Mitochondrial hsp60 chaperonopathy causes an autosomal-recessive neurodegenerative disorder linked to brain hypomyelination and leukodystrophy

Hypomyelinating leukodystrophies (HMLs) are disorders involving aberrant myelin formation. The prototype of primary HMLs is the X-linked Pelizaeus-Merzbacher disease (PMD) caused by mutations in PLP1. Recently, homozygous mutations in GJA12 encoding connexin 47 were found in patients with autosomal-recessive Pelizaeus-Merzbacher-like disease (PMLD). However, many patients of both genders with PMLD carry neither PLP1 nor GJA12 mutations. We report a consanguineous Israeli Bedouin kindred with clinical and radiological findings compatible with PMLD, in which linkage to PLP1 and GJA12 was excluded. Using homozygosity mapping and mutation analysis, we have identified a homozygous missense mutation (D29G) not previously described in HSPD1, encoding the mitochondrial heat-shock protein 60 (Hsp60) in all affected individuals. The D29G mutation completely segregates with the disease-associated phenotype. The pathogenic effect of D29G on Hsp60-chaperonin activity was verified by an in vivo E. coli complementation assay, which demonstrated compromised ability of the D29G-Hsp60 mutant protein to support E. coli survival, especially at high temperatures. The disorder, which we have termed MitCHAP-60 disease, can be distinguished from spastic paraplegia 13 (SPG13), another Hsp60-associated autosomal-dominant neurodegenerative disorder, by its autosomal-recessive inheritance pattern, as well as by its early-onset, profound cerebral involvement and lethality. Our findings suggest that Hsp60 defects can cause neurodegenerative pathologies of varying severity, not previously suspected on the basis of the SPG13 phenotype. These findings should help to clarify the important role of Hsp60 in myelinogenesis and neurodegeneration.     

Two faces of chondroitin sulfate proteoglycan in spinal cord repair: a role in microglia/macrophage activation

Background

Chondroitin sulfate proteoglycan (CSPG) is a major component of the glial scar. It is considered to be a major obstacle for central nervous system (CNS) recovery after injury, especially in light of its well-known activity in limiting axonal growth. Therefore, its degradation has become a key therapeutic goal in the field of CNS regeneration. Yet, the abundant de novo synthesis of CSPG in response to CNS injury is puzzling. This apparent dichotomy led us to hypothesize that CSPG plays a beneficial role in the repair process, which might have been previously overlooked because of nonoptimal regulation of its levels. This hypothesis is tested in the present study.

Methods and Findings

We inflicted spinal cord injury in adult mice and examined the effects of CSPG on the recovery process. We used xyloside to inhibit CSPG formation at different time points after the injury and analyzed the phenotype acquired by the microglia/macrophages in the lesion site. To distinguish between the resident microglia and infiltrating monocytes, we used chimeric mice whose bone marrow-derived myeloid cells expressed GFP. We found that CSPG plays a key role during the acute recovery stage after spinal cord injury in mice. Inhibition of CSPG synthesis immediately after injury impaired functional motor recovery and increased tissue loss. Using the chimeric mice we found that the immediate inhibition of CSPG production caused a dramatic effect on the spatial organization of the infiltrating myeloid cells around the lesion site, decreased insulin-like growth factor 1 (IGF-1) production by microglia/macrophages, and increased tumor necrosis factor alpha (TNF-α) levels. In contrast, delayed inhibition, allowing CSPG synthesis during the first 2 d following injury, with subsequent inhibition, improved recovery. Using in vitro studies, we showed that CSPG directly activated microglia/macrophages via the CD44 receptor and modulated neurotrophic factor secretion by these cells.

Conclusions

Our results show that CSPG plays a pivotal role in the repair of injured spinal cord and in the recovery of motor function during the acute phase after the injury; CSPG spatially and temporally controls activity of infiltrating blood-borne monocytes and resident microglia. The distinction made in this study between the beneficial role of CSPG during the acute stage and its deleterious effect at later stages emphasizes the need to retain the endogenous potential of this molecule in repair by controlling its levels at different stages of post-injury repair.     

Order-Based Representation in Random Networks of Cortical Neurons

The wide range of time scales involved in neural excitability and synaptic transmission might lead to ongoing change in the temporal structure of responses to recurring stimulus presentations on a trial-to-trial basis. This is probably the most severe biophysical constraint on putative time-based primitives of stimulus representation in neuronal networks. Here we show that in spontaneously developing large-scale random networks of cortical neurons in vitro the order in which neurons are recruited following each stimulus is a naturally emerging representation primitive that is invariant to significant temporal changes in spike times. With a relatively small number of randomly sampled neurons, the information about stimulus position is fully retrievable from the recruitment order. The effective connectivity that makes order-based representation invariant to time warping is characterized by the existence of stations through which activity is required to pass in order to propagate further into the network. This study uncovers a simple invariant in a noisy biological network in vitro; its applicability under in vivo constraints remains to be seen.     

Unlocking variability: inherent variation and developmental traits of garlic plants originated from sexual reproduction

Recent collections of fertile garlic (Allium sativum) accessions from Central Asia allow a detailed study of seedling developments and the evaluation of inherent variations. We hereby provide a comprehensive account of the ontogenesis of a population of garlic seedlings and their vegetative and reproductive traits. A nucleotide binding site profiling marker technology was applied to provide conclusive evidence for the cross-pollination nature of garlic, and to compare the levels of polymorphism between progeny derived from a single mother clone fertilized by several pollinators. The seedlings’ population demonstrates a large variation in vegetative and reproductive characters, including bulbing ability, bulb color and size, clove number, and response to environmental conditions, similar to that of the genepool of vegetatively propagated garlic clones. In addition, a large variation in flowering and seed production ability was recorded. The understanding of garlic physiology, the availability of the large variability unleashed by sexual reproduction, and the possible utilization of sexual hybridization opens the way for genetic studies and breeding work. Haim D. Rabinowitch and Rina Kamenetsky contributed equally to this paper.     

Mode of action of fenarimol against Leishmania spp

This paper evaluates the effects of certain herbicides on Leishmania spp., their mechanism of action, and the evolutionary origin of the relevant susceptible leishmanial targets. We demonstrated that a relatively nontoxic herbicide, fenarimol, successfully interferes with a leishmanial target, which is probably a relic of an ancient ancestor. Fenarimol impairs the function of leishmanial 14alpha-sterol demethylase, a key enzyme in the sterol biosynthetic pathway. Therefore, fenarimol or its derivatives may be candidates for development of anti-leishmanial drugs. Of the herbicides that have the capability to act as potential inhibitors of the metabolism of Leishmania spp., fenarimol was found as the most active substance against both promastigotes and amastigotes in culture. In addition, it ameliorated lesions caused by Leishmania major in mice. Light microscopy demonstrated rounding of the parasite shape. Increase of osmophilic vacuoles and autophagosomal structures were observed by transmission electron microscopy. Biochemical studies demonstrated that fenarimol inhibited sterol biosynthesis. Docking of fenarimol to the modeled catalytic binding site of 14alpha-lanosterol demethylase of L. major showed a geometrical fit. Fenarimol is stabilized via hydrophobic interactions with the residues that surround it and interactions with the heme ring. These results provide support to the hypothesis that fenarimol inhibits leishmanial sterol biosynthesis. Overall, the findings suggest an additional source of substances for development of anti-leishmanial drugs.     

Neurophysiological studies of flight-related density-dependent phase characteristics in locusts

Locusts show an extreme example of density-dependent phase polymorphism, demonstrating within the species differences in morphology as well as biology, dependent on the population density. Behavior is the primary density-dependent change which facilitates the appearance of various morphological and physiological phase characteristics. We have studied density dependent differences in flight related sensory and central neural elements in the desert locust Schistocerca gregaria. Wind generated high frequency spiking activity in the tritocerebral commissure giant (TCG, an identified interneuron that relay inputs from head hair receptors to thoracic motor centers) that was much less intense in solitary locusts, compared to gregarious ones. In addition the solitary locusts' TCG demonstrated much stronger adaptation of its response. In cases when flight was initiated high frequency TCG activity was independent of the locust phase. The tritocerebral commissure dwarf (TCD) is a GABAergic flight related interneuron that is sensitive to ambient illumination intensity. An increase in the TCD spontaneous activity under dark vs. light conditions was significantly higher in gregarious locusts then in solitary ones, implying a flight-related inhibitory mechanism that is far more active in gregarious locusts under dark conditions. Thus, density-dependent phase differences in interneuron activity pattern and properties well reflect and may be at least partially responsible to behavioral flight-related characteristics.