Novel insights into SLC25A46-related pathologies in a genetic mouse model.

The mitochondrial protein SLC25A46 has been recently identified as a novel pathogenic cause in a wide spectrum of neurological diseases, including inherited optic atrophy, Charcot-Marie-Tooth type 2, Leigh syndrome, progressive myoclonic ataxia and lethal congenital pontocerebellar hypoplasia. SLC25A46 is an outer membrane protein, member of the Solute Carrier 25 (SLC25) family of nuclear genes encoding mitochondrial carriers, with a role in mitochondrial dynamics and cristae maintenance. Here we identified a loss-of-function mutation in the Slc25a46 gene that causes lethal neuropathology in mice. Mutant mice manifest the main clinical features identified in patients, including ataxia, optic atrophy and cerebellar hypoplasia, which were completely rescued by expression of the human ortholog. Histopathological analysis revealed previously unseen lesions, most notably disrupted cytoarchitecture in the cerebellum and retina and prominent abnormalities in the neuromuscular junction. A distinct lymphoid phenotype was also evident. Our mutant mice provide a valid model for understanding the mechanistic basis of the complex SLC25A46-mediated pathologies, as well as for screening potential therapeutic interventions.

Targeting Mitochondrial Network Architecture in Down Syndrome and Aging.

Mitochondria are organelles that mainly control energy conversion in the cell. In addition, they also participate in many relevant activities, such as the regulation of apoptosis and calcium levels, and other metabolic tasks, all closely linked to cell viability. Functionality of mitochondria appears to depend upon their network architecture that may dynamically pass from an interconnected structure with long tubular units, to a fragmented one with short separate fragments. A decline in mitochondrial quality, which presents itself as an altered structural organization and a function of mitochondria, has been observed in Down syndrome (DS), as well as in aging and in age-related pathologies. This review provides a basic overview of mitochondrial dynamics, from fission/fusion mechanisms to mitochondrial homeostasis. Molecular mechanisms determining the disruption of the mitochondrial phenotype in DS and aging are discussed. The impaired activity of the transcriptional co-activator PGC-1α/PPARGC1A and the hyperactivation of the mammalian target of rapamycin (mTOR) kinase are emerging as molecular underlying causes of these mitochondrial alterations. It is, therefore, likely that either stimulating the PGC-1α activity or inhibiting mTOR signaling could reverse mitochondrial dysfunction. Evidence is summarized suggesting that drugs targeting either these pathways or other factors affecting the mitochondrial network may represent therapeutic approaches to improve and/or prevent the effects of altered mitochondrial function. Overall, from all these studies it emerges that the implementation of such strategies may exert protective effects in DS and age-related diseases.

Human Trisomic iPSCs from Down Syndrome Fibroblasts Manifest Mitochondrial Alterations Early during Neuronal Differentiation.

BACKGROUND: The presence of mitochondrial alterations in Down syndrome suggests that it might affect neuronal differentiation. We established a model of trisomic iPSCs, differentiating into neural precursor cells (NPCs) to monitor the occurrence of differentiation defects and mitochondrial dysfunction. METHODS: Isogenic trisomic and euploid iPSCs were differentiated into NPCs in monolayer cultures using the dual-SMAD inhibition protocol. Expression of pluripotency and neural differentiation genes was assessed by qRT-PCR and immunofluorescence. Meta-analysis of expression data was performed on iPSCs. Mitochondrial Ca2+, reactive oxygen species (ROS) and ATP production were investigated using fluorescent probes. Oxygen consumption rate (OCR) was determined by Seahorse Analyzer. RESULTS: NPCs at day 7 of induction uniformly expressed the differentiation markers PAX6, SOX2 and NESTIN but not the stemness marker OCT4. At day 21, trisomic NPCs expressed higher levels of typical glial differentiation genes. Expression profiles indicated that mitochondrial genes were dysregulated in trisomic iPSCs. Trisomic NPCs showed altered mitochondrial Ca2+, reduced OCR and ATP synthesis, and elevated ROS production. CONCLUSIONS: Human trisomic iPSCs can be rapidly and efficiently differentiated into NPC monolayers. The trisomic NPCs obtained exhibit greater glial-like differentiation potential than their euploid counterparts and manifest mitochondrial dysfunction as early as day 7 of neuronal differentiation.

Giant Heterometallic [Mn36Ni4]0/2- and [Mn32Co8] "Loops-of-Loops-and-Supertetrahedra" Molecular Aggregates.

We report the synthesis, crystal structures and magnetic properties of the giant heterometallic [Mn36Ni4]2-/0 (compounds 1, 2)/[Mn32Co8] (compound 3) "loops-of-loops-and-supertetrahedra" molecular aggregates and of a [Mn2Ni6]2+ compound (cation of 4) that is structurally related with the cation co-crystallizing with the anion of 1. In particular, after the initial preparation and characterization of compound [Mn2Ni6(µ4-O)2(µ3-OH)3(µ3-Cl)3(O2CCH3)6(py)8]2+[Mn36Ni4(µ4-O)8(µ3-O)4(µ3-Cl)8Cl4(O2CCH3)26(pd)24(py)4]2- (1) we targeted the isolation of (i) both the cationic and the anionic aggregates of 1 in a discrete form and (ii) the Mn/Co analog of [Mn36Ni4]2- aggregate. Our synthetic efforts toward these directions afforded the discrete [Mn36Ni4] "loops-of-loops-and-supertetrahedra" aggregate [Mn36Ni4(µ4-O)8(µ3-O)4(µ3-Cl)8Cl2(O2CCH3)26(pd)24(py)4(H2O)2] (2), the heterometallic Mn/Co analog [Mn32Co8(µ4-O)8(µ3-O)4(µ3-Cl)8Cl2(µ2-OCH2CH3)2(O2CCH3)28(pd)22(py)6] (3) and the discrete [Mn2Ni6]2+ cation [Mn2Ni6(µ4-O)2(µ3-OH)4(µ3-Cl)2(O2CCH3)6(py)8](ClO4)(OH) (4). The structure of 1 consists of a mixed valence [ Mn 28 III Mn 8 II Ni 4 II ]2- molecular aggregate that contains two Mn 8 III Ni 2 II loops separated by two Mn 6 III Mn 4 II supertetrahedral units and a [ Mn 2 III Ni 6 II ]2+ cation based on two [MnIII Ni 3 II (µ4-O)(µ3-OH)1.5(µ3-Cl)1.5]4+ cubane sub-units connected through both mono- and tri-atomic bridges provided by the µ4-O2- and carboxylate anions. The structures of 2-4 are related to those of the compounds co-crystallized in 1 exhibiting however some differences that shall be discussed in detail in the manuscript. Magnetism studies revealed the presence of dominant ferromagnetic interactions in 1-3 that lead to large ground state spin (ST) values for the "loops-of-loops-and-supertetrahedra" aggregates and antiferromagnetic exchange interactions in 4 that lead to a low (and possibly zero) ST value. In particular, dc and ac magnetic susceptibility studies revealed that the discrete [Mn36Ni4] aggregate exhibits a large ST value ~ 26 but is not a new SMM. The ac magnetic susceptibility studies of the [Mn32Co8] analog revealed an extremely weak beginning of an out-of-phase tail indicating the presence of a very small relaxation barrier assignable to the anisotropic Co2+ions and a resulting out-of-phase ac signal whose peak is at very low T.

The triterpene echinocystic acid and its 3-O-glucoside derivative are revealed as potent and selective glucocorticoid receptor agonists.

Glucocorticoids are steroid hormones widely used to control many inflammatory conditions. These effects are primarily attributed to glucocorticoid receptor transrepressional activities but with concomitant receptor transactivation associated with considerable side effects. Accordingly, there is an immediate need for selective glucocorticoid receptor agonists able to dissociate transactivation from transrepression. Triterpenoids have structural similarities with glucocorticoids and exhibit anti-inflammatory and apoptotic activities via mechanisms that are not well-defined. In this study, we examined whether echinocystic acid and its 3-O-glucoside derivative act, at least in part, through the regulation of glucocorticoid receptor and whether they can constitute selective receptor activators. We showed that echinocystic acid and its glucoside induced glucocorticoid receptor nuclear translocation by 75% and 55%. They suppressed the nuclear factor-kappa beta transcriptional activity by 20% and 70%, respectively, whereas they have no glucocorticoid receptor transactivation capability and stimulatory effect on the expression of the phosphoenolopyruvate carboxykinase target gene in HeLa cells. Interestingly, their suppressive effect is diminished in glucocorticoid receptor low level COS-7 cells, verifying the receptor involvement in this process. Induced fit docking calculations predicted favorable binding in the ligand binding domain and structural characteristics which can be considered consistent with the experimental observations. Further, glucocorticoids exert apoptotic activities; we have demonstrated here that the echinocystic acids in combination with the synthetic glucocorticoid, dexamethasone, induce apoptosis. Taken together, our results indicate that echinocystic acids are potent glucocorticoid receptor regulators with selective transrepressional activities (dissociated from transactivation), highlighting the potential of echinocystic acid derivatives as more promising treatments for inflammatory conditions.

Discrete and encapsulated molecular grids: homometallic Mn15 and heterometallic Mn24Ni2 aggregates.

Two molecular grid-like clusters are reported, one is a discrete [3 × 5] grid and the other a [3 × 4] grid within a Mn12Ni2 loop. Both Mn24Ni2 and Mn15 aggregates display novel and aesthetically pleasing structures with the former one being among the highest nuclearity heterometallic MnxMy clusters (M = any transition metal ion).

A Mn36Ni4 'loop-of-loops-and-supertetrahedra' aggregate possessing a high S(T) = 26 ± 1 spin ground state.

The initial use of 1,3-propanediol in mixed Mn/3d cluster chemistry has led to a Mn(III)(28)Mn(II)(8)Ni(II)(4) molecular aggregate which consists of two Mn(III)(8)Ni(2) loops and two Mn(III)(6)Mn(II)(4) supertetrahedral units and displays a high ground spin state value S(T) = 26 ± 1.