Genetic Mouse Research Articles

Synaptotagmin 1-triggered lipid signaling facilitates coupling of exo- and endocytosis

Exocytosis and endocytosis are essential physiological processes and are of prime importance for brain function. Neurotransmission depends on the Ca2+-triggered exocytosis of synaptic vesicles (SVs). In neurons, exocytosis is spatiotemporally coupled to the retrieval of an equal amount of membrane and SV proteins by compensatory endocytosis. How exocytosis and endocytosis are balanced to maintain presynaptic membrane homeostasis and, thereby, sustain brain function is essentially unknown. We combine mouse genetics with optical imaging to show that the SV calcium sensor Synaptotagmin 1 couples exocytic SV fusion to the endocytic retrieval of SV membranes by promoting the local activity-dependent formation of the signaling lipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) at presynaptic sites. Interference with these mechanisms impairs PI(4,5)P2-triggered SV membrane retrieval but not exocytic SV fusion. Our findings demonstrate that the coupling of SV exocytosis and endocytosis involves local Synaptotagmin 1-induced lipid signaling to maintain presynaptic membrane homeostasis in central nervous system neurons.

The caveats and setbacks of mouse genome editing tools in biomedical studies

Due to the innumerable advantages of using mice as animal models, plenty of strategies to alter mouse genetics have been developed for the purpose of studying the phenotypic outcome of gene mutations. Up until this day, there have been multiple substantial breakthroughs in gene-targeting methods, namely, the utilization of transgene insertion via random integration, gene targeting via homologous recombination, engineered nuclease-mediated targeted mutation, and the Cre-lox approach. Although having facilitated the considerable progress in biomedical research, these techniques are infamously prone to create undesired phenotypes that have been oftentimes mistaken as gene-mutation-related. Hence, being able to identify and avoid these potential artifacts is the most crucial matter in producing transgenic or targeted mutation mouse strains. In this review, we present the fundamentals in generating different mutant mice and the different ways to ensure the credibility of the target gene expression and the observed mutant phenotypes.

Establishment of paternal methylation imprint at the H19/Igf2 imprinting control region.

The insulator model explains the workings of the H19 and Igf2 imprinted domain in the soma, where insulation of the Igf2 promoter from its enhancers occurs by CTCF in the maternally inherited unmethylated chromosome but not the paternally inherited methylated allele. The molecular mechanism that targets paternal methylation imprint establishment to the imprinting control region (ICR) in the male germline is unknown. We tested the function of prospermatogonia-specific broad low-level transcription in this process using mouse genetics. Paternal imprint establishment was abnormal when transcription was stopped at the entry point to the ICR. The germline epimutation persisted into the paternal allele of the soma, resulting in reduced Igf2 in fetal organs and reduced fetal growth, consistent with the insulator model and insulin-like growth factor 2 (IGF2)'s role as fetal growth factor. These results collectively support the role of broad low-level transcription through the H19/Igf2 ICR in the establishment of its paternal methylation imprint in the male germ line, with implications for Silver-Russell syndrome.

Serotonergic dysfunction impairs locomotor coordination in spinal muscular atrophy.

Neuromodulation by serotonin regulates the activity of neuronal networks responsible for a wide variety of essential behaviours. Serotonin (or 5-HT) typically activates metabotropic G protein-coupled receptors, which in turn initiate second messenger signalling cascades and induce short and long-lasting behavioural effects. Serotonin is intricately involved in the production of locomotor activity and gait control for different motor behaviours. Although dysfunction of serotonergic neurotransmission has been associated with mood disorders and spasticity after spinal cord injury, whether and to what extent such dysregulation is implicated in movement disorders has not been firmly established. Here, we investigated whether serotonergic neuromodulation is affected in spinal muscular atrophy (SMA), a neurodegenerative disease caused by ubiquitous deficiency of the SMN protein. The hallmarks of SMA are death of spinal motor neurons, muscle atrophy and impaired motor control, both in human patients and mouse models of disease. We used a severe mouse model of SMA, that closely recapitulates the severe symptoms exhibited by type I SMA patients, the most common and most severe form of the disease. Together, with mouse genetics, optogenetics, physiology, morphology and behavioural analysis, we report severe dysfunction of serotonergic neurotransmission in the spinal cord of SMA mice, both at early and late stages of the disease. This dysfunction is followed by reduction of 5-HT synapses on vulnerable motor neurons. We demonstrate that motor neurons innervating axial and trunk musculature are preferentially affected, suggesting a possible cause for the proximo-distal progression of disease, and raising the possibility that it may underlie scoliosis in SMA patients. We also demonstrate that the 5-HT dysfunction is caused by SMN deficiency in serotonergic neurons in the raphe nuclei of the brainstem. The behavioural significance of the dysfunction in serotonergic neuromodulation is underlined by inter-limb discoordination in SMA mice, which is ameliorated when selective restoration of SMN in 5-HT neurons is achieved by genetic means. Our study uncovers an unexpected dysfunction of serotonergic neuromodulation in SMA and indicates that, if normal function is to be restored under disease conditions, 5-HT neuromodulation should be a key target for therapeutic approaches.

IMMUNOCOMPETENT MICE AS A MODEL FOR PRECLINICAL STUDIES OF mRNA VACCINES IMMUNOGENICITY

Conducting preclinical studies of mRNA vaccines is complicated by the lack of relevant animal models of the human immune system. Immunocompetent mice are widely used in biomedical research. However, critical differences in the genetics and immune system of mice and humans prevent the study of unique human immune responses in mice. Within the framework of this work, the possibility of modeling the cytotoxic T-cell response to mRNA vaccines encoding the S-protein of the SARS-CoV-2 virus was investigated. High-affinity peptides from S-protein were analyzed for the most frequent allelic variants of human MHC-I, two immunocompetent mouse lines (C57BL/6, BALB/c) and an outbred mouse model of IRC. The results of computer modeling have shown that mouse models can be used in preclinical studies of mRNA vaccines against SARS-CoV-2. Mouse MHC-I is able to present virus peptides that are highly affine for human MHC-I. Moreover, the immunogenicity of some of them has already been confirmed by examining blood samples from patients who have had COVID-19.

Autocrine TGF-β-positive feedback in profibrotic AT2-lineage cells plays a crucial role in non-inflammatory lung fibrogenesis

The molecular etiology of idiopathic pulmonary fibrosis (IPF) has been extensively investigated to identify new therapeutic targets. Although anti-inflammatory treatments are not effective for patients with IPF, damaged alveolar epithelial cells play a critical role in lung fibrogenesis. Here, we establish an organoid-based lung fibrosis model using mouse and human lung tissues to assess the direct communication between damaged alveolar type II (AT2)-lineage cells and lung fibroblasts by excluding immune cells. Using this in vitro model and mouse genetics, we demonstrate that bleomycin causes DNA damage and activates p53 signaling in AT2-lineage cells, leading to AT2-to-AT1 transition-like state with a senescence-associated secretory phenotype (SASP). Among SASP-related factors, TGF-β plays an exclusive role in promoting lung fibroblast-to-myofibroblast differentiation. Moreover, the autocrine TGF-β-positive feedback loop in AT2-lineage cells is a critical cellular system in non-inflammatory lung fibrogenesis. These findings provide insights into the mechanism of IPF and potential therapeutic targets.

Tackling Tissue Macrophage Heterogeneity by SplitCre Transgenesis.

Macrophages represent a broad spectrum of distinct, but closely related tissue-resident immune cells. This presents a major challenge for the study of functional aspects of these cells using classical Cre recombinase-mediated conditional mutagenesis in mice, since single promoter-driven Cre transgenic models often display limited specificity toward their intended target. The advent of CRISPR/Cas9 technology has now provided a time- and cost-effective method to explore the full potential of binary transgenic, intersectional genetics. Specifically, the use of two promoters driving inactive Cre fragments that, when co-expressed, dimerize and only then gain recombinase activity allows the characterization and manipulation of genetically defined tissue macrophage subpopulations. Here, we will elaborate on the use of this protocol to capitalize on these recent technological advances in mouse genetics and discuss their strengths and pitfalls to improve the study of tissue macrophage subpopulations in physiology and pathophysiology.

Host genetic variation guides hepacivirus clearance, chronicity, and liver fibrosis in mice.

Human genetic variation is thought to guide the outcome of HCV infection, but model systems within which to dissect these host genetic mechanisms are limited. Norway rat hepacivirus, closely related to HCV, causes chronic liver infection in rats but causes acute self-limiting hepatitis in typical strains of laboratory mice, which resolves in 2 weeks. The Collaborative Cross (CC) is a robust mouse genetics resource comprised of a panel of recombinant inbred strains, which model the complexity of the human genome and provide a system within which to understand diseases driven by complex allelic variation. We infected a panel of CC strains with Norway rat hepacivirus and identified several that failed to clear the virus after 4 weeks. Strains displayed an array of virologic phenotypes ranging from delayed clearance (CC046) to chronicity (CC071, CC080) with viremia for at least 10 months. Body weight loss, hepatocyte infection frequency, viral evolution, T-cell recruitment to the liver, liver inflammation, and the capacity to develop liver fibrosis varied among infected CC strains. These models recapitulate many aspects of HCV infection in humans and demonstrate that host genetic variation affects a multitude of viruses and host phenotypes. These models can be used to better understand the molecular mechanisms that drive hepacivirus clearance and chronicity, the virus and host interactions that promote chronic disease manifestations like liver fibrosis, therapeutic and vaccine performance, and how these factors are affected by host genetic variation.

Genetic and Biological Characterization of H3N2 Avian Influenza Viruses Isolated from Poultry Farms in China between 2019 and 2021

H3N2 influenza viruses not only cause seasonal epidemics in humans but also circulate widely in animals, posing a threat to both animal and human health. Our previous studies indicate that H3N2 avian influenza viruses (AIVs) are readily detected in live poultry markets (LPMs); however, the evolution and biological characteristics of the H3N2 viruses in poultry farms in China are unclear. In this study, we performed active surveillance and collected 49,135 samples from poultry farms. In total, 21 H3N2 AIVs were isolated and their genetics, receptor-binding properties, and replication in mice were evaluated. Phylogenetic analysis indicated that H3N2 AIVs harbor complicated gene constellations and have undergone extensive reassortment; the viruses derived their genes from 12 different hemagglutinin subtypes of duck viruses, including H1, H2, H4, H5, H6, H7, H8, H9, H10, H11, H12, and H14. The complicated gene constellations indicated that H3N2 viruses may have been introduced into poultry farms from different sources, but none have become dominant in poultry farms. Although the H3N2 AIVs possessed avian-type receptor-binding preference, most of the isolates could replicate without preadaptation and some of H3N2 viruses caused weight loss in mice. Notably, two H3N2 viruses acquired the PB2 627K mutation after a single round of replication in mice, suggesting similar mutations could occur if they replicated in humans. Overall, our study demonstrates that the H3N2 AIVs pose a potential threat to the public health and emphasizes the need for continued surveillance of H3N2 viruses in the both LPMs and poultry farms.

Collaborative cross strain CC011/UncJ as a novel mouse model of T2-high, severe asthma

Among asthmatics, there is significant heterogeneity in the clinical presentation and underlying pathophysiological mechanisms, leading to the recognition of multiple disease endotypes (e.g., T2-high vs. T2-low). This heterogeneity extends to severe asthmatics, who may struggle to control symptoms even with high-dose corticosteroid treatment and other therapies. However, there are limited mouse models available to model the spectrum of severe asthma endotypes. We sought to identify a new mouse model of severe asthma by first examining responses to chronic allergen exposure among strains from the Collaborative Cross (CC) mouse genetics reference population, which contains greater genetic diversity than other inbred strain panels previously used for models of asthma. Mice from five CC strains and the often-used classical inbred strain BALB/cJ were chronically exposed to house dust mite (HDM) allergen for five weeks followed by measurements of airway inflammation. CC strain CC011/UncJ (CC011) exhibited extreme responses to HDM including high levels of airway eosinophilia, elevated lung resistance, and extensive airway wall remodeling, and even fatalities among ~ 50% of mice prior to study completion. Compared to BALB/cJ mice, CC011 mice had stronger Th2-mediated airway responses demonstrated by significantly elevated total and HDM-specific IgE and increased Th2 cytokines during tests of antigen recall, but not enhanced ILC2 activation. Airway eosinophilia in CC011 mice was completely dependent upon CD4+ T-cells. Notably, we also found that airway eosinophilia in CC011 mice was resistant to dexamethasone steroid treatment. Thus, the CC011 strain provides a new mouse model of T2-high, severe asthma driven by natural genetic variation likely acting through CD4+ T-cells. Future studies aimed at determining the genetic basis of this phenotype will provide new insights into mechanisms underlying severe asthma.

Synaptic memory and CaMKII: a review.

CaMKII and long-term potentiation (LTP) were discovered within a decade of each other and have been inextricably intertwined ever since. However, like many marriages, it has had its up and downs. Based on the unique biochemical properties of CaMKII, it was proposed as a memory molecule before any direct physiological linkage was made to LTP. This review will assess the state of this marriage 40 years on. How well does the physiological evidence support the role of CaMKII in synaptic memory and what are the remaining outstanding issues?

Excitatory and Inhibitory Descending Commissural Interneurons Differentially Integrate Supraspinal and Segmental Sensory Signals.

The limited information about how descending inputs from the brain and sensory inputs from the periphery use spinal cord interneurons (INs) is a major barrier to understanding how these inputs may contribute to motor functions under normal and pathologic conditions. Commissural interneurons (CINs) are a heterogeneous population of spinal INs that has been implicated in crossed motor responses and bilateral motor coordination (ability to use the right and left side of the body in a coordinated manner) and, therefore, are likely involved in many types of movement (e.g., dynamic posture stabilization, jumping, kicking, walking). In this study, we incorporate mouse genetics, anatomy, electrophysiology, and single-cell calcium imaging to investigate how a subset of CINs, those with descending axons called dCINs, are recruited by descending reticulospinal and segmental sensory signals independently and in combination. We focus on two groups of dCINs set apart by their principal neurotransmitter (glutamate and GABA) and identified as VGluT2+ dCINs and GAD2+ dCINs. We show that VGluT2+ and GAD2+ dCINs are both extensively recruited by reticulospinal and sensory input alone but that VGluT2+ and GAD2+ dCINs integrate these inputs differently. Critically, we find that when recruitment depends on the combined action of reticulospinal and sensory inputs (subthreshold inputs), VGluT2+ dCINs, but not GAD2+ dCINs, are recruited. This difference in the integrative capacity of VGluT2+ and GAD2+ dCINs represents a circuit mechanism that the reticulospinal and segmental sensory systems may avail themselves of to regulate motor behaviors both normally and after injury.SIGNIFICANCE STATEMENT The way supraspinal and peripheral sensory inputs use spinal cord interneurons is fundamental to defining how motor functions are supported both in health and disease. This study, which focuses on dCINs, a heterogeneous population of spinal interneurons critical for crossed motor responses and bilateral motor coordination, shows that both glutamatergic (excitatory) and GABAergic (inhibitory) dCINs can be recruited by supraspinal (reticulospinal) or peripheral sensory inputs. Additionally, the study demonstrates that in conditions where the recruitment of dCINs depends on the combined action of reticulospinal and sensory inputs, only excitatory dCINs are recruited. The study uncovers a circuit mechanism that the reticulospinal and segmental sensory systems may avail themselves of to regulate motor behaviors both normally and after injury.

NR2F1 shapes mitochondria in the mouse brain, providing new insights into Bosch-Boonstra-Schaaf optic atrophy syndrome.

The nuclear receptor NR2F1 acts as a strong transcriptional regulator in embryonic and postnatal neural cells. In humans, mutations in the NR2F1 gene cause Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS), a rare neurodevelopmental disorder characterized by multiple clinical features including vision impairment, intellectual disability and autistic traits. In this study, we identified, by genome-wide and in silico analyses, a set of nuclear-encoded mitochondrial genes as potential genomic targets under direct NR2F1 transcriptional control in neurons. By combining mouse genetic, neuroanatomical and imaging approaches, we demonstrated that conditional NR2F1 loss of function within the adult mouse hippocampal neurogenic niche results in a reduced mitochondrial mass associated with mitochondrial fragmentation and downregulation of key mitochondrial proteins in newborn neurons, the genesis, survival and functional integration of which are impaired. Importantly, we also found dysregulation of several nuclear-encoded mitochondrial genes and downregulation of key mitochondrial proteins in the brain of Nr2f1-heterozygous mice, a validated BBSOAS model. Our data point to an active role for NR2F1 in the mitochondrial gene expression regulatory network in neurons and support the involvement of mitochondrial dysfunction in BBSOAS pathogenesis.

Meiotic Chromosome Structure, the Synaptonemal Complex, and Infertility.

In meiosis, homologous chromosome synapsis is mediated by a supramolecular protein structure, the synaptonemal complex (SC), that assembles between homologous chromosome axes. The mammalian SC comprises at least eight largely coiled-coil proteins that interact and self-assemble to generate a long, zipper-like structure that holds homologous chromosomes in close proximity and promotes the formation of genetic crossovers and accurate meiotic chromosome segregation. In recent years, numerous mutations in human SC genes have been associated with different types of male and female infertility. Here, we integrate structural information on the human SC with mouse and human genetics to describe the molecular mechanisms by which SC mutations can result in human infertility. We outline certain themes in which different SC proteins are susceptible to different types of disease mutation and how genetic variants with seemingly minor effects on SC proteins may act as dominant-negative mutations in which the heterozygous state is pathogenic.

Exploring the interface between the first and second heart fields: Implications for cardiac septation

The embryonic heart elongates by progressive addition of second heart field (SHF) cardiac progenitor cells to the arterial and venous poles of the early heart tube, derived from the first heart field (FHF). The SHF gives rise to the right ventricle, outflow tract and part of the atrial myocardium. SHF-derived parts of the heart are hotspots of congenital heart defects (CHD) and perturbation of SHF deployment underlies a spectrum of CHD. These include atrial and ventricular septal defects that account for over 50% of CHD. Atrial septal structures originate in Tbx1 expressing cells in the posterior dorsal pericardial wall that activate the FHF regulator Tbx5 in response to retinoic acid (RA) signaling. Transient coexpression of Tbx1 and Tbx5 is followed by downregulation of the SHF program, and emergence of a sharp boundary between arterial and venous pole progenitor cells. A similar history of expression of both FHF and SHF regulators, followed by downregulation of the SHF program, demarcates boundary formation at the site of ventricular septation. Here we investigate the cellular and molecular mechanisms of ventricular septum morphogenesis. Using mouse genetics and a conditional dominant negative RA receptor, we show that RA signaling is also required at the heart field interface for morphogenesis of the muscular ventricular septum. Blocking RA signal reception in the SHF results in a bifid ventricular phenotype, identifying a novel RA-dependent zipper phase of ventricular septal morphogenesis. Additionally, blocking RA signal reception in the SHF results in conotruncal CHD. Together, our results point to the importance of RA signaling at the heart field interface for septal morphogenesis, providing new insights into the etiology of CHD.

Endothelial-endothelial signaling as a mechanism for neurovascular coupling

The brain is an energetically expensive organ, consuming 20% of the body’s cardiac output at rest while only accounting for 2% of its mass. Unable to store long-term energy reserves, the brain rapidly redistributes blood flow to active regions in order to meet moment-to-moment changes in metabolic demand. This dynamic process, known as neurovascular coupling, is the basis of most non-invasive human imaging and plays a crucial role in maintaining brain health. However, despite its broad-ranging importance, the cellular mechanisms that underlie neurovascular coupling remain elusive. During neurovascular coupling, activity-evoked signals drive smooth muscle relaxation, resulting in arterial dilation and a robust increase in downstream capillary blood flow. These dilation events occur quickly – on the order of milliseconds – and spread rapidly through the arterial network to effectively recruit perfusion. Electrical signals propagated along the cerebrovascular endothelium are increasingly speculated to underpin this phenomenon, but this idea remains fundamentally untested. Here, we leverage a combination of mouse genetics, molecular biology techniques, and in vivo imaging in awake mice to evaluate the role of propagated electrical signals in the neurovascular coupling response. Our preliminary results indicate that brain endothelial cells are capable of electrical communication and establish a foundation to test the physiological significance of the signals they relay. R01 HL153261/HL/NHLBI NIH HHS/United States; HHMI/Howard Hughes Medical Institute/United States This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Warning regarding hematological toxicity of tamoxifen activated CreERT2 in young Rosa26CreERT2 mice

The Cre-lox system is a versatile and powerful tool used in mouse genetics. It allows spatial and/or temporal control of the deletion of a target gene. The Rosa26-CreERT2 (R26CreERT2) mouse model allows ubiquitous expression of CreERT2. Once activated by tamoxifen, CreERT2 will enter into the nuclei and delete floxed DNA sequences. Here, we show that intraperitoneal injection of tamoxifen in young R26CreERT2 mice leads to morbidity and mortality within 10 days after the first injection, in the absence of a floxed allele. Activation of CreERT2 by tamoxifen led to severe hematological defects, with anemia and a strong disorganization of the bone marrow vascular bed. Cell proliferation was significantly reduced in the bone marrow and the spleen resulting in the depletion of several hematopoietic cells. However, not all cell types or organs were affected to the same extent. We realized that many research groups are not aware of the potential toxicity of Cre recombinases, resulting in misinterpretation of the observed phenotype and in a waste of time and resources. We discuss the necessity to include tamoxifen injected CreERT2 controls lacking a floxed allele in experimental designs and to improve communication about the limitations of Cre-lox mouse models among the scientific community.

Genetic modifiers modulate phenotypic expression of tafazzin deficiency in a mouse model of Barth syndrome.

Barth syndrome is an X-linked disorder caused by loss-of-function mutations in Tafazzin (TAZ), an acyltransferase that catalyzes remodeling of cardiolipin, a signature phospholipid of the inner mitochondrial membrane. Patients develop cardiac and skeletal muscle weakness, growth delay and neutropenia, although phenotypic expression varies considerably between patients. Taz knockout mice recapitulate many of the hallmark features of the disease. We used mouse genetics to test the hypothesis that genetic modifiers alter the phenotypic manifestations of Taz inactivation. We crossed TazKO/X females in the C57BL6/J inbred strain to males from eight inbred strains and evaluated the phenotypes of first-generation (F1) TazKO/Y progeny, compared to TazWT/Y littermates. We observed that genetic background strongly impacted phenotypic expression. C57BL6/J and CAST/EiJ[F1] TazKO/Y mice developed severe cardiomyopathy, whereas A/J[F1] TazKO/Y mice had normal heart function. C57BL6/J and WSB/EiJ[F1] TazKO/Y mice had severely reduced treadmill endurance, whereas endurance was normal in A/J[F1] and CAST/EiJ[F1] TazKO/Y mice. In all genetic backgrounds, cardiolipin showed similar abnormalities in knockout mice, and transcriptomic and metabolomic investigations identified signatures of mitochondrial uncoupling and activation of the integrated stress response. TazKO/Y cardiac mitochondria were small, clustered and had reduced cristae density in knockouts in severely affected genetic backgrounds but were relatively preserved in the permissive A/J[F1] strain. Gene expression and mitophagy measurements were consistent with reduced mitophagy in knockout mice in genetic backgrounds intolerant of Taz mutation. Our data demonstrate that genetic modifiers powerfully modulate phenotypic expression of Taz loss-of-function and act downstream of cardiolipin, possibly by altering mitochondrial quality control.

Deficiency of Group IVA Phospholipase A2 in Collagen-Producing Cells Alleviates the Aggravated Hepatic Fibrosis in High-Fat Diet-Fed Mice after Returning to a Normal Diet.

Hepatic fibrosis, a primary feature of non-alcoholic steatohepatitis (NASH), develops with inflammation and subsequent activation of hepatic stellate cells (HSCs), the main extracellular matrix-producing cells. Currently, no approved pharmacotherapy is available to treat hepatic fibrosis, even under dietary intervention. The activation of cultured HSCs has been shown to be attenuated by pharmacological inhibition of group IVA phospholipase A2 (IVA-PLA2), an enzyme initiating the generation of lipid proinflammatory mediators. We examined the potential utility of IVA-PLA2 of HSCs as a therapeutic target for hepatic fibrosis in NASH under dietary modification using collagen-producing cell-specific IVA-PLA2-conditional knockout mice fed a high-fat diet and then returned to a normal one. Apparent hepatic fibrosis and the accumulation of hepatic lipid droplets developed in the IVA-PLA2-conditional knockout mice on a high-fat diet for nine weeks to a similar degree as in control mice. Most of the lipid droplets disappeared five weeks after switching the diet back to a normal one in both genetic mice. In contrast, the hepatic fibrosis in control mice still progressed even after changing back to a normal diet. However, deficiency of IVA-PLA2 in collagen-producing cells alleviated the aggravated hepatic fibrosis under dietary modification. Our results revealed that the protective effects of an HSC-specific IVA-PLA2 deficiency on fibrogenesis appear after switching the diet from a high-fat one back to a normal one, supporting the promising beneficial effects of the inhibition of IVA-PLA2 on progressive hepatic fibrosis under dietary intervention in NASH treatment.

Magnesium Homeostasis: Lessons from Human Genetics.

Mg 2+ , the fourth most abundant cation in the body, serves as a cofactor for about 600 cellular enzymes. One third of ingested Mg 2+ is absorbed from the gut through a saturable transcellular process and a concentration-dependent paracellular process. Absorbed Mg 2+ is excreted by the kidney and maintains serum Mg 2+ within a narrow range of 0.7-1.25 mmol/L. The reabsorption of Mg 2+ by the nephron is characterized by paracellular transport in the proximal tubule and thick ascending limb. The nature of the transport pathways in the gut epithelia and thick ascending limb has emerged from an understanding of the molecular mechanisms responsible for rare monogenetic disorders presenting with clinical hypomagnesemia. These human disorders due to loss-of-function mutations, in concert with mouse models, have led to a deeper understanding of Mg 2+ transport in the gut and renal tubule. This review focuses on the nature of the transporters and channels revealed by human and mouse genetics and how they are integrated into an understanding of human Mg 2+ physiology.