en población adulta, la epidemiología global de estos trastornos está inadecuadamente abordada en la bibliografía. Objetivos. Mejorar el entendimiento tanto de la epidemiología como de la genética de estos trastornos en la provincia de Alicante, situada en el sureste de España. Material y métodos. Entre 2020 y 2022, se llevó a cabo un estudio observacional prospectivo en el área de salud Alicante-Hospital General, que incluyó a pacientes de 16 años o más con sospecha de miopatías genéticas. Se recopilaron datos sociodemográficos, clínicos y genéticos. La fecha de referencia para el cálculo de la prevalencia se estableció el 31 de diciembre de 2022. Se utilizaron datos demográficos oficiales del área de salud para establecer la población en riesgo. Resultados. En total, se identificó a 83 pacientes con miopatía genéticamente confirmada, lo que dio lugar a una prevalencia total de 29,59 casos por cada 100.000 habitantes. El rendimiento diagnóstico de las pruebas genéticas moleculares fue del 69,16%. Las miopatías genéticas más frecuentes incluyeron la distrofia miotónica (27,5%), las distrofinopatías (15,7%) y la distrofia facioescapulohumeral (15,7%). Conclusión. La prevalencia de las miopatías genéticas puede variar considerablemente dependiendo de la región geográfica y la población estudiada. El análisis del rendimiento diagnóstico sugiere que los estudios genéticos deberían considerarse útiles en el diagnóstico de las miopatías genéticas.

Development of a full-thickness acellular dermal graft from human skin: Case report of first patient rotator cuff patch augmentation repair.

The processing and initial testing of a new human tissue preparation is described. Full-thickness Acellular Dermal Matrix (ftADM) is the extracellular matrix (ECM) obtained by decellularization of full-thickness human skin from cadaveric donors. The safety, stability and usability of the graft are discussed with respect to the results of the residual cellular content, maintenance of ECM components, and biomechanical properties. Quantitative and qualitative analysis of the ECM demonstrated the absence of cell debris, while the native structure of human dermis was maintained. Biomechanical testing showed stiffness values comparable to other commercial products used for tendon reinforcement, suggesting that our ftADM could be successfully used not only in soft tissue regeneration surgeries, but also in tendon reinforcement. First case of ftADM in rotator cuff augmentation is described. Technical management of the patch during surgery and clinical outcomes are discussed.

[Benefits of epidural analgesia in major neonatal surgery]. / Ventajas de la analgesia epidural en cirugía mayor neonatal.

The aim of this paper is to describe and evaluate the benefits of epidural anesthesia in major surgery neonatal. We have performed a matched case-control (2:1) study of patients undergoing neonatal major surgery (NMSs) who received intra-and postoperative epidural anesthesia (EA) and controls with conventional general anesthesia. The matching criteria were age, weight and baseline pathology. EA was administered by caudal puncture and epidural catheter placed with ultrasound support. Levobupivacaine was selected as anesthetic drug. The time to extubation, intestinal transit time, type of analgesia and complications were studied. This study is based on 11 cases (2 esophageal atresia, 2 diaphragmatic hernias, 1 necrotizing enterocolitis, 3 intestinal atresia, 2 anorectal malformation and 1 bladder exstrophy) and 22 controls. We observed statistically significant differences in time to extubation (95% CI OR 12 1.99 to 72.35; Chi2 p = 0.004, Mann U Whytney p = 0.013) and intestinal transit time (Mann Whitney U p < 0.001, 100 Or, 95% CI 8.06-1 239; Chi2 p < 0.0001). There were no complications from epidural analgesia. Therefore we believe that the intra-and postoperative EA helps improve postoperative management in neonates and should be preferred in centers where this technique is available.

[When a peritonitis does not seems like a peritonitis]. / Cuando una peritonitis no parece una peritonitis.

Acute pancreatitis should be considered in the differential diagnosis of acute abdominal pain. Although its incidence is low, it has increased in the last years; therefore, an accurate diagnosis is necessary to avoid inappropriate surgeries. The aim of this study is to describe acute pancreatitis in the context of acute abdominal pain, which suggests appendicitis. We performed a retrospective study of all the patients who were admitted in the emergency department due to suspected appendicitis but were finally diagnosed of acute pancreatitis since 2010. Five patients were included in the investigation. One of them underwent surgery and the diagnosis was made on the 5th postoperative day. Median age at diagnosis was 5 years (range from 8 month to 6 years). Median white blood cell was 16,600/microL (13,400-31,900/microL), Median differential count of white blood cell was 14,432/microL (11,400-29,348/microL) and Median PCR 11 mg/L (155-4.6 mg/L). Median serum amylase at diagnosis was 651 U/L (10-1,443 U/L). All cases were studied with ultrasound and computerized tomography or nuclear magnetic resonance. One case had recurrent episodes of pancreatitis and was complicated by the development of a pseudocyst and a pancreatic fistula, requiring an Y-en-Roux cysto-enteric anastomosis. The median follow up period was 10 months (range: 1 to 22). All patients are asymptomatic at the moment.

[Using Kehr's tube in complex anastomoses]. / Utilización de tubo de Kehr en anastomosis intestinales complejas.

OBJECTIVE: To present a new technique using the Kehr's T tube (KT) in complex intestinal anastomoses. MATERIALS AND METHODS: Restrospective descriptive analysis of 8 patients intervened from 2007 to 2011. We performed intestinal anastomoses guided by a KT in 7 patients with intestinal atresia (yeyunal n = 5, ileal n = 1, duodenal n = 1), and in 1 patient with yeyunal stenosis associated with gastroschisis. 4 cases (50%) were reoperations because of complications after the first surgery. SURGICAL TECHNIQUE: the KT is introduced through the dilated proximal bowel. The proximal end of the "T" is tied and the distal one acts as a transanastomotic guide and feeding tube. The long end of the T is externalized through the skin and used for the administration of the enteral nutrition formula. Studied variables were: beginning of enteral feeding, feeding time through the KT, time of intestinal motility recovery, time to complete oral feeding and complications. RESULTS: There were no complications derived from the technique. Feeding was started through the KT between day 2 and 10 (median: 4.5), with a period of 4 to 33 days (median: 7). Patients started intestinal transit between days 2 and 7 (median: 3.5). Reoperated patients showed cholestasis and/or sepsis signs, which were solved with surgery. The KT was left in place between 11-51 days (median: 22), with no complications during or after the removal. CONCLUSIONS: The results of this preliminary study suggests that the use of the KT in complex anastomoses as a transanastomotic guide and feeding tube presents advantages, such as early enteral feeding and prevention of leakage and kinking of the intestinal suture. There were no complications derived from the procedure. As far as we know, this technique has not been previously reported in the literature.

Living in endemic area for infectious diseases accelerates epigenetic age.

Inflammaging is a low-grade inflammatory state generated by the aging process that can contribute to frailty and age-related diseases in the elderly. However, it can have distinct effects in the elderly living in endemic areas for infectious diseases. An increased inflammatory response may confer protection against infectious agents in these areas, although this advantage can cause accelerating epigenetic aging. In this study, we evaluated the inflammatory profile and the epigenetic age of infected and noninfected individuals from an endemic area in Brazil. The profile of cytokines, chemokines and growth factors analyzed in the sera of the two groups of individuals showed similarities, although infected individuals had a higher concentration of these mediators. A significant increase in IL-1ra, CXCL8, CCL2, CCL3 and CCL4 production was associated with leprosy infection. Notably, elderly individuals displayed distinct immune responses associated with their infection status when compared to adults suggesting an adaptive remodelling of their immune responses. Epigenetic analysis also showed that there was no difference in epigenetic age between the two groups of individuals. However, individuals from the endemic area had a significant accelerated aging when compared to individuals from São Paulo, a non-endemic area in Brazil. Moreover, the latter cohort was also epigenetically aged in relation to an Italian cohort. Our data shows that living in endemic areas for chronic infectious diseases results in remodelling of inflammaging and acceleration of epigenetic aging in individuals regardless of their infectious status. It also highlights that geographical, genetic and environmental factors influence aging and immunosenescence in their pace and profile.

Transcriptional regulation of lipid homeostasis in mycobacteria.

Mycolic acids are major components of the cell envelope of mycobacteria, such as Mycobacterium tuberculosis, and play an important role in its architecture, impermeability and interaction with the environment. Synthesis of mycolic acids is carried out by two types of fatty acid synthases (FAS) working in concert: type I FAS, a multifunctional enzyme capable of de novo synthesis of medium-chain fatty acids, and type II FAS, responsible for their elongation. In this article we report the identification and characterization of a transcriptional regulator (MabR), whose binding to the FAS-II promoter region was demonstrated in vitro and in vivo. Overexpression and knock-down studies in Mycobacterium smegmatis revealed the repressor nature of MabR, with reduced amounts of FAS-II transcripts and fatty acids in the overproducing strain. Under these conditions, downregulation of fas transcription was also observed, thereby suggesting the existence of cross-talk between the two FAS, mediated by MabR. Finally, the finding that a mabR knock-out mutant could only be obtained in a merodiploid strain of M. smegmatis, confirmed the predicted essentiality, thus implying an essential role for MabR in mycobacterial fatty acid metabolism.