Different prelamin A forms accumulate in human fibroblasts: a study in experimental models and progeria

Lamin A is a component of the nuclear lamina mutated in a group of human inherited disorders known as laminopathies. Among laminopathies, progeroid syndromes and lipodystrophies feature accumulation of prelamin A, the precursor protein which, in normal cells, undergoes a multi-step processing to yield mature lamin A. It is of utmost importance to characterize the prelamin A form accumulated in each laminopathy, since existing evidence shows that drugs acting on protein processing can improve some pathological aspects. We report that two antibodies raised against differently modified prelamin A peptides show a clear specificity to full-length prelamin A or carboxymethylated farnesylated prelamin A, respectively. Using these antibodies, we demonstrated that inhibition of the prelamin A endoprotease ZMPSTE24 mostly elicits accumulation of full-length prelamin A in its farnesylated form, while loss of the prelamin A cleavage site causes accumulation of carboxymethylated prelamin A in progeria cells. These results suggest a major role of ZMPSTE24 in the first prelamin A cleavage step

Multiple Peaks in the Angular Power Spectrum of the Cosmic Microwave Background: Significance and Consequences for Cosmology

Three peaks and two dips have been detected in the power spectrum of the cosmic microwave background from the BOOMERANG experiment, at $\ell \sim 210, 540, 840$ and $\ell \sim 420, 750$, respectively. Using model-independent analyses, we find that all five features are statistically significant and we measure their location and amplitude. These are consistent with the adiabatic inflationary model. We also calculate the mean and variance of the peak and dip locations and amplitudes in a large 7-dimensional parameter space of such models, which gives good agreement with the model-independent estimates, and forecast where the next few peaks and dips should be found if the basic paradigm is correct. We test the robustness of our results by comparing Bayesian marginalization techniques on this space with likelihood maximization techniques applied to a second 7-dimensional cosmological parameter space, using an independent computational pipeline, and find excellent agreement: $\Omega_{\rm tot} = 1.02^{+0.06}_{-0.05}$ {\it vs.} $1.04 \pm 0.05$, $\Omega_b h^2 = 0.022^{+0.004}_{-0.003}$ {\it vs.} $0.019^{+0.005}_{-0.004}$, and $n_s = 0.96^{+0.10}_{-0.09}$ {\it vs.} $0.90 \pm 0.08$. The deviation in primordial spectral index $n_s$ is a consequence of the strong correlation with the optical depth

Altered adipocyte differentiation and unbalanced autophagy in type 2 Familial Partial Lipodystrophy: an in vitro and in vivo study of adipose tissue browning

Type-2 Familial Partial Lipodystrophy is caused by LMNA mutations. Patients gradually lose subcutaneous fat from the limbs, while they accumulate adipose tissue in the face and neck. Several studies have demonstrated that autophagy is involved in the regulation of adipocyte differentiation and the maintenance of the balance between white and brown adipose tissue. We identified deregulation of autophagy in laminopathic preadipocytes before induction of differentiation. Moreover, in differentiating white adipocyte precursors, we observed impairment of large lipid droplet formation, altered regulation of adipose tissue genes, and expression of the brown adipose tissue marker UCP1. Conversely, in lipodystrophic brown adipocyte precursors induced to differentiate, we noticed activation of autophagy, formation of enlarged lipid droplets typical of white adipocytes, and dysregulation of brown adipose tissue genes. In agreement with these in vitro results indicating conversion of FPLD2 brown preadipocytes toward the white lineage, adipose tissue from FPLD2 patient neck, an area of brown adipogenesis, showed a white phenotype reminiscent of its brown origin. Moreover, in vivo morpho-functional evaluation of fat depots in the neck area of three FPLD2 patients by PET/CT analysis with cold stimulation showed the absence of brown adipose tissue activity. These findings highlight a new pathogenetic mechanism leading to improper fat distribution in lamin A-linked lipodystrophies and show that both impaired white adipocyte turnover and failure of adipose tissue browning contribute to disease.We thank FPLD2 patients for donating biological samples. We thank the Italian Network for Laminopathies and the European Consortium of Lipodystrophies (ECLip) for support and helpful discussion. We thank Aurelio Valmori for the technical support. The studies were supported by Rizzoli Orthopedic Institute “5 per mille” 2014 project to MC, AIProSaB project 2016 and Fondazione Del Monte di Bologna e Ravenna grant 2015–2016 “New pharmacological approaches in bone laminopathies based on the use of antibodies neutralizing TGF beta 2” to GL. GL is also supported by PRIN MIUR project 2015FBNB5Y.S

Les lipodystrophies génétiques

Les lipodystrophies d’origine génétique sont des entités rares. Il s’agit d’un groupe de maladies monogéniques, pour lesquelles plusieurs gènes différents ont été mis en cause. Cliniquement, les syndromes lipodystrophiques associent insulino-résistance, troubles du développement ou de la répartition du tissu adipeux et dyslipidémies majeures. Les lipodystrophies sont classées selon le caractère généralisé ou partiel de la lipoatrophie : – Le syndrome de Berardinelli-Seip ou lipoatrophie congénitale généralisée Il est le plus souvent lié à aux mutations de la seipine, ou d’AGPAT2, enzyme de la voie de synthèse des triglycérides adipocytaires. Plus rarement, des mutations de la cavéoline 1 ou de la cavine 1, qui appartiennent à des invaginations membranaires appelées caveolae, et qui sont des protéines structurales de la gouttelette lipidique adipocytaire un rôle dans la formation de la gouttelette lipidique adipocytaire, ont été rapportées dans des syndromes de Berardinelli-Seip. – Le syndrome de Dunnigan ou lipodystrophie partielle familiale. Il est lié le plus souvent aux mutations du gène de la lamine A/C, protéine ubiquitaire du réseau filamentaire de la lamina, situé sous la membrane interne du noyau cellulaire, ou du gène du PPARg, facteur transcriptionnel adipogénique. Des mutations dans d’autres gènes rendent compte d’autres cas, plus rares; il s’agit des gènes codant pour AkT2 (intermédiaire de la voie de signalisation insulinique), CIDEC (protéine de la gouttelette lipidique adipocytaire), ou la périlipine, qui structure la gouttelette et régule la lipolyse adipocytaire, et dont l’implication dans certaines lipodystrophies partielles autosomales dominantes vient d’être montrée. – D’autres mutations de la lamine A/C donnent des syndromes d’insulino-résistance avec lipodystrophie atypique, parfois minime (laminopathies métaboliques) et des syndromes de lipodystrophies partielles ou généralisées dans le cadre de syndromes de vieillissement accélérés (dysplasie acromandibulaire, progéria), pouvant aussi être liés à des mutations d’une l’enzyme de maturation de la prélamine A en lamine A, ZMPSTE24. – D’autres syndromes lipodystrophiques familiaux, généralisés ou partiels, restent de cause inconnue : le rôle d’autres gènes reste à découvrir. L’identification des phénotypes et des génotypes de ces pathologies est encore incomplète mais ces maladies, diverses, génétiquement déterminées, sont des modèles pour l’étude du déterminisme plus général de la résistance à l’insuline. Le traitement est identique au traitement des autres situations d’insulino-résistance : exercice physique, insulino-sensibilisateurs, insuline. Il doit également rendre en charge l’ensemble des facteurs de risque cardio-vasculaires. Des essais cliniques de traitement par la leptine sont encourageants

Microtubule cytoskeleton regulates connexin 43 localization and cardiac conduction in cardiomyopathy caused by mutation in A-type lamins gene

Mutations in the lamin A/C gene (LMNA) cause an autosomal dominant inherited form of dilated cardiomyopathy associated with cardiac conduction disease (hereafter referred to as LMNA cardiomyopathy). Compared with other forms of dilated cardiomyopathy, mutations in LMNA are responsible for a more aggressive clinical course due to a high rate of malignant ventricular arrhythmias. Gap junctions are intercellular channels that allow direct communication between neighboring cells, which are involved in electrical impulse propagation and coordinated contraction of the heart. For gap junctions to properly control electrical synchronization in the heart, connexin-based hemichannels must be correctly targeted to intercalated discs, Cx43 being the major connexin in the working myocytes. We here showed an altered distribution of Cx43 in a mouse model of LMNA cardiomyopathy. However, little is known on the molecular mechanisms of Cx43 remodeling in pathological context. We now show that microtubule cytoskeleton alteration and decreased acetylation of α-tubulin lead to remodeling of Cx43 in LMNA cardiomyopathy, which alters the correct communication between cardiomyocytes, ultimately leading to electrical conduction disturbances. Preventing or reversing this process could offer a strategy to repair damaged heart. Stabilization of microtubule cytoskeleton using Paclitaxel improved intraventricular conduction defects. These results indicate that microtubule cytoskeleton contributes to the pathogenesis of LMNA cardiomyopathy and that drugs stabilizing the microtubule may be beneficial for patients