Biology subjects

Khemtemourian, L.

Publications and source records attributed to Khemtemourian, L..

5 recordsLinked to original sources

bioRxiv2024

The amyloid oligomer modulator anle138b has disease modifying effects in a human IAPP transgenic mouse model of type 2 diabetes mellitus (hIAPP Ob/Ob mice)

Aims/HypothesisType 2 diabetes mellitus (T2DM) is a common metabolic disease, characterized by impaired insulin action, often called "insulin resistance", in conjunction with a decline in insulin secretion by the pancreatic islet beta cells, referred to as "beta cell failure". Both conditions contribute to causing hyperglycemia, which is the central feature of T2DM. Cytotoxic aggregates of the beta cell hormone human islet amyloid polypeptide (hIAPP), promote T2DM pathogenesis by damaging the pancreatic islet beta cells and reducing insulin secretion. Anle138b is an amyloid oligomer modulator with demonstrated disease-modifying properties in mouse models of neurodegenerative diseases linked to protein aggregation, and is currently in a phase 2 clinical trial. We therefore tested whether anle138b can reduce hyperglycemia in a severe hIAPP transgenic mouse model of T2DM. MethodsAnle138b was administered orally via dietary admixture to male hIAPP Ob/Ob mice and Ob/Ob controls; blood glucose-, insulin-, and glycated hemoglobin (HbA1c) levels were measured at different timepoints over 34 weeks; in addition, the effects of anle138b on the histomorphology of the pancreatic islets was determined. Finally, anle138b effects on mitochondrial toxicity of hIAPP aggregates was assessed in vitro. ResultsOral administration of anle138b in male hIAPP Ob/Ob mice potently reduced hyperglycemia and glycated HbA1c levels compared to non-treated mice (at 34 weeks, mean glucose level non-treated: 30 {+/-} 1.3 mM, treated: 15 {+/-} 2.2 mM (p < 0.001); at 32 weeks, mean HbA1c level non-treated: 77 {+/-} 3.3 mM/M, treated: 41 {+/-} 5.3 mM/M (p < 0.01)), in a hIAPP-dependent way. In addition, anle138b increased both the number of pancreatic islets as well as the overall islet beta cell mass (by 54% and 58%, respectively) in hIAPP Ob/Ob mice. In vitro, anle138b inhibited toxic effects of hIAPP on mitochondria, such as mitochondrial swelling (decreased by 92%, p < 0.01), release of cytochrome c (decreased by 63.7%, p < 0.001) and lowered mitochondrial membrane potential (increased by 62%, p < 0.001). Conclusions/InterpretationCollectively, our results indicate that anle138b is a promising clinical drug candidate for preserving islet function and reducing hyperglycemia in T2DM, in part by mitigating mitochondrial dysfunction. Research in ContextO_ST_ABSWhat is already known about this subject?C_ST_ABSO_LIType 2 diabetes mellitus (T2DM) is characterized by hyperglycemia, which stems from impaired insulin action coupled with declining insulin secretion from pancreatic islet beta cells. C_LIO_LIAggregation of the beta cell hormone human islet amyloid polypeptide (hIAPP) plays a crucial role in the loss and dysfunction of the insulin-secreting beta cells. C_LIO_LIThe small-molecule anle138b effectively modulates the aggregation of amyloidogenic proteins in neurodegenerative conditions such as Alzheimers and Parkinsons disease. C_LI What is the key question?O_LICan the oligomer modulator anle138b ameliorate the diabetic phenotype in a severe hIAPP transgenic mouse model of T2DM (hIAPP Ob/Ob) ? C_LIO_LIWhat are the new findings? C_LIO_LIOral treatment of hIAPP Ob/Ob mice with anle138b causes reduced hyperglycemia and reduced glycated hemoglobin (HbA1c) levels, in a hIAPP-dependent manner. C_LIO_LIAnle138b increases pancreatic islet number and beta cell mass and restores the inverse relation between insulin and glucose in hIAPP Ob/Ob mice. C_LIO_LIIn vitro anle138b inhibits toxic effects of hIAPP aggregates on mitochondria. C_LI How might this impact on clinical practice in the foreseeable future?O_LIAnle138b could be introduced as a promising clinical drug candidate for slowing down disease progression of T2DM. C_LI

pathology↗

bioRxiv2024

N-formylation modifies membrane damage associated to PSMα3 interfacial fibrillation

The virulence of Staphylococcus aureus, a multi-drug resistant pathogen, notably depends on the expression of the phenol soluble modulins 3 (PSM3) peptides, able to self-assemble into amyloid-like cross- fibrils. Despite remarkable advances evidencing the crucial, yet insufficient, role of fibrils in PSM3 cytotoxic activities towards host cells, the relationship between its molecular structures, assembly propensities, and modes of action remains an open intriguing problem. In this study, combining Atomic Force Microscopy (AFM) imaging and infrared spectroscopy, we first demonstrated in vitro that the charge provided by the N-terminal capping of PSM3 alters its interactions with model membranes of controlled lipid composition, without compromising its fibrillation kinetics or morphology. N-formylation eventually dictates PSM3 - membrane binding via electrostatic interactions with the lipid head groups. Furthermore, PSM3 insertion within the lipid bilayer is favoured by hydrophobic interactions with the lipid acyl chains, only in the fluid-phase of membranes, and not in the gel-like ordered domains. Strikingly, our real-time AFM imaging emphasizes how intermediate protofibrillar entities, formed along PSM3 self-assembly and promoted at the membrane interface, likely disrupt membrane integrity via peptide accumulation, and subsequent membrane thinning in a peptide concentration and lipid-dependent manner. Overall, our multiscale and multimodal approach sheds new light on the key roles of N-formylation and intermediate self-assembling entities, rather than mature fibrils, in dictating deleterious interactions of PSM3 with specific membrane lipids, likely underscoring its ultimate cellular toxicity in vivo, and in turn S. aureus pathogenesis.

biophysics↗

bioRxiv2022

Fibril elongation by human islet amyloid polypeptide is the main event linking aggregation to membrane damage

The aggregation of human islet amyloid polypeptide (hIAPP) is linked to the death of pancreatic {beta}-cells in type II diabetes. The process of fibril formation by hIAPP is thought to cause membrane damage, but the precise mechanisms are still unclear. Previously, we showed that the aggregation of hIAPP in the presence of membranes containing anionic lipids is dominated by secondary nucleation events, which occur at the interface between existing fibrils and the membrane surface. Here, we used vesicles with different lipid composition to explore the connection between hIAPP aggregation and vesicle leakage. We found that different anionic lipids promote hIAPP aggregation to the same extent, whereas remarkably stochastic behaviour is observed on purely zwitterionic membranes. Vesicle leakage induced by hIAPP consists of two distinct phases for any of the used membrane compositions: (i) an initial phase in which hIAPP binding causes a certain level of leakage that is strongly dependent on osmotic conditions, membrane composition and the used dye, and (ii) a main leakage event that we attribute to elongation of hIAPP fibrils, based on seeded experiments. Altogether, our results shed more light on the relationship between hIAPP fibril formation and membrane damage, and strongly suggest that oligomeric intermediates do not considerably contribute to vesicle leakage.

biochemistry↗

bioRxiv2022

Membrane-catalyzed IAPP aggregation is dominated by secondary nucleation

Type II diabetes is characterized by the loss of pancreatic {beta}-cells. This loss is thought to be a consequence of membrane disruption, caused by the aggregation of islet amyloid polypeptide (IAPP) into amyloid fibrils. However, the molecular mechanisms of IAPP aggregation in the presence of membranes have remained unclear. Here, we use kinetic analysis to elucidate the aggregation mechanism of IAPP in the presence of mixed zwitterionic and anionic lipid membranes. The results converge to a model in which aggregation on the membrane is strongly dominated by secondary nucleation, i.e. the formation of new nuclei on the surface of existing fibrils. The critical nucleus consists of a single IAPP molecule, and anionic lipids catalyze both primary and secondary nucleation, but not elongation. The fact that anionic lipids promote secondary nucleation implies that these events take place at the interface between the membrane and existing fibrils, demonstrating that fibril growth occurs at least to some extent on the membrane surface. These new insights into the mechanism of IAPP aggregation on membranes may help to understand IAPP toxicity and will be important for the development of therapeutics to prevent {beta}-cell death in type II diabetes.

biophysics↗

bioRxiv2021

Structural dissection of the first events following membrane binding of the islet amyloid polypeptide

Amyloid forming proteins are involved in many pathologies and often belong to the class of intrinsically disordered proteins. One of these proteins is the islet amyloid polypeptide (IAPP), which is the main constituent of the amyloid fibrils found in the pancreas of type 2 diabetes patients. The molecular mechanism of IAPP-induced cell death is not yet understood, however it is known that cell membrane plays a dual role, being a catalyst of IAPP aggregation and the target of IAPP toxicity. Using FTIR spectroscopy, transmission electron microscopy, and molecular dynamics simulations we investigate the very first molecular steps following IAPP binding to a lipid membrane. In particular, we assess the combined effects of the charge state of amino-acid residue 18 and the IAPP-membrane interactions on the structures of monomeric and aggregated IAPP. Both our experiments and simulations reveal distinct IAPP-membrane interaction modes for the various IAPP variants. Membrane binding causes IAPP to fold into an amphipathic helix, which in the case of H18K- and H18R-IAPP can easily insert into the membrane. For all IAPP variants but H18E-IAPP, the membrane-bound -helical structure is an intermediate on the way to IAPP amyloid aggregation, while H18E-IAPP remains in a stable helical conformation. The fibrillar aggregates of wild-type IAPP and H18K-IAPP are dominated by an antiparallel {beta}-sheet conformation, while H18R- and H18A-IAPP exhibit both antiparallel and parallel {beta}-sheets as well as amorphous aggregates. In summary, our results emphasize the importance of residue 18 for the structure and membrane interaction of IAPP. This residue is thus a good target for destabilizing amyloid fibrils of IAPP and inhibit its toxic actions by possible therapeutic molecules.

biophysics↗