Haiyang Luo

Manganese transporter Slc39a14 deficiency revealed its key role in maintaining manganese homeostasis in mice

SLC39A14 (also known as ZIP14), a member of the SLC39A transmembrane metal transporter family, has been reported to mediate the cellular uptake of iron and zinc. Recently, however, mutations in the SLC39A14 gene have been linked to manganese (Mn) accumulation in the brain and childhood-onset parkinsonism dystonia. It has therefore been suggested that SLC39A14 deficiency impairs hepatic Mn uptake and biliary excretion, resulting in the accumulation of Mn in the circulation and brain. To test this hypothesis, we generated and characterized global Slc39a14-knockout (Slc39a14−/−) mice and hepatocyte-specific Slc39a14-knockout (Slc39a14fl/fl;Alb-Cre+) mice. Slc39a14−/− mice develop markedly increased Mn concentrations in the brain and several extrahepatic tissues, as well as motor deficits that can be rescued by treatment with the metal chelator Na2CaEDTA. In contrast, Slc39a14fl/fl;Alb-Cre+ mice do not accumulate Mn in the brain or other extrahepatic tissues and do not develop motor deficits, indicating that the loss of Slc39a14 expression selectively in hepatocytes is not sufficient to cause Mn accumulation. Interestingly, Slc39a14fl/fl;Alb-Cre+ mice fed a high Mn diet have increased Mn levels in the serum, brain and pancreas, but not in the liver. Taken together, our results indicate that Slc39a14−/− mice develop brain Mn accumulation and motor deficits that cannot be explained by a loss of Slc39a14 expression in hepatocytes. These findings provide insight into the physiological role that SLC39A14 has in maintaining Mn homeostasis. Our tissue-specific Slc39a14-knockout mouse model can serve as a valuable tool for further dissecting the organ-specific role of SLC39A14 in regulating the body’s susceptibility to Mn toxicity.

Necroptosis in neurodegenerative diseases: a potential therapeutic target

Neurodegenerative diseases are a group of chronic progressive disorders characterized by neuronal loss. Necroptosis, a recently discovered form of programmed cell death, is a cell death mechanism that has necrosis-like morphological characteristics. Necroptosis activation relies on the receptor-interacting protein (RIP) homology interaction motif (RHIM). A variety of RHIM-containing proteins transduce necroptotic signals from the cell trigger to the cell death mediators RIP3 and mixed lineage kinase domain-like protein (MLKL). RIP1 plays a particularly important and complex role in necroptotic cell death regulation ranging from cell death activation to inhibition, and these functions are often cell type and context dependent. Increasing evidence suggests that necroptosis plays an important role in the pathogenesis of neurodegenerative diseases. Moreover, small molecules such as necrostatin-1 are thought inhibit necroptotic signaling pathway. Understanding the precise mechanisms underlying necroptosis and its interactions with other cell death pathways in neurodegenerative diseases could provide significant therapeutic insights. The present review is aimed at summarizing the molecular mechanisms of necroptosis and highlighting the emerging evidence on necroptosis as a major driver of neuron cell death in neurodegenerative diseases.

A novel compound WISP3 mutation in a Chinese family with progressive pseudorheumatoid dysplasia

BACKGROUND Progressive pseudorheumatoid dysplasia (PPD) is an extremely rare autosomal recessive genetic disease caused by mutation of the Wnt1-inducible signaling pathway protein 3 (WISP3) gene. Here, we characterize the clinical manifestations and features of PPD and screen for WISP3 mutations. MATERIALS AND METHODS We performed genetic testing for PPD in a Chinese family, after investigating the clinical particulars and family history, in addition to 200 healthy individuals, who served as the controls for this study. All 5 exons and the exon-intron boundaries of the WISP3 gene were amplified by polymerase chain reaction (PCR) and sequenced directly. RESULTS We identified a missense mutation (c.667T>G, p.C223G) in the maternal allele and a nonsense mutation (c.756C>A, p.C252X) in the paternal allele in the two affected individuals. To our knowledge, the mutation c.756C>A has not been reported previously. In these patients, there was a specific period when their condition markedly improved after having been very serious. Moreover, severe compression of lumbar spinal cord led to conspicuous spinal disorders in the proband. CONCLUSIONS Our study suggests that novel C223G and C252X mutations in exon 4 of the WISP3 gene are responsible for PPD in Chinese patients. Furthermore, we report certain unique phenotypic characteristics in our patients.

MC1R variants in Chinese Han patients with sporadic Parkinson's disease

Recently, a variant p.R160W in the MC1R gene was identified that increased the risk of Parkinsons disease (PD) in Spanish population. To explore whether the MC1R gene variants are associated with sporadic PD in Chinese population, we performed a case-control comparison study for comprehensive MC1R variant screening in 510 Chinese Han patients and 495 healthy controls as ethnically matched controls. We identify 5 nonsynonymous variants, including rs34090186 (p.R67Q), rs2228479 (p.V92M), rs33932559 (p.I120T), rs885479 (p.R163Q), and rs372152373 (p.R223W). However, variants mentioned previously did not show association with PD. Our results suggest that variants in MC1R do not play a major role in PD in the Chinese population.

Recessive hereditary motor and sensory neuropathy caused by IGHMBP2 gene mutation

Hereditary motor and sensory neuropathy (HMSN), also known as Charcot-Marie-Tooth disease (CMT), is a genetically heterogeneous disorder that affects both sensory and motor peripheral nerves. HMSN is characterized by distal and symmetric muscle atrophy in the lower limbs and hands, foot abnormalities, and distal sensory loss. It is associated with more than 50 causative genes or loci; however, the genetic cause remains undetermined in almost 50% of HMSN cases.1,2

Exome sequencing reveals novel SPG11 mutation in hereditary spastic paraplegia with complicated phenotypes

We used a combined approach of whole-exome sequencing and candidate mutation validation to identify the disease-causing gene in a hereditary spastic paraplegia (HSP) patient with lower motor neuron involvement, mild cerebellar signs and dysgenesis of the corpus callosum. HSP is a clinically and genetically heterogeneous neurodegenerative disorder characterized by degeneration of the corticospinal tract motor neurons and resulting in progressive lower limb spasticity, often with a complicated phenotype. We identified novel compound heterozygous mutations in the SPG11 gene in this patient as follows: a mutation in exon 32, c.6194C > G transition (p.S2056X) and a novel c.5121+1C > T splicing mutation. Our finding suggests that these novel compound heterozygous mutations in SPG11 are associated with HSP and lower motor neuron involvement, mild cerebellar signs and dysgenesis of the corpus callosum. This study also demonstrates that exome sequencing is an efficient and rapid diagnostic tool for identifying the causes of some complex and genetically heterogeneous neurodegenerative diseases.

Disrupted structure and aberrant function of CHIP mediates the loss of motor and cognitive function in preclinical models of SCAR16

CHIP (carboxyl terminus of heat shock 70-interacting protein) has long been recognized as an active member of the cellular protein quality control system given the ability of CHIP to function as both a co-chaperone and ubiquitin ligase. We discovered a genetic disease, now known as spinocerebellar autosomal recessive 16 (SCAR16), resulting from a coding mutation that caused a loss of CHIP ubiquitin ligase function. The initial mutation describing SCAR16 was a missense mutation in the ubiquitin ligase domain of CHIP (p.T246M). Using multiple biophysical and cellular approaches, we demonstrated that T246M mutation results in structural disorganization and misfolding of the CHIP U-box domain, promoting oligomerization, and increased proteasome-dependent turnover. CHIP-T246M has no ligase activity, but maintains interactions with chaperones and chaperone-related functions. To establish preclinical models of SCAR16, we engineered T246M at the endogenous locus in both mice and rats. Animals homozygous for T246M had both cognitive and motor cerebellar dysfunction distinct from those observed in the CHIP null animal model, as well as deficits in learning and memory, reflective of the cognitive deficits reported in SCAR16 patients. We conclude that the T246M mutation is not equivalent to the total loss of CHIP, supporting the concept that disease-causing CHIP mutations have different biophysical and functional repercussions on CHIP function that may directly correlate to the spectrum of clinical phenotypes observed in SCAR16 patients. Our findings both further expand our basic understanding of CHIP biology and provide meaningful mechanistic insight underlying the molecular drivers of SCAR16 disease pathology, which may be used to inform the development of novel therapeutics for this devastating disease.

CHCHD10 is involved in the development of Parkinson’s disease caused by CHCHD2 loss-of-function mutation p.T61I

Previously we identified the p.Thr61Ile mutation in coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2) in a Chinese family with autosomal dominant Parkinsons disease. But the mechanism is still unclear. In this study, we explored the effects of CHCHD2 p.Thr61Ile mutation in cells and its association with coiled-coil-helix-coiled-coil-helix domain containing 10 (CHCHD10). We found that overexpression of Parkinsons disease-associated T61I mutant CHCHD2 did not produce mitochondrial dysfunction. Rather, its protective effect from stress was abrogated. And, the level of the CHCHD2 protein and mRNA in patient fibroblasts was not significantly different from control. In addition, CHCHD2 T61I mutation caused increased interaction with CHCHD10 and reduced CHCHD10 level. The mitochondrial ultrastructural alterations in CHCHD2 T61I mutant patient fibroblasts are similar to that of CHCHD10 mutations. We therefore propose that CHCHD10 is involved in the development of Parkinsons disease caused by CHCHD2 loss-of-function mutation p.T61I.

Arginine vasopressin relates with spatial learning and memory in a mouse model of spinocerebellar ataxia type 3

Spinocerebellar ataxia is an inherited neurodegenerative disorder that the most prevalent type is type 3 (SCA3). Arginine vasopressin (AVP) is released within the lateral septum for controlling the learning and memory. This communication studied the effect of AVP on the spatial learning and memory of SCA3 mice. The spatial learning and memory were analyzed by Morris water maze test (MWM), and AVP concentration was measured by radioimmunoassay. The results showed that (Alves et al., 2010) the swimming velocity, distance traveled and latency to the platform of MWM in SCA3 mice were reduced slower than those in WT mice over 4 training days (p<0.05, 0.01 or 0.001); (Antunes and Zimmerman, 1978) SCA3 mice showed a lower performance of spatial learning and memory of MWM during the fifth day (test day) compared to WT mice; (Bao et al., 2014) SCA3 mice had a decrease of AVP concentration in cerebral cortex (6.3±0.6pg/mg vs. 11.4±1.0pg/mg, p<0.01), hypothalamus (6.1±1.3ng/mg vs. 10.3±2.1ng/mg, p<0.05), hippocampus (3.2±0.5pg/mg vs. 5.2±1.0pg/mg, p<0.01) and cerebellum (4.7±0.9pg/mg vs. 8.3±1.1pg/mg, p<0.01), not in spinal cord, pituitary and serum; and (Barberies and Tribollet, 1996) intraventricular AVP could significantly quicken swimming velocity, cut down distance traveled and reduce latency to the platform of MWM in a dose-dependent manner, but intraventricular AVP receptor antagonist weakened the spatial learning and memory of MWM in SCA3 mice during the fifth day. The data suggested that AVP in the brain, not spinal cord and peripheral system of SCA3 mice related with the change of the spatial learning and memory of MWM.

CADASIL mutant NOTCH3(R90C) decreases the viability of HS683 oligodendrocytes via apoptosis

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common hereditary cerebral small vessel disease caused by mutations in NOTCH3. Prevailing models suggest that demyelination occurs secondary to vascular pathology. However, in zebrafish, NOTCH3 is also expressed in mature oligodendrocytes. Thus, we hypothesized that in addition to vascular defects, mutant NOTCH3 may alter glial function in individuals with CADASIL. The aim of this study was to characterize the direct effects of a mutant NOTCH3 protein in HS683 oligodendrocytes. HS683 oligodendrocytes transfected with wild-type NOTCH3, mutant NOTCH3(R90C), and empty control vector were used to study the impact of the NOTCH3(R90C) mutant on its protein hydrolytic processing, cell viability, apoptosis, autophagy, oxidative stress, and the related upstream events using immunoblotting, immunofluorescence, RT-PCR, and flow cytometry. We determined that HS683 oligodendrocytes transfected with mutant NOTCH3(R90C), which is the hotspot mutation site-associated with CADASIL, exhibited aberrant NOTCH3 proteolytic processing. Compared to cells overexpressing wild-type NOTCH3, cells overexpressing NOTCH3(R90C) were less viable and had a higher rate of apoptosis. Immunoblotting revealed that cells transfected with NOTCH3(R90C) had higher levels of intrinsic mitochondrial apoptosis, extrinsic death receptor path-related apoptosis, and autophagy compared with cells transfected with wild-type NOTCH3. This study suggests that in patients with CADASIL, early defects in glia influenced by NOTCH3(R90C) may directly contribute to white matter pathology in addition to secondary vascular defects. This study provides a potential therapeutic target for the future treatment of CADASIL.