Biology subjects

Renzi, F.

Publications and source records attributed to Renzi, F..

6 recordsLinked to original sources

bioRxiv2024

TamL is a key player of the outer membrane homeostasis in Bacteroidetes.

In Proteobacteria, the outer membrane protein TamA and the inner membrane-anchored protein TamB form the Translocation and Assembly Module (TAM) complex, which facilitates the transport of autotransporters, virulence factors, and likely lipids across the two membranes. In Bacteroidetes TamA is replaced by TamL, a TamA-like lipoprotein with a lipid modification at its N-terminus that likely anchors it to the outer membrane. This structural difference suggests that TamL may have a distinct function compared to TamA. However, the role of TAM in bacterial phyla other than Proteobacteria remains unexplored. Our study aimed to elucidate the functional importance of TamL in Flavobacterium johnsoniae, an environmental Bacteroidetes. Unlike its homologues in Proteobacteria, we found that TamL and TamB are essential in F. johnsoniae. Through genetic, phenotypic, proteomic, and lipidomic analyses, we discovered that TamL depletion severely compromises outer membrane integrity, as evidenced by reduced cell viability, altered cell shape, increased susceptibility to membrane-disrupting agents, and elevated levels of outer membrane lipoproteins. Notably, we did not observe any impact on outer membrane lipid composition. Via pull-down protein assays, we confirmed that TamL interacts with TamB in F. johnsoniae, likely forming the TAM complex. Furthermore, our in silico analysis revealed that the presence of TamL and TamB monocistronic genes is a shared genetic feature among Bacteroidetes members, including the human pathogen Capnocytophaga canimorsus where we also confirmed the essentiality of the TamL and TamB homologs. To our knowledge, this study is the first to provide functional insights into a TAM subunit beyond Proteobacteria. SignificanceIn Proteobacteria, the outer membrane (OM) protein TamA forms with the inner membrane (IM)-anchored protein TamB the Translocation and Assembly Module Complex (TAM). which contributes to efficient biogenesis of the OM. In Bacteroidetes TamA is replaced by TamL, a TamA-like lipoprotein of unknown role. In this work, we studied TamL in the Bacteroidetes Flavobacterium johnsoniae. We found that TamL and TamB are essential for cell viability, and that TamL depletion disrupts outer membrane stability, increases outer membrane vesicle size, and lead to higher sensitivity to OM stressors. These findings highlight TamL critical role in maintaining OM structure in Bacteroidetes. To our surprise, we also identified multiple TamL, TamB and TamA homologs in Bacteroidetes. Altogether, our findings extend the current knowledge on TAM and provide novel insights into a field of research barely investigated outside Proteobacteria.

microbiology↗

bioRxiv2024

Investigating the right heart hemodynamics in the Tetralogy of Fallot: a computational study

Characterizing flow within the right heart (RH) is particularly challenging due to its complex geometries. However, gaining insight into RH fluid dynamics is of extreme diagnostic importance given the high prevalence of acquired and congenital heart diseases with impaired RH functionality. In this study, we present a comprehensive, patient-specific, image-based computational analysis of the hemodynamics of the RH in healthy and repaired-ToF (ToF) cases. From multi-series cine-MTRI, we reconstruct the geometry and motion of the patients right atrium, ventricle, and pulmonary and tricuspid valves. For this purpose, we develop a novel and flexible reconstruction procedure that enables us, for the first time, to integrate fully patient-specific tricuspid valve dynamics into a computational model, enhancing the accuracy of our RH blood flow simulations. This work provides novel insight into the altered hemodynamics of repaired-ToF RH with severe pulmonary regurgitation and into the hemodynamics changes induced by the pulmonary valve replacement intervention. Modelling the whole RH enables us to understand the contribution of the superior and inferior vena cava inflows to the ventricular filling, as well as the impact of the impaired right atrial function on the ventricular diastole. We analyze the turbulent and transitional behaviour by including the Large-Eddies Simulation sigma model in our computational framework. This highlights how the contribution of the smallest scales in the dissipation of the turbulent energy changes among health and disease.

bioengineering↗

bioRxiv2024

LolA and LolB are conserved in Bacteroidetes and are crucial for gliding motility and Type IX secretion.

In Gram-negative bacteria, lipoproteins are major components of the outer membrane (OM) where they play a variety of roles, from the involvement in membrane biogenesis to virulence. Bacteroidetes, a widespread phylum of Gram-negative bacteria, including free-living organisms, commensals and pathogens, encode an exceptionally high number of outer membrane lipoproteins. These proteins are crucial in this phylum mainly because they are key components of SUS-like nutrient acquisition systems as well as of the Type 9 secretion (T9SS) and gliding motility machineries. The transport of lipoproteins to the OM has mainly been studied in E. coli and relies on the Lol system, composed of the inner membrane extraction machinery LolCDE, the periplasmic carrier LolA and the OM lipoprotein LolB. While most Lol proteins are essential and conserved across Gram-negative bacteria, to date, no LolB homologs have been identified outside of {gamma}- and {beta}-proteobacteria. How lipoproteins reach and are inserted in the OM of Bacteroidetes is not known. Here we identified LolB homologs in Bacteroidetes and disclosed the co-existence of several LolA and LolB in several species. We provide evidence that one LolA (LolA1) and one LolB (LolB1) of F. johnsoniae are devoted to targeting gliding and T9SS lipoproteins to the OM. A proteomic analysis of the OM composition of the lolA1 and lolB1 mutants supports this evidence. Furthermore, we show that, while LolB1 and LolA1 have conserved functions in Bacteroidetes, they are functionally different from their E. coli counterparts. We also show that surface lipoprotein transport is LolA and LolB independent. Finally, the finding that, in the absence of LolA and LolB homologs, lipoproteins still localize to the OM, suggests the presence in Bacteroidetes of yet unidentified LolAB-alternative lipoprotein transport pathways. In conclusion, Bacteroidetes have evolved different and more complex lipoprotein transport pathways than other Gram-negative bacteria and further research is required to uncover their complexity. SignificanceIn Gram-negative bacteria, lipoproteins are key components of the outer membrane (OM), essential for functions like membrane biogenesis and virulence. Bacteroidetes, a widespread phylum, encode a high number of OM lipoproteins crucial for nutrient acquisition, Type IX secretion, and gliding motility. While lipoprotein transport in E. coli depends on the Lol system, LolB homologs were previously unidentified outside {gamma}- and {beta}-proteobacteria. Here we identify LolB homologs in Bacteroidetes, revealing the co-existence of multiple LolA and LolB proteins in various species. In F. johnsoniae, LolA1 and LolB1 specifically target gliding and Type 9 secretion system lipoproteins to the OM. Despite this, lipoproteins still localize to the OM without LolA and LolB, suggesting alternative transport pathways. These findings indicate that Bacteroidetes have evolved more complex lipoprotein transport mechanisms than other Gram-negative bacteria, requiring further research to fully understand them.

microbiology↗

bioRxiv2023

Accurate and Efficient 3D Reconstruction of Right Heart Shape and Motion from Multi-Series Cine-MRI

The accurate reconstruction of the right heart geometry and motion from time-resolved medical images enhances diagnostic tools based on image visualization as well as the analysis of cardiac blood dynamics through computational methods. Due to the peculiarity of the right heart morphology and motion, commonly used segmentation and/or reconstruction techniques, which only employ Short-Axis cine-MRI, lack accuracy in relevant regions of the right heart, like the ventricular base and the outflow tract. Moreover, the reconstruction procedure is time-consuming and, in the case of the generation of computational domains, requires a lot of manual intervention. This paper presents a new method for the accurate and efficient reconstruction of the right heart geometry and motion from time-resolved MRI. In particular, the proposed method makes use of surface morphing to merge information coming from multi-series cine-MRI (such as Short/Long-Axis and 2/3/4 Chambers acquisitions) and to reconstruct important cardiac features. It also automatically provides the complete cardiac contraction and relaxation motion by exploiting a suitable image registration technique. The method is applied both to a healthy and a pathological (tetralogy of Fallot) case, and yelds more accurate results than standard procedures. The proposed method is also employed to provide significant input for computational fluid dynamics. The corresponding numerical results demonstrate the reliability of our approach in the computation of clinically relevant blood dynamics quantities.

bioengineering↗

bioRxiv2023

Turbulence and blood washout in presence of mitral regurgitation: a computational fluid-dynamics study in the complete left heart

In this work we performed a computational image-based study of blood dynamics in the whole left heart, both in a healthy subject and in a patient with mitral valve regurgitation (MVR). We elaborated dynamic cine-MRI images with the aim of reconstructing the geometry and the corresponding motion of left ventricle, left atrium, mitral and aortic valves, and aortic root of the subjects. This allowed us to prescribe such motion to computational blood dynamics simulations where, for the first time, the whole left heart motion of the subject is considered, allowing us to obtain reliable subject-specific information. The final aim is to investigate and compare between the subjects the occurrence of turbulence and the risk of hemolysis and of thrombi formation. In particular, we modeled blood with the Navier-Stokes equations in the Arbitrary Lagrangian-Eulerian framework, with a Large Eddy Simulation model to describe the transition to turbulence and a resistive method to manage the valve dynamics, and we used a Finite Elements discretization implemented in an in-house code for the numerical solution. Our results highlighted that the regurgitant jet in the MVR case gave rise to a large amount of transition to turbulence in the left atrium resulting in a higher risk of formation of hemolysis. Moreover, MVR promoted a more complete washout of stagnant fiows in the left atrium during the systolic phase and in the left ventricle apex during diastole. NEW & NOTEWORTHYReconstruction from cine-MRI images of geometries and motion of the left heart (left atrium and ventricle, aortic root, aortic and mitral valve) of a healthy and mitral regurgitant patient. Prescription of such motion to a complete subject-specific computational fluid-dynamic simulation of the left heart. Investigation of turbulence in a regurgitant scenario. Study of the mechanisms of prevention from stagnant flows and hemolysis formation in the atrium.

bioengineering↗

bioRxiv2020

ACE2 fragment as a decoy for novel SARS-Cov-2 virus

Novel SARS-Cov-2 enters human cells via interaction between the surface spike (S) glycoprotein and the cellular membrane receptor angiotensin-converting enzyme 2 (ACE2). Using a combination of comparative structural analyses of the binding surface of the S protein to ACE2, docking experiments, and molecular dynamics simulations we computationally identified a minimal, stable fragment of ACE2. This fragment binds to the S protein, is soluble, and appears not to bind to the physiological ligand angiotensinII. These results suggest a possible use of the ACE2 fragment as a decoy that could interfere with viral binding by competition.

bioinformatics↗