Mouse forward genetics in the study of the peripheral nervous system and human peripheral neuropathy

Mouse models and strain-dependency of Chédiak-Higashi syndrome-associated neurologic dysfunction

Chédiak-Higashi syndrome (CHS) is a lethal disorder caused by mutations in the LYST gene that involves progressive neurologic dysfunction. Lyst-mutant mice exhibit neurologic phenotypes that are sensitive to genetic background. On the DBA/2J-, but not on the C57BL/6J-background, Lyst-mutant mice exhibit overt tremor phenotypes associated with loss of cerebellar Purkinje cells. Here, we tested whether assays for ataxia could measure this observed strain-dependency, and if so, establish parameters for empowering phenotype- and candidate-driven approaches to identify genetic modifier(s). A composite phenotypic scoring system distinguished phenotypes in Lyst-mutants and uncovered a previously unrecognized background difference between wild-type C57BL/6J and DBA/2J mice. Accelerating rotarod performance also distinguished phenotypes in Lyst-mutants, but at more advanced ages. These results establish that genetic background, Lyst genotype, and age significantly influence the severity of CHS-associated neurologic deficits. Purkinje cell quantifications likewise distinguished phenotypes of Lyst-mutant mice, as well as background differences between wild-type C57BL/6J and DBA/2J mice. To aid identification of potential genetic modifier genes causing these effects, we searched public datasets for cerebellar-expressed genes that are differentially expressed and/or contain potentially detrimental genetic variants. From these approaches, Nos1, Prdx2, Cbln3, Gnb1, Pttg1 were confirmed to be differentially expressed and leading candidates.

GLP‑1R agonists ameliorate peripheral nerve dysfunction and inflammation via p38 MAPK/NF‑κB signaling pathways in streptozotocin‑induced diabetic rats

The present study aimed to investigate the mechanism of glucagon‑like peptide‑1 receptor (GLP‑1R) agonists in the progression of diabetic peripheral neuropathy (DPN) in streptozotocin (STZ)‑induced diabetic rats, through inflammatory signaling pathways. The DPN rat model was generated by intraperitoneal injection of STZ and then treated with the GLP‑1R agonist liraglutide or saline for 8 weeks. These animals were randomly divided into 4 groups (10 rats in each): The normal control + saline group, the normal control + liraglutide group, the diabetic + saline (DM) group and the diabetic + liraglutide (DML) group. The nerve conduction velocity (NCV) in the sciatic nerves of the rats was monitored over a period of 8 weeks. Peripheral serum was obtained for the measurement of blood glucose, tumor necrosis factor‑α (TNF‑α), interleukin‑6 (IL‑6) and IL‑1β level. The protein levels of phosphorylated (p‑) and total extracellular signal‑regulated kinase, c‑Jun NH2‑terminal kinases, p38 mitogen‑activated protein kinases (MAPK), and nuclear and cytoplasmic nuclear factor‑κB (NF‑κB) were measured through western blot analysis. Sciatic nerve mRNA expression levels of proinflammatory chemokines (TNF‑α, IL‑6 and IL‑1β), chemokines [monocyte chemoattractant protein‑1 (MCP‑1)], adhesion molecules [intercellular adhesion molecule 1 (ICAM‑1)], neurotrophic factors [neuritin, nerve growth factor (NGF) and neuron‑specific enolase (NSE)] and NADPH oxidase 4 (NOX4) were evaluated by reverse transcription-quantitative polymerase chain reaction. Subsequent to 8 weeks of treatment with liraglutide, the density of myelin nerve fibers was partially restored in the DML group. The delayed motor NCV and sensory NCV in the DML group were improved. The IOD value of NOX4 staining in the DML group (24.43±9.01) was reduced compared with that in the DM group (56.60±6.91). The levels of TNF‑α, IL‑1β and IL‑6 in the peripheral serum of the DML group were significantly suppressed compared with those of the DM group. It was also observed that the mRNA expression levels of TNF‑α, IL‑6, IL‑1β, MCP‑1, ICAM‑1 and NOX4 in the sciatic nerve were attenuated in the DML group. The mRNA expression of neuritin and NGF was significantly increased in the DML group compared with that of the DM group; NSE was reduced in the sciatic nerves of the DML group compared with that of the DM group. Additionally, the protein expression of p‑p38 MAPK and NF‑κB in the DML group was significantly suppressed. These data demonstrated that GLP‑1R agonists may prevent nerve dysfunction in the sciatic nerves of diabetic rats via p38 MAPK/NF‑κB signaling pathways independent of glycemic control. GLP‑1R agonists may be a useful therapeutic strategy for slowing the progression of DPN.

Genetic modifiers as relevant biological variables of eye disorders

From early in the study of mammalian genetics, it was clear that modifiers can have a striking influence on phenotypes. Today, several modifiers have now been studied in enough detail to allow a glimpse of how they function and influence our perspective of disease. With respect to diseases of the eye, some modifiers are an important source of phenotypic variation that can elucidate how genes function in networks to collectively shape ocular anatomy and physiology, thus influencing our understanding of basic biology. Other modifiers represent an opportunity for new therapeutic targets, whose manipulation could be used to mitigate ophthalmic disease. Here, we review progress in the study of genetic modifiers of eye disorders, with examples from mice and humans that together illustrate the ubiquitous nature of genetic modifiers and why they are relevant biological variables in experimental design. Special emphasis is given to ophthalmic modifiers in mice, especially those relevant to selection of genetic background and those that might inadvertently be a source of experimental variability. These modifiers are capable of influencing interpretations of many experiments using targeted genome manipulations such as knockouts or transgenics. Whereas there are fewer examples of modifiers of eye disorders in humans with a molecular identification, there is ample evidence that they exist and should be considered as a relevant biological variable in human genetic studies as well.

Reduced Proliferation of Oligodendrocyte Progenitor Cells in the Postnatal Brain of Dystonia Musculorum Mice

Dystonia musculorum (dt) mice show sensory neurodegeneration and movement disorder, such as dystonia and cerebellar ataxia. The causative gene Dystonin (Dst) encodes a cytoskeleton linker protein. Although sensory neurodegeneration has been well studied, glial cell responses in the central nervous system (CNS) are poorly understood. Here, we investigated cell proliferation in the CNS of Dst ^Gt homozygous mice using newly generated in situ hybridization (ISH) probes-Ki-67 and proliferating cell nuclear antigen (PCNA) probes-both of which effectively detect proliferating cells. We found that Ki-67-positive cells were significantly decreased in the corpus callosum and thalamus of dt brain at postnatal day 21 (P21). There is a similar but not significant tendency at postnatal day 14 (P14) in the dt brain. We also confirmed the reduced proliferation by PCNA ISH and Ki-67 immunohistochemistry. Double staining with cell-type-specific markers revealed that proliferating cells are oligodendrocyte progenitor cells (OPCs) in both wild-type and dt brain. We also observed a reduced number of Olig2-positive cells in the corpus callosum of Dst ^Gt homozygous mice at P21, indicating that reduced proliferation resulted in a reduced number of OPCs. Our data indicate that OPCs proliferation is reduced in the dt mouse brain at the postnatal stage and that it subsequently results in the reduced number of OPCs.

Remodeling of Mitochondrial Flashes in Muscular Development and Dystrophy in Zebrafish

Mitochondrial flash (mitoflash) is a highly-conserved, universal, and physiological mitochondrial activity in isolated mitochondria, intact cells, and live organisms. Here we investigated developmental and disease-related remodeling of mitoflash activity in zebrafish skeletal muscles. In transgenic zebrafish expressing the mitoflash reporter cpYFP, in vivo imaging revealed that mitoflash frequency and unitary properties underwent multiphasic and muscle type-specific changes, accompanying mitochondrial morphogenesis from 2 to 14 dpf. In particular, short (S)-type mitoflashes predominated in early muscle formation, then S-, transitory (T)- and regular (R)-type mitoflashes coexisted during muscle maturation, followed by a switch to R-type mitoflashes in mature skeletal muscles. In early development of muscular dystrophy, we found accelerated S- to R-type mitoflash transition and reduced mitochondrial NAD(P)H amidst a remarkable cell-to-cell heterogeneity. This study not only unravels a profound functional and morphological remodeling of mitochondria in developing and diseased skeletal muscles, but also underscores mitoflashes as a useful reporter of mitochondrial function in milieu of live animals under physiological and pathophysiological conditions.

Systems genetics of mineral metabolism

Minerals are essential and toxic elements that have an impact on human health. Although we have learned a tremendous amount about the metabolism, biological roles, and health effects of minerals with the tools of biochemistry, cell biology, and molecular genetics, there are gaps in our knowledge of mineral biology that will benefit from new approaches. Forward genetics, whereby variations in phenotypes are mapped to natural genetic variation in the genome, has been successfully used to increase our understanding of many biologically important traits but has not yet been used extensively for mineral metabolism. In addition, the well-appreciated existence of interactions between minerals justifies a broader, systems approach to the study of mineral metabolism, i.e., ionomics. This short review will explain the value of forward genetics and ionomics as tools for exploring mammalian mineral metabolism.

Gene expression of PMP22 is an independent prognostic factor for disease-free and overall survival in breast cancer patients

Background

Gene expression of peripheral myelin protein 22 (PMP22) and the epithelial membrane proteins (EMPs) was found to be differentially expressed in invasive and non-invasive breast cell lines in a previous study. We want to evaluate the prognostic impact of the expression of these genes on breast cancer.

Methods

In a retrospective multicenter study, gene expression of PMP22 and the EMPs was measured in 249 primary breast tumors by real-time PCR. Results were statistically analyzed together with clinical data.

Results

In univariable Cox regression analyses PMP22 and the EMPs were not associated with disease-free survival or tumor-related mortality. However, multivariable Cox regression revealed that patients with higher than median PMP22 gene expression have a 3.47 times higher risk to die of cancer compared to patients with equal values on clinical covariables but lower PMP22 expression. They also have a 1.77 times higher risk to relapse than those with lower PMP22 expression. The proportion of explained variation in overall survival due to PMP22 gene expression was 6.5% and thus PMP22 contributes equally to prognosis of overall survival as nodal status and estrogen receptor status. Cross validation demonstrates that 5-years survival rates can be refined by incorporating PMP22 into the prediction model.

Conclusions

PMP22 gene expression is a novel independent prognostic factor for disease-free survival and overall survival for breast cancer patients. Including it into a model with established prognostic factors will increase the accuracy of prognosis.

A G-coupled receptor protein critical for peripheral nerve myelination

Intercellular signaling between the axon and myelinating glial cells plays an essential role in the regulation of the myelination process. A recent study from Monk et al. has used a forward genetics approach in zebrafish to identify a G protein-coupled receptor that is necessary for Schwann cells to myelinate axons, thereby uncovering a critical component of the axo-glial signaling network.

Concurrent Lpin1 and Nrcam mouse mutations result in severe peripheral neuropathy with transitory hindlimb paralysis

Peripheral neuropathy is a broad category of disorders with a diverse etiology, grouped together by their common pathogenic effect on the peripheral nervous system (PNS). Because of the heterogeneity observed to be responsible for these disorders, a forward genetics method of gene discovery was used to identify additional affected pathways. In this report, we describe the mutant mouse line 20884, generated by N-ethyl-N-nitrosourea mutagenesis, which is characterized by adult-onset transitory hindlimb paralysis. Linkage mapping revealed that two point mutations are responsible for the phenotype: a partial loss-of-function mutation in the gene for phosphatidate phosphatase Lpin1 and a truncation mutation in the gene that encodes the neuronal cell adhesion molecule NrCAM. To investigate how the 20884 Lpin1 and Nrcam mutations interact to produce the paralysis phenotype, the double mutant and both single mutants were analyzed by quantitative behavioral, histological, and electrophysiological means. The Lpin1(20884) mutant and the double mutant are characterized by similar levels of demyelination and aberrant myelin structures. Nevertheless, the double mutant exhibits more severe electrophysiological abnormalities than the Lpin1(20884) mutant. The Nrcam(20884) mutant is characterized by normal sciatic nerve morphology and a mild electrophysiological defect. Comparison of the double mutant phenotype with the two single mutants does not point to an additive relationship between the two defects; rather, the Lpin1(20884) and Nrcam(20884) defects appear to act synergistically to produce the 20884 phenotype. It is proposed that the absence of NrCAM in a demyelinating environment has a deleterious effect, possibly by impairing the process of remyelination.