Loss of Miro1-directed mitochondrial movement results in a novel murine model for neuron disease

Defective mitochondrial distribution in neurons is proposed to cause ATP depletion and calcium-buffering deficiencies that compromise cell function. However, it is unclear whether aberrant mitochondrial motility and distribution alone are sufficient to cause neurological disease. Calcium-binding mitochondrial Rho (Miro) GTPases attach mitochondria to motor proteins for anterograde and retrograde transport in neurons. Using two new KO mouse models, we demonstrate that Miro1 is essential for development of cranial motor nuclei required for respiratory control and maintenance of upper motor neurons required for ambulation. Neuron-specific loss of Miro1 causes depletion of mitochondria from corticospinal tract axons and progressive neurological deficits mirroring human upper motor neuron disease. Although Miro1-deficient neurons exhibit defects in retrograde axonal mitochondrial transport, mitochondrial respiratory function continues. Moreover, Miro1 is not essential for calcium-mediated inhibition of mitochondrial movement or mitochondrial calcium buffering. Our findings indicate that defects in mitochondrial motility and distribution are sufficient to cause neurological disease.Motor neuron diseases (MNDs), including ALS and spastic paraplegia (SP), are characterized by the progressive, length-dependent degeneration of motor neurons, leading to muscle atrophy, paralysis, and, in some cases, premature death. There are both inherited and sporadic forms of MNDs, which can affect upper motor neurons, lower motor neurons, or both. Although the molecular and cellular causes of most MNDs are unknown, many are associated with defects in axonal transport of cellular components required for neuron function and maintenance (1–6).A subset of MNDs is associated with impaired mitochondrial respiration and mitochondrial distribution. This observation has led to the hypothesis that neurodegeneration results from defects in mitochondrial motility and distribution, which, in turn, cause subcellular ATP depletion and interfere with mitochondrial calcium ([Ca²⁺]_m) buffering at sites of high synaptic activity (reviewed in ref. 7). It is not known, however, whether mitochondrial motility defects are a primary cause or a secondary consequence of MND progression. In addition, it has been difficult to isolate the primary effect of mitochondrial motility defects in MNDs because most mutations that impair mitochondrial motility in neurons also affect transport of other organelles and vesicles (1, 8–11).In mammals, the movement of neuronal mitochondria between the cell body and the synapse is controlled by adaptors called trafficking kinesin proteins (Trak1 and Trak2) and molecular motors (kinesin heavy chain and dynein), which transport the organelle in the anterograde or retrograde direction along axonal microtubule tracks (7, 12–24). Mitochondrial Rho (Miro) GTPase proteins are critical for transport because they are the only known surface receptors that attach mitochondria to these adaptors and motors (12–15, 18, 25, 26). Miro proteins are tail-anchored in the outer mitochondrial membrane with two GTPase domains and two predicted calcium-binding embryonic fibroblast (EF) hand motifs facing the cytoplasm (12, 13, 25, 27, 28). A recent Miro structure revealed two additional EF hands that were not predicted from the primary sequence (29). Studies in cultured cells suggest that Miro proteins also function as calcium sensors (via their EF hands) to regulate kinesin-mediated mitochondrial “stopping” in axons (15, 16, 26). Miro-mediated movement appears to be inhibited when cytoplasmic calcium is elevated in active synapses, effectively recruiting mitochondria to regions where calcium buffering and energy are needed. Despite this progress, the physiological relevance of these findings has not yet been tested in a mammalian animal model. In addition, mammals ubiquitously express two Miro orthologs, Miro1 and Miro2, which are 60% identical (12, 13). However, the individual roles of Miro1 and Miro2 in neuronal development, maintenance, and survival have no been evaluated.We describe two new mouse models that establish the importance of Miro1-mediated mitochondrial motility and distribution in mammalian neuronal function and maintenance. We show that Miro1 is essential for development/maintenance of specific cranial neurons, function of postmitotic motor neurons, and retrograde mitochondrial motility in axons. Loss of Miro1-directed retrograde mitochondrial transport is sufficient to cause MND phenotypes in mice without abrogating mitochondrial respiratory function. Furthermore, Miro1 is not essential for calcium-mediated inhibition of mitochondrial movement or [Ca²⁺]_m buffering. These findings have an impact on current models for Miro1 function and introduce a specific and rapidly progressing mouse model for MND.     

Beta cyclodextrins bind,stabilize, and remove lipofuscin bisretinoids from retinal pigment epithelium

Accumulation of lipofuscin bisretinoids (LBs) in the retinal pigment epithelium (RPE) is the alleged cause of retinal degeneration in genetic blinding diseases (e.g., Stargardt) and a possible etiological agent for age-related macular degeneration. Currently, there are no approved treatments for these diseases; hence, agents that efficiently remove LBs from RPE would be valuable therapeutic candidates. Here, we show that beta cyclodextrins (β-CDs) bind LBs and protect them against oxidation. Computer modeling and biochemical data are consistent with the encapsulation of the retinoid arms of LBs within the hydrophobic cavity of β-CD. Importantly, β-CD treatment reduced by 73% and 48% the LB content of RPE cell cultures and of eyecups obtained from Abca4-Rdh8 double knock-out (DKO) mice, respectively. Furthermore, intravitreal administration of β-CDs reduced significantly the content of bisretinoids in the RPE of DKO animals. Thus, our results demonstrate the effectiveness of β-CDs to complex and remove LB deposits from RPE cells and provide crucial data to develop novel prophylactic approaches for retinal disorders elicited by LBs.The retinal pigment epithelium (RPE), strategically situated between the neural retina and the choroid blood vessels, is essential for photoreceptor (PR) function. It recycles vitamin A, which is required for the visual cycle and clears debris generated by the circadian shedding of PR outer segments (1, 2). Each RPE cell phagocytoses and digests the material produced by 30–50 overlying PRs, which shed 10% of their mass daily. The intense and continual phagocytic activity of RPE cells results in the progressive accumulation of indigestible products or “lipofuscin” in their lysosomal compartment (3, 4). Unlike lipofuscins found in other body tissues, which are composed mainly of protein, RPE lipofuscin consists predominantly of lipid-bisretinoids and only 2% protein (5). Lipofuscin bisretinoids (LBs) are vitamin A-derived side products of the visual cycle. Light converts 11-cis-retinal (11CR), the visual pigment chromophore, into all-trans-retinal (ATR), which is immediately flipped by the ATP-binding cassette transporter 4 (Abca4) transporter from the lumen of the outer segment discs to the cytoplasm, where it is reduced to inert all-trans-retinol by retinol dehydrogenase 8 (Rdh8), in mice (6, 7). Small fractions of 11CR and ATR are converted into N-retinylidine-N-ethanolamine (A2E) and other less abundant bisretinoids, which once accumulated in the lysosomes of RPE cells are refractory to all known lysosomal hydrolases (8, 9). The concept that LB accumulation causes retinal degeneration is supported by in vitro and in vivo data that show that excessive LBs are toxic for cultured RPE cells (10, 11), that photoreceptors overlying A2E-laden RPE are more prone to degeneration (12) and that excessive accumulation of LBs in Stargardt’s disease precedes macular degeneration (13). Mice carrying null mutations in Abca4 and Rdh8 develop blindness, basal laminar deposits, and focal accumulations of extracellular debris between the RPE and the Bruch membrane (drusen) (6).Here we report that a family of modified cyclic oligosaccharides, beta cyclodextrins (β-CDs), formed by seven d-glucose units, can encapsulate the hydrophobic arms of A2E within their nonpolar cavity, protect A2E from oxidation, and remove A2E from RPE cells. Our data demonstrate a direct correlation between the ability of β-CDs to perform these protective functions and their affinity for A2E.     

Characterization of the physical development of schoolchildren in different regions of Russia

Age-related changes in some physical development (PD) indices (height, weight, chest circumference, hand dynamometry, and vital capacity) were studied in 21,500 schoolchildren aged 7 to 17 years in 5 federal areas (Central, North-western, Urals, Southern, and Siberian) of the Russian Federation. The moderate development of both morphological and functional characteristics is prevalent in the school-children of all age groups, the proportion of their low development being higher than that of their high development. The proportion of children with average weight is virtually constant in age groups of 7 to 17 years and it is about 50% of the sample. The moderate level of other characteristics is noted for age-related variations of different intensity, which are more pronounced in girls. In terms of age, the functional parameters of PD are more variable than morphological ones. Age-related variation of the ratio of PD levels may be entirely assigned due to: a) heterochronicity of processes of increasing morphological parameters (longitudinal and latitudinal); b) a great variability of functional parameters. Recommendations on correction of schoolchildren's PD with physical educational means are given.