Proper development of the CNS axon-glia unit requires bi-directional communication between axons ... more Proper development of the CNS axon-glia unit requires bi-directional communication between axons and oligodendrocytes (OLs). We show that the signaling lipid phosphatidylinositol-3,5-bisphosphate [PI(3,5)P2] is required in neurons and in OLs for normal CNS myelination. In mice, mutations of Fig4, Pikfyve or Vac14, encoding key components of the PI(3,5)P2 biosynthetic complex, each lead to impaired OL maturation, severe CNS hypomyelination and delayed propagation of compound action potentials. Primary OLs deficient in Fig4 accumulate large LAMP1(+) and Rab7(+) vesicular structures and exhibit reduced membrane sheet expansion. PI(3,5)P2 deficiency leads to accumulation of myelin-associated glycoprotein (MAG) in LAMP1(+) perinuclear vesicles that fail to migrate to the nascent myelin sheet. Live-cell imaging of OLs after genetic or pharmacological inhibition of PI(3,5)P2 synthesis revealed impaired trafficking of plasma membrane-derived MAG through the endolysosomal system in primary cells and brain tissue. Collectively, our studies identify PI(3,5)P2 as a key regulator of myelin membrane trafficking and myelinogenesis.
The lipid phosphatase FIG4 is a subunit of the protein complex that regulates biosynthesis of the... more The lipid phosphatase FIG4 is a subunit of the protein complex that regulates biosynthesis of the signaling lipid PI(3,5)P2. Mutations of FIG4 result in juvenile lethality and spongiform neurodegeneration in the mouse, and are responsible for the human disorders Charcot-Marie-Tooth Disease, Yunis-Varon Syndrome and polymicrogyria with seizures. We previously demonstrated that conditional expression of a wildtype FIG4 transgene in neurons is sufficient to rescue most of the abnormalities of Fig4 null mice, including juvenile lethality and extensive neurodegeneration. To evaluate the contribution of the phosphatase activity to the in vivo function of Fig4, we introduced the mutation p.Cys486Ser into the Sac phosphatase active site motif CX5RT. Transfection of the Fig4(Cys486Ser) cDNA into cultured Fig4(-/-) fibroblasts was effective in preventing vacuolization. Neuronal expression of an NSE- Fig4(Cys486Ser) transgene in vivo prevented the neonatal neurodegeneration and juvenile lethal...
Summary An estimated 1-2% of the general population harbor abdominal aortic aneurysms (AAAs) with... more Summary An estimated 1-2% of the general population harbor abdominal aortic aneurysms (AAAs) with up to a 10% prevalence in older age groups. Rupture of AAAs is one of the leading causes of death in industrialized countries with aging populations. For example, ...
Abdominal aortic aneurysms (AAAs) are a complex disease with a late age at onset. Causing approxi... more Abdominal aortic aneurysms (AAAs) are a complex disease with a late age at onset. Causing approximately 15,000 deaths per year, AAAs are among the top twenty leading causes of death in the United States. A main reason for the high mortality rate of AAAs is that most are asymptomatic until rupture. Local inflammation of the aorta, fragmentation of the extracellular matrix and loss of smooth muscle cells are distinct characteristics of AAA formation. Large epidemiological studies have shown that smoking and positive family history are the two most important risk factors for AAAs. Other risk factors include male sex, increasing age, hypertension and high cholesterol. Interestingly, diabetes has a negative association with AAA. A genome-wide approach using DNA linkage analysis has found susceptibility loci for AAAs on chromosomes 19q13 and 4q31 and a genetic association study identified a variant on chromosome 9p21 associated with AAA in addition to other vascular phenotypes. Microarray...
ABSTRACT Abdominal aortic aneurysm (AAA) is a multifactorial disease with a significant genetic c... more ABSTRACT Abdominal aortic aneurysm (AAA) is a multifactorial disease with a significant genetic component. Epidemiological studies have identified family history of AAA as a risk factor for both aneurysm development and rupture, making it an important consideration for targeted ultrasound screening of elderly patients and their family members. Ongoing research into the genetics of AAA is focused on identifying risk factor genes for both familial and sporadic aneurysms through the use of linkage analyses and genetic association studies, although no causative mutations have yet been identified. Additionally, micro-array expression profiling and animal models of aneurysms are being used to identify genes and pathways for the design of novel therapeutics. These approaches promise to deliver a better understanding of aneurysms at the molecular level leading to improved screening and treatment. KeywordsDNAlinkage-Geneticassociation-Chromosome19-Chromosome4-Animal models-Family studies-Ultrasonography screening-Microarray
Frequently candidate regions from linkage analyses contain several hundreds of genes. An approach... more Frequently candidate regions from linkage analyses contain several hundreds of genes. An approach to reduce the list of positional candidate genes is to use gene expression data from diseased and healthy tissue. Genes that are not expressed, either in diseased or healthy tissue, may be excluded from the candidate list. Here we used this approach to assist in the identification of candidate genes for the complex disease intracranial aneurysm (IA). IAs may grow, rupture, and lead to subarachnoid hemorrhage. Each year about 30,000 individuals in the United States suffer ruptured IA. Despite evidence for a genetic predisposition for IA and previously reported linkage, including to chromosome 19q13, specific genes that contribute to IA have yet to be identified. Methods: Intracranial arteries from individuals with IA were obtained postmortem and pooled (n=4) into sample sets to represent aneurysmal intracranial arteries and healthy contralateral vessels (controls) obtained from the same ...
Abdominal aortic aneurysm (AAA) is a complex multifactorial disease with life-threatening implica... more Abdominal aortic aneurysm (AAA) is a complex multifactorial disease with life-threatening implications. Aneurysms typically have no signs or symptoms, and rupture of AAA has a high mortality rate. Multiple environmental and genetic risk factors are involved in aneurysm formation and progression making it a complicated disease to study. Little is understood about the mechanisms in disease initiation, thus there are currently no therapeutic approaches to prevent AAA, leaving patients with surgery as their only option. Ongoing research into the genetic components of AAA using a candidate gene approach has been overall unsuccessful. A more promising approach to study complex diseases involves genome-wide techniques such as DNA linkage analysis, genetic association studies and microarray expression profiling. Furthermore, studies involving inhibition of AAA progression, rather than formation, have a potentially promising outcome. Targeting biological pathways in AAA pathogenesis may bene...
Mutations of FIG4 are responsible for Yunis-Varón syndrome, familial epilepsy with polymicrogyria... more Mutations of FIG4 are responsible for Yunis-Varón syndrome, familial epilepsy with polymicrogyria, and Charcot-Marie-Tooth type 4J neuropathy (CMT4J). Although loss of the FIG4 phospholipid phosphatase consistently causes decreased PtdIns(3,5)P2 levels, cell-specific sensitivity to partial loss of FIG4 function may differentiate FIG4-associated disorders. CMT4J is an autosomal recessive neuropathy characterized by severe demyelination and axonal loss in human, with both motor and sensory involvement. However, it is unclear whether FIG4 has cell autonomous roles in both motor neurons and Schwann cells, and how loss of FIG4/PtdIns(3,5)P2-mediated functions contribute to the pathogenesis of CMT4J. Here, we report that mice with conditional inactivation of Fig4 in motor neurons display neuronal and axonal degeneration. In contrast, conditional inactivation of Fig4 in Schwann cells causes demyelination and defects in autophagy-mediated degradation. Moreover, Fig4-regulated endolysosomal ...
Recently, two common sequence variants on 9p21, tagged by rs10757278-G and rs10811661-T, were rep... more Recently, two common sequence variants on 9p21, tagged by rs10757278-G and rs10811661-T, were reported to be associated with coronary artery disease (CAD) and type 2 diabetes (T2D), respectively. We proceeded to further investigate the contributions of these variants to arterial diseases and T2D. Here we report that rs10757278-G is associated with, in addition to CAD, abdominal aortic aneurysm (AAA; odds ratio (OR) = 1.31, P = 1.2 x 10(-12)) and intracranial aneurysm (OR = 1.29, P = 2.5 x 10(-6)), but not with T2D. This variant is the first to be described that affects the risk of AAA and intracranial aneurysm in many populations. The association of rs10811661-T to T2D replicates in our samples, but the variant does not associate with any of the five arterial diseases examined. These findings extend our insight into the role of the sequence variant tagged by rs10757278-G and show that it is not confined to atherosclerotic diseases.
FIG4 is a ubiquitously expressed phosphatase that, in complex with FAB1/PIKFYVE and VAC14, regula... more FIG4 is a ubiquitously expressed phosphatase that, in complex with FAB1/PIKFYVE and VAC14, regulates the biosynthesis of the signaling lipid PI(3,5)P(2). Null mutation of Fig4 in the mouse results in spongiform degeneration of brain and peripheral ganglia, defective myelination and juvenile lethality. Partial loss-of-function of human FIG4 results in a severe form of Charcot-Marie-Tooth neuropathy. Neurons from null mice contain enlarged vacuoles derived from the endosome/lysosome pathway, and astrocytes accumulate proteins involved in autophagy. Other cellular defects include astrogliosis and microgliosis. To distinguish the contributions of neurons and glia to spongiform degeneration in the Fig4 null mouse, we expressed Fig4 under the control of the neuron-specific enolase promoter and the astrocyte-specific glial fibrillary acidic protein promoter in transgenic mice. Neuronal expression of Fig4 was sufficient to rescue cellular and neurological phenotypes including spongiform degeneration, gliosis and juvenile lethality. In contrast, expression of Fig4 in astrocytes prevented accumulation of autophagy markers and microgliosis but did not prevent spongiform degeneration or lethality. To confirm the neuronal origin of spongiform degeneration, we generated a floxed allele of Fig4 and crossed it with mice expressing the Cre recombinase from the neuron-specific synapsin promoter. Mice with conditional inactivation of Fig4 in neurons developed spongiform degeneration and the full spectrum of neurological abnormalities. The data demonstrate that expression of Fig4 in neurons is necessary and sufficient to prevent spongiform degeneration. Therapy for patients with FIG4 deficiency will therefore require correction of the deficiency in neurons.
Pre-eclampsia (PE) affects 5-7% of pregnancies in the US, and is a leading cause of maternal deat... more Pre-eclampsia (PE) affects 5-7% of pregnancies in the US, and is a leading cause of maternal death and perinatal morbidity and mortality worldwide. To identify genes with a role in PE, we conducted a large-scale association study evaluating 775 SNPs in 190 candidate genes selected for a potential role in obstetrical complications. SNP discovery was performed by DNA sequencing, and genotyping was carried out in a high-throughput facility using the MassARRAY(TM) System. Women with PE (n = 394) and their offspring (n = 324) were compared with control women (n = 602) and their offspring (n = 631) from the same hospital-based population. Haplotypes were estimated for each gene using the EM algorithm, and empirical p values were obtained for a logistic regression-based score test, adjusted for significant covariates. An interaction model between maternal and offspring genotypes was also evaluated. The most significant findings for association with PE were COL1A1 (p = 0.0011) and IL1A (p = 0.0014) for the maternal genotype, and PLAUR (p = 0.0008) for the offspring genotype. Common candidate genes for PE, including MTHFR and NOS3, were not significantly associated with PE. For the interaction model, SNPs within IGF1 (p = 0.0035) and IL4R (p = 0.0036) gave the most significant results. This study is one of the most comprehensive genetic association studies of PE to date, including an evaluation of offspring genotypes that have rarely been considered in previous studies. Although we did not identify statistically significant evidence of association for any of the candidate loci evaluated here after adjusting for multiple testing using the false discovery rate, additional compelling evidence exists, including multiple SNPs with nominally significant p values in COL1A1 and the IL1A region, and previous reports of association for IL1A, to support continued interest in these genes as candidates for PE. Identification of the genetic regulators of PE may have broader implications, since women with PE are at increased risk of death from cardiovascular diseases later in life.
Proper development of the CNS axon-glia unit requires bi-directional communication between axons ... more Proper development of the CNS axon-glia unit requires bi-directional communication between axons and oligodendrocytes (OLs). We show that the signaling lipid phosphatidylinositol-3,5-bisphosphate [PI(3,5)P2] is required in neurons and in OLs for normal CNS myelination. In mice, mutations of Fig4, Pikfyve or Vac14, encoding key components of the PI(3,5)P2 biosynthetic complex, each lead to impaired OL maturation, severe CNS hypomyelination and delayed propagation of compound action potentials. Primary OLs deficient in Fig4 accumulate large LAMP1(+) and Rab7(+) vesicular structures and exhibit reduced membrane sheet expansion. PI(3,5)P2 deficiency leads to accumulation of myelin-associated glycoprotein (MAG) in LAMP1(+) perinuclear vesicles that fail to migrate to the nascent myelin sheet. Live-cell imaging of OLs after genetic or pharmacological inhibition of PI(3,5)P2 synthesis revealed impaired trafficking of plasma membrane-derived MAG through the endolysosomal system in primary cells and brain tissue. Collectively, our studies identify PI(3,5)P2 as a key regulator of myelin membrane trafficking and myelinogenesis.
The lipid phosphatase FIG4 is a subunit of the protein complex that regulates biosynthesis of the... more The lipid phosphatase FIG4 is a subunit of the protein complex that regulates biosynthesis of the signaling lipid PI(3,5)P2. Mutations of FIG4 result in juvenile lethality and spongiform neurodegeneration in the mouse, and are responsible for the human disorders Charcot-Marie-Tooth Disease, Yunis-Varon Syndrome and polymicrogyria with seizures. We previously demonstrated that conditional expression of a wildtype FIG4 transgene in neurons is sufficient to rescue most of the abnormalities of Fig4 null mice, including juvenile lethality and extensive neurodegeneration. To evaluate the contribution of the phosphatase activity to the in vivo function of Fig4, we introduced the mutation p.Cys486Ser into the Sac phosphatase active site motif CX5RT. Transfection of the Fig4(Cys486Ser) cDNA into cultured Fig4(-/-) fibroblasts was effective in preventing vacuolization. Neuronal expression of an NSE- Fig4(Cys486Ser) transgene in vivo prevented the neonatal neurodegeneration and juvenile lethal...
Summary An estimated 1-2% of the general population harbor abdominal aortic aneurysms (AAAs) with... more Summary An estimated 1-2% of the general population harbor abdominal aortic aneurysms (AAAs) with up to a 10% prevalence in older age groups. Rupture of AAAs is one of the leading causes of death in industrialized countries with aging populations. For example, ...
Abdominal aortic aneurysms (AAAs) are a complex disease with a late age at onset. Causing approxi... more Abdominal aortic aneurysms (AAAs) are a complex disease with a late age at onset. Causing approximately 15,000 deaths per year, AAAs are among the top twenty leading causes of death in the United States. A main reason for the high mortality rate of AAAs is that most are asymptomatic until rupture. Local inflammation of the aorta, fragmentation of the extracellular matrix and loss of smooth muscle cells are distinct characteristics of AAA formation. Large epidemiological studies have shown that smoking and positive family history are the two most important risk factors for AAAs. Other risk factors include male sex, increasing age, hypertension and high cholesterol. Interestingly, diabetes has a negative association with AAA. A genome-wide approach using DNA linkage analysis has found susceptibility loci for AAAs on chromosomes 19q13 and 4q31 and a genetic association study identified a variant on chromosome 9p21 associated with AAA in addition to other vascular phenotypes. Microarray...
ABSTRACT Abdominal aortic aneurysm (AAA) is a multifactorial disease with a significant genetic c... more ABSTRACT Abdominal aortic aneurysm (AAA) is a multifactorial disease with a significant genetic component. Epidemiological studies have identified family history of AAA as a risk factor for both aneurysm development and rupture, making it an important consideration for targeted ultrasound screening of elderly patients and their family members. Ongoing research into the genetics of AAA is focused on identifying risk factor genes for both familial and sporadic aneurysms through the use of linkage analyses and genetic association studies, although no causative mutations have yet been identified. Additionally, micro-array expression profiling and animal models of aneurysms are being used to identify genes and pathways for the design of novel therapeutics. These approaches promise to deliver a better understanding of aneurysms at the molecular level leading to improved screening and treatment. KeywordsDNAlinkage-Geneticassociation-Chromosome19-Chromosome4-Animal models-Family studies-Ultrasonography screening-Microarray
Frequently candidate regions from linkage analyses contain several hundreds of genes. An approach... more Frequently candidate regions from linkage analyses contain several hundreds of genes. An approach to reduce the list of positional candidate genes is to use gene expression data from diseased and healthy tissue. Genes that are not expressed, either in diseased or healthy tissue, may be excluded from the candidate list. Here we used this approach to assist in the identification of candidate genes for the complex disease intracranial aneurysm (IA). IAs may grow, rupture, and lead to subarachnoid hemorrhage. Each year about 30,000 individuals in the United States suffer ruptured IA. Despite evidence for a genetic predisposition for IA and previously reported linkage, including to chromosome 19q13, specific genes that contribute to IA have yet to be identified. Methods: Intracranial arteries from individuals with IA were obtained postmortem and pooled (n=4) into sample sets to represent aneurysmal intracranial arteries and healthy contralateral vessels (controls) obtained from the same ...
Abdominal aortic aneurysm (AAA) is a complex multifactorial disease with life-threatening implica... more Abdominal aortic aneurysm (AAA) is a complex multifactorial disease with life-threatening implications. Aneurysms typically have no signs or symptoms, and rupture of AAA has a high mortality rate. Multiple environmental and genetic risk factors are involved in aneurysm formation and progression making it a complicated disease to study. Little is understood about the mechanisms in disease initiation, thus there are currently no therapeutic approaches to prevent AAA, leaving patients with surgery as their only option. Ongoing research into the genetic components of AAA using a candidate gene approach has been overall unsuccessful. A more promising approach to study complex diseases involves genome-wide techniques such as DNA linkage analysis, genetic association studies and microarray expression profiling. Furthermore, studies involving inhibition of AAA progression, rather than formation, have a potentially promising outcome. Targeting biological pathways in AAA pathogenesis may bene...
Mutations of FIG4 are responsible for Yunis-Varón syndrome, familial epilepsy with polymicrogyria... more Mutations of FIG4 are responsible for Yunis-Varón syndrome, familial epilepsy with polymicrogyria, and Charcot-Marie-Tooth type 4J neuropathy (CMT4J). Although loss of the FIG4 phospholipid phosphatase consistently causes decreased PtdIns(3,5)P2 levels, cell-specific sensitivity to partial loss of FIG4 function may differentiate FIG4-associated disorders. CMT4J is an autosomal recessive neuropathy characterized by severe demyelination and axonal loss in human, with both motor and sensory involvement. However, it is unclear whether FIG4 has cell autonomous roles in both motor neurons and Schwann cells, and how loss of FIG4/PtdIns(3,5)P2-mediated functions contribute to the pathogenesis of CMT4J. Here, we report that mice with conditional inactivation of Fig4 in motor neurons display neuronal and axonal degeneration. In contrast, conditional inactivation of Fig4 in Schwann cells causes demyelination and defects in autophagy-mediated degradation. Moreover, Fig4-regulated endolysosomal ...
Recently, two common sequence variants on 9p21, tagged by rs10757278-G and rs10811661-T, were rep... more Recently, two common sequence variants on 9p21, tagged by rs10757278-G and rs10811661-T, were reported to be associated with coronary artery disease (CAD) and type 2 diabetes (T2D), respectively. We proceeded to further investigate the contributions of these variants to arterial diseases and T2D. Here we report that rs10757278-G is associated with, in addition to CAD, abdominal aortic aneurysm (AAA; odds ratio (OR) = 1.31, P = 1.2 x 10(-12)) and intracranial aneurysm (OR = 1.29, P = 2.5 x 10(-6)), but not with T2D. This variant is the first to be described that affects the risk of AAA and intracranial aneurysm in many populations. The association of rs10811661-T to T2D replicates in our samples, but the variant does not associate with any of the five arterial diseases examined. These findings extend our insight into the role of the sequence variant tagged by rs10757278-G and show that it is not confined to atherosclerotic diseases.
FIG4 is a ubiquitously expressed phosphatase that, in complex with FAB1/PIKFYVE and VAC14, regula... more FIG4 is a ubiquitously expressed phosphatase that, in complex with FAB1/PIKFYVE and VAC14, regulates the biosynthesis of the signaling lipid PI(3,5)P(2). Null mutation of Fig4 in the mouse results in spongiform degeneration of brain and peripheral ganglia, defective myelination and juvenile lethality. Partial loss-of-function of human FIG4 results in a severe form of Charcot-Marie-Tooth neuropathy. Neurons from null mice contain enlarged vacuoles derived from the endosome/lysosome pathway, and astrocytes accumulate proteins involved in autophagy. Other cellular defects include astrogliosis and microgliosis. To distinguish the contributions of neurons and glia to spongiform degeneration in the Fig4 null mouse, we expressed Fig4 under the control of the neuron-specific enolase promoter and the astrocyte-specific glial fibrillary acidic protein promoter in transgenic mice. Neuronal expression of Fig4 was sufficient to rescue cellular and neurological phenotypes including spongiform degeneration, gliosis and juvenile lethality. In contrast, expression of Fig4 in astrocytes prevented accumulation of autophagy markers and microgliosis but did not prevent spongiform degeneration or lethality. To confirm the neuronal origin of spongiform degeneration, we generated a floxed allele of Fig4 and crossed it with mice expressing the Cre recombinase from the neuron-specific synapsin promoter. Mice with conditional inactivation of Fig4 in neurons developed spongiform degeneration and the full spectrum of neurological abnormalities. The data demonstrate that expression of Fig4 in neurons is necessary and sufficient to prevent spongiform degeneration. Therapy for patients with FIG4 deficiency will therefore require correction of the deficiency in neurons.
Pre-eclampsia (PE) affects 5-7% of pregnancies in the US, and is a leading cause of maternal deat... more Pre-eclampsia (PE) affects 5-7% of pregnancies in the US, and is a leading cause of maternal death and perinatal morbidity and mortality worldwide. To identify genes with a role in PE, we conducted a large-scale association study evaluating 775 SNPs in 190 candidate genes selected for a potential role in obstetrical complications. SNP discovery was performed by DNA sequencing, and genotyping was carried out in a high-throughput facility using the MassARRAY(TM) System. Women with PE (n = 394) and their offspring (n = 324) were compared with control women (n = 602) and their offspring (n = 631) from the same hospital-based population. Haplotypes were estimated for each gene using the EM algorithm, and empirical p values were obtained for a logistic regression-based score test, adjusted for significant covariates. An interaction model between maternal and offspring genotypes was also evaluated. The most significant findings for association with PE were COL1A1 (p = 0.0011) and IL1A (p = 0.0014) for the maternal genotype, and PLAUR (p = 0.0008) for the offspring genotype. Common candidate genes for PE, including MTHFR and NOS3, were not significantly associated with PE. For the interaction model, SNPs within IGF1 (p = 0.0035) and IL4R (p = 0.0036) gave the most significant results. This study is one of the most comprehensive genetic association studies of PE to date, including an evaluation of offspring genotypes that have rarely been considered in previous studies. Although we did not identify statistically significant evidence of association for any of the candidate loci evaluated here after adjusting for multiple testing using the false discovery rate, additional compelling evidence exists, including multiple SNPs with nominally significant p values in COL1A1 and the IL1A region, and previous reports of association for IL1A, to support continued interest in these genes as candidates for PE. Identification of the genetic regulators of PE may have broader implications, since women with PE are at increased risk of death from cardiovascular diseases later in life.
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Papers by Guy M Lenk