Intrathecal Vector Delivery in Juvenile Rats via Lumbar Cistern Injection.

Gene therapy is a powerful technology to deliver new genes to a patient for the treatment of disease, be it to introduce a functional gene, inactivate a toxic gene, or provide a gene whose product can modulate the biology of the disease. The delivery method for the therapeutic vector can take many forms, ranging from intravenous infusion for systemic delivery to direct injection into the target tissue. For neurodegenerative disorders, it is often desirable to skew transduction towards the brain and/or spinal cord. The least invasive approach to target the entire central nervous system involves injection into the cerebrospinal fluid (CSF), allowing the therapeutic to reach a large fraction of the central nervous system. The safest approach to deliver a vector into the CSF is the lumbar intrathecal injection, where a needle is introduced into the lumbar cistern of the spinal cord. This technique, also known as a lumbar puncture, has been widely used in neonatal and adult rodents and in large animal models. While the technique is similar across species and developmental stages, subtle differences in size, structure, and elasticity of tissues surrounding the intrathecal space require accommodations in the approach. This article describes a method for performing lumbar puncture in juvenile rats to deliver an adeno-associated serotype 9 vector. Here, 25-35 µL of vector were injected into the lumbar cistern, and a green fluorescent protein (GFP) reporter was used to evaluate the transduction profile resulting from each injection. The benefits and challenges of this approach are discussed.

A pilot study of neonatal GALT gene replacement using AAV9 dramatically lowers galactose metabolites in blood, liver, and brain and minimizes cataracts in GALT-null rat pups.

Classic galactosemia (CG) is a rare metabolic disorder that results from profound deficiency of galactose-1-P uridylyltransferase (GALT). Despite early detection by newborn screening and rapid and lifelong dietary restriction of galactose, which is the current standard of care, most patients grow to experience a broad constellation of long-term complications. The mechanisms underlying these complications remain unclear and likely differ by tissue. Here we conducted a pilot study testing the safety and efficacy of GALT gene replacement using our recently-described GALT-null rat model for CG. Specifically, we administered AAV9.CMV.HA-hGALT to seven GALT-null rat pups via tail vein injection on day 3 of life; eight GALT-null pups injected with PBS served as the negative control, and four GALT+ heterozygous pups injected with PBS served as the positive control. All pups were returned to their nursing mothers, weighed daily, and euthanized for tissue collection 2 weeks later. Among the AAV9-injected pups in this study, we achieved GALT levels in liver ranging from 64% to 595% wild-type, and in brain ranging from 3% to 42% wild-type. In liver, brain, and blood samples from these animals we also saw a striking drop in galactose, galactitol, and gal-1P. Finally, all treated GALT-null pups showed dramatic improvement in cataracts relative to their mock-treated counterparts. Combined, these results demonstrate that GALT restoration in both liver and brain of GALT-null rats by neonatal tail vein administration using AAV9 is not only attainable but effective.

Low-level maternal exposure to nicotine associates with significant metabolic perturbations in second-trimester amniotic fluid.

Decades of public health research have documented that smoking in pregnancy poses significant health risks to both mother and child. More recent studies have shown that even passive maternal exposure to secondhand smoke associates with negative birth outcomes. However, the mechanisms linking exposure to outcomes have remained obscure. As a first step toward defining the metabolic consequence of low-level nicotine exposure on fetal development, we conducted an untargeted metabolomic analysis of 81 paired samples of maternal serum and amniotic fluid collected from karyotypically normal pregnancies in the second trimester. By comparing the m/z and retention times of our mass spectral features with confirmed standards, we identified cotinine, a nicotine derivative, and used the calculated cotinine concentrations to classify our maternal serum samples into exposure groups using previously defined cut-offs. We found that cotinine levels consistent with low-level maternal exposure to nicotine associated with distinct metabolic perturbations, particularly in amniotic fluid. In fact, the metabolic effects in amniotic fluid of ostensibly low-level exposed mothers showed greater overlap with perturbations previously observed in the sera of adult smokers than did the perturbations observed in the corresponding maternal sera. Dysregulated fetal pathways included aspartate and asparagine metabolism, pyrimidine metabolism, and metabolism of other amino acids. We also observed a strong negative association between level of maternal serum cotinine and acetylated polyamines in the amniotic fluid. Combined, these results confirm that low-level maternal nicotine exposure, indicated by a maternal serum cotinine level of 2-10ng/mL, is associated with striking metabolic consequences in the fetal compartment, and that the affected pathways overlap those perturbed in the sera of adult smokers.

Genetic and functional studies reveal a novel noncoding variant in GALT associated with a false positive newborn screening result for galactosemia.

BACKGROUND: Classic galactosemia (CG) is a potentially lethal genetic disorder that results from profound loss of galactose-1-phosphate uridylyltransferase (GALT). CG is detected by newborn screening (NBS) in many countries; however, conclusive diagnosis can be complex due to broad and overlapping ranges of GALT activity. Molecular studies can also be complex due to allelic heterogeneity at the GALT locus. METHODS: We conducted both biochemical and molecular follow-up studies for an infant flagged by NBS for possible galactosemia. To clarify the diagnosis we also conducted biochemical and RNA studies of lymphoblasts prepared from the child and one parent. RESULTS: We identified a novel noncoding GALT variant, c.377+17C>T, that was homozygous in the child and heterozygous in both parents. The child and both parents also showed diminished GALT activity in red blood cells, and transformed lymphoblasts from the child and one parent further showed diminished GALT activity. However, qRT-PCR studies demonstrated apparently normal GALT mRNA levels in lymphoblasts, and Gal-1P values measured in the child following galactose exposure in infancy and at 1 year were normal. CONCLUSIONS: These results highlight the existence of rare but apparently benign variants in GALT and underscore the need for functional studies to distinguish pathogenic from benign variants.

Manganese-based superoxide dismutase mimics modify both acute and long-term outcome severity in a Drosophila melanogaster model of classic galactosemia.

AIMS: The goal of this study was to use two manganese (Mn)-based superoxide dismutase (SOD) mimics to test the hypothesis that reactive oxygen species contribute to both acute and long-term outcomes in a galactose-1P uridylyltransferase (GALT)-null Drosophila melanogaster model of classic galactosemia. RESULTS: We tested the impact of each of two Mn porphyrin SOD mimics, MnTnBuOE-2-PyP(5+), and MnTE-2-PyP(5+), (i) on survival of GALT-null Drosophila larvae reared in the presence versus absence of dietary galactose and (ii) on the severity of a long-term movement defect in GALT-null adult flies. Both SOD mimics conferred a significant survival benefit to GALT-null larvae exposed to galactose but not to controls or to GALT-null larvae reared in the absence of galactose. One mimic, MnTE-2-PyP(5+), also largely rescued a galactose-independent long-term movement defect otherwise seen in adult GALT-null flies. The survival benefit of both SOD mimics occurred despite continued accumulation of elevated galactose-1P in the treated animals, and studies of thiolated proteins demonstrated that in both the presence and absence of dietary galactose MnTE-2-PyP(5+) largely prevented the elevated protein oxidative damage otherwise seen in GALT-null animals relative to controls. INNOVATION AND CONCLUSIONS: Our results confirm oxidative stress as a mediator of acute galactose sensitivity in GALT-null Drosophila larvae and demonstrate for the first time that oxidative stress may also contribute to galactose-independent adult outcomes in GALT deficiency. Finally, our results demonstrate for the first time that both MnTnBuOE-2-PyP(5+) and MnTE-2-PyP(5+) are bioavailable and effective when administered through an oral route in a D. melanogaster model of classic galactosemia.

Oxidative stress contributes to outcome severity in a Drosophila melanogaster model of classic galactosemia.

Classic galactosemia is a genetic disorder that results from profound loss of galactose-1P-uridylyltransferase (GALT). Affected infants experience a rapid escalation of potentially lethal acute symptoms following exposure to milk. Dietary restriction of galactose prevents or resolves the acute sequelae; however, many patients experience profound long-term complications. Despite decades of research, the mechanisms that underlie pathophysiology in classic galactosemia remain unclear. Recently, we developed a Drosophila melanogaster model of classic galactosemia and demonstrated that, like patients, GALT-null Drosophila succumb in development if exposed to galactose but live if maintained on a galactose-restricted diet. Prior models of experimental galactosemia have implicated a possible association between galactose exposure and oxidative stress. Here we describe application of our fly genetic model of galactosemia to the question of whether oxidative stress contributes to the acute galactose sensitivity of GALT-null animals. Our first approach tested the impact of pro- and antioxidant food supplements on the survival of GALT-null and control larvae. We observed a clear pattern: the oxidants paraquat and DMSO each had a negative impact on the survival of mutant but not control animals exposed to galactose, and the antioxidants vitamin C and α-mangostin each had the opposite effect. Biochemical markers also confirmed that galactose and paraquat synergistically increased oxidative stress on all cohorts tested but, interestingly, the mutant animals showed a decreased response relative to controls. Finally, we tested the expression levels of two transcripts responsive to oxidative stress, GSTD6 and GSTE7, in mutant and control larvae exposed to galactose and found that both genes were induced, one by more than 40-fold. Combined, these results implicate oxidative stress and response as contributing factors in the acute galactose sensitivity of GALT-null Drosophila and, by extension, suggest that reactive oxygen species might also contribute to the acute pathophysiology in classic galactosemia.

Functional overlap between conserved and diverged KH domains in Saccharomyces cerevisiae SCP160.

The K homology (KH) domain is a remarkably versatile and highly conserved RNA-binding motif. Classical KH domains include a characteristic pattern of hydrophobic residues, a Gly-X-X-Gly (GXXG) segment, and a variable loop. KH domains typically occur in clusters, with some retaining their GXXG sequence (conserved), while others do not (diverged). As a first step towards addressing whether GXXG is essential for KH-domain function, we explored the roles of conserved and diverged KH domains in Scp160p, a multiple-KH-domain-containing protein in Saccharomyces cerevisiae. We specifically wanted to know (1) whether diverged KH domains were essential for Scp160p function, and (2) whether diverged KH domains could functionally replace conserved KH domains. To address these questions, we deleted and/or interchanged conserved and diverged KH domains of Scp160p and expressed the mutated alleles in yeast. Our results demonstrated that the answer to each question was yes. Both conserved and diverged KH domains are essential for Scp160p function, and diverged KH domains can function in place of conserved KH domains. These findings challenge the prevailing notions about the requisite features of a KH domain and raise the possibility that there may be more functional KH domains in the proteome than previously appreciated.

Determinants of function and substrate specificity in human UDP-galactose 4'-epimerase.

UDP-galactose 4'-epimerase (GALE) interconverts UDP-galactose and UDP-glucose in the final step of the Leloir pathway. Unlike the Escherichia coli enzyme, human GALE (hGALE) also efficiently interconverts a larger pair of substrates: UDP-N-acetylgalactosamine and UDP-N-acetylglucosamine. The basis of this differential substrate specificity has remained obscure. Recently, however, x-ray crystallographic data have both predicted essential active site residues and suggested that differential active site cleft volume may be a key factor in determining GALE substrate selectivity. We report here a direct test of this hypothesis. In brief, we have created four substituted alleles: S132A, Y157F, S132A/Y157F, and C307Y-hGALE. While the first three substitutions were predicted to disrupt catalytic activity, the fourth was predicted to reduce active site cleft volume, thereby limiting entry or rotation of the larger but not the smaller substrate. All four alleles were expressed in a null-background strain of Saccharomyces cerevisiae and characterized in terms of activity with regard to both UDP-galactose and UDP-N-acetylgalactosamine. The S132A/Y157F and C307Y-hGALE proteins were also overexpressed in Pichia pastoris and purified for analysis. In all forms tested, the Y157F, S132A, and Y157F/S132A-hGALE proteins each demonstrated a complete loss of activity with respect to both substrates. In contrast, the C307Y-hGALE demonstrated normal activity with respect to UDP-galactose but complete loss of activity with respect to UDP-N-acetylgalactosamine. Together, these results serve to validate the wild-type hGALE crystal structure and fully support the hypothesis that residue 307 acts as a gatekeeper mediating substrate access to the hGALE active site.

Structural analysis of the Y299C mutant of Escherichia coli UDP-galactose 4-epimerase. Teaching an old dog new tricks.

UDP-galactose 4-epimerase catalyzes the interconversion of UDP-Gal and UDP-Glc during normal galactose metabolism. The mammalian form of the enzyme, unlike its Escherichia coli counterpart, can also interconvert UDP-GalNAc and UDP-GlcNAc. One key feature of the epimerase reaction mechanism is the rotation of a 4-ketopyranose intermediate in the active site. By comparing the high resolution x-ray structures of both the bacterial and human forms of the enzyme, it was previously postulated that the additional activity in the human epimerase was due to replacement of the structural equivalent of Tyr-299 in the E. coli enzyme with a cysteine residue, thereby leading to a larger active site volume. To test this hypothesis, the Y299C mutant form of the E. coli enzyme was prepared and its three-dimensional structure solved as described here. Additionally, the Y299C mutant protein was assayed for activity against both UDP-Gal and UDP-GalNAc. These studies have revealed that, indeed, this simple mutation did confer UDP-GalNAc/UDP-GlcNAc converting activity to the bacterial enzyme with minimal changes in its three-dimensional structure. Specifically, although the Y299C mutation in the bacterial enzyme resulted in a loss of epimerase activity with regard to UDP-Gal by almost 5-fold, it resulted in a gain of activity against UDP-GalNAc by more than 230-fold.