Systems genetics uncover new loci containing functional gene candidates in Mycobacterium tuberculosis-infected Diversity Outbred mice.

Mycobacterium tuberculosis, the bacillus that causes tuberculosis (TB), infects 2 billion people across the globe, and results in 8-9 million new TB cases and 1-1.5 million deaths each year. Most patients have no known genetic basis that predisposes them to disease. We investigated the complex genetic basis of pulmonary TB by modelling human genetic diversity with the Diversity Outbred mouse population. When infected with M. tuberculosis, one-third develop early onset, rapidly progressive, necrotizing granulomas and succumb within 60 days. The remaining develop non-necrotizing granulomas and survive longer than 60 days. Genetic mapping using clinical indicators of disease, granuloma histopathological features, and immune response traits identified five new loci on mouse chromosomes 1, 2, 4, 16 and three previously identified loci on chromosomes 3 and 17. Quantitative trait loci (QTLs) on chromosomes 1, 16, and 17, associated with multiple correlated traits and had similar patterns of allele effects, suggesting these QTLs contain important genetic regulators of responses to M. tuberculosis. To narrow the list of candidate genes in QTLs, we used a machine learning strategy that integrated gene expression signatures from lungs of M. tuberculosis-infected Diversity Outbred mice with gene interaction networks, generating functional scores. The scores were then used to rank candidates for each mapped trait in each locus, resulting in 11 candidates: Ncf2, Fam20b, S100a8, S100a9, Itgb5, Fstl1, Zbtb20, Ddr1, Ier3, Vegfa, and Zfp318. Importantly, all 11 candidates have roles in infection, inflammation, cell migration, extracellular matrix remodeling, or intracellular signaling. Further, all candidates contain single nucleotide polymorphisms (SNPs), and some but not all SNPs were predicted to have deleterious consequences on protein functions. Multiple methods were used for validation including (i) a statistical method that showed Diversity Outbred mice carrying PWH/PhJ alleles on chromosome 17 QTL have shorter survival; (ii) quantification of S100A8 protein levels, confirming predicted allele effects; and (iii) infection of C57BL/6 mice deficient for the S100a8 gene. Overall, this work demonstrates that systems genetics using Diversity Outbred mice can identify new (and known) QTLs and new functionally relevant gene candidates that may be major regulators of granuloma necrosis and acute inflammation in pulmonary TB.

The impact of chemokine receptor CX3CR1 deficiency during respiratory infections with Mycobacterium tuberculosis or Francisella tularensis.

Recruitment of immune cells to infection sites is a critical component of the host response to pathogens. This process is facilitated partly through interactions of chemokines with cognate receptors. Here, we examine the importance of fractalkine (CX3CL1) receptor, CX3CR1, which regulates function and trafficking of macrophages and dendritic cells, in the host's ability to control respiratory infections with Mycobacterium tuberculosis or Francisella tularensis. Following low-dose aerosol challenge with M. tuberculosis, CX3CR1(-/-) mice were no more susceptible to infection than wild-type C57BL/6 mice as measured by organ burden and survival time. Similarly, following inhalation of F. tularensis, CX3CR1(-/-) mice displayed similar organ burdens to wild-type mice. CX3CR1(-/-) mice had increased recruitment of monocytes and neutrophils in the lung; however, this did not result in increased abundance of infected monocytes or neutrophils. We conclude that CX3CR1-deficiency affects immune-cell recruitment; however, loss of CX3CR1 alone does not render the host more susceptible to M. tuberculosis or F. tularensis.

Behavioral effects of prenatal exposure to lidocaine in the rat: effects of dosage and of gestational age at administration.

Pregnant Long-Evans hooded rats were dosed via injections into the gum with 3, 6, or 9 mg/kg lidocaine, or vehicle, or were uninjected, on gestational day 4 (GD4), GD11, or GD18. Offspring (8-11 litters/group) were tested on a variety of tests of behavioral development and adult behavior. No effects of any dose at any time of administration were found upon maternal weight gain in gestation, litter size, or initial birth weight or weight gain of the pups. Administration at GD4 produced few effects; only footshock sensitivity showed a significant effect of dosing, although there were trends toward dosing effects on spontaneous alternation. For administration on GD11, lidocaine was associated with slight but significant alterations in sex ratios, and a trend toward drug effects on development of spontaneous alternation. Vehicle administration at this age reduced barbiturate sleep time in offspring and slightly altered footshock sensitivity. Lidocaine dosing on GD18 was associated with a number of significant alterations of behavior, including visual discrimination, shuttlebox avoidance, tail flick, and water maze errors; there were also both vehicle and lidocaine effects on water maze latencies. These data reinforce our previous report that lidocaine may be a behavioral teratogen, and suggest that administration in later gestation in the rat may alter a broader range of behaviors than earlier in gestation.

Alterations in offspring behavior induced by chronic prenatal cocaine dosing.

Sperm-positive female Long-Evans hooded rats were dosed subcutaneously with 10 mg/kg/day cocaine or an equal volume of vehicle (0.9% sterile saline) from gestation day 4 (GD4) through GD18. Offspring were assessed for development of negative geotaxis, righting reflex, spontaneous alternation, and open field activity, and for adult behaviors including DRL-20 acquisition, water maze, visual discrimination, barbiturate sleep time, shuttlebox avoidance, footshock sensitivity, and tail flick latency. Cocaine dosing produced no significant effects on dam weight gain, any measure of litter size and weight, or early postnatal behavioral tests, but there were significant drug effects on development of spontaneous alternation, development of open field activity, DRL-20 acquisition, water maze performance, tail flick, and footshock sensitivity. These data suggest that chronic administration of a modest dose of cocaine during gestation in the rat alters a number of behaviors in the offspring.

Behavioral effects of mid-pregnancy administration of lidocaine and mepivacaine in the rat.

Sperm-positive female Long-Evans hooded rats were injected with 6 mg/kg lidocaine (with epinephrine), 6 mg/kg mepivacaine, or saline, into the masseter muscle of the jaw on Day 11 of gestation. Birth, growth, and litter composition were unaffected by the drug treatment, as was shuttle box acquisition. Offspring of drug-treated dams had longer latencies than controls on the first day of negative geotaxis training, and were more sensitive to electric footshock. Lidocaine-dosed offspring responded less in the presence of the correct cue in the visual discrimination task, and mepivacaine-dosed animals were hypoactive in the open field. In a second study, offspring of lidocaine-dosed dams were slower to develop the righting reflex, made more errors in acquiring a water maze, had longer suppression times in a conditioned suppression task, and had longer latencies in the tail flick test. Dosing had no effect upon birth and growth, shuttle box, or footshock sensitivity. These data demonstrate that midgestational exposure to lidocaine or mepivacaine at a dose near the limits of permissible human exposure produces significant behavioral changes in the offspring. This preliminary study suggests that development of some portion of the central nervous system is altered by such exposure. Further work is required to determine the parameters and the extent of the effect.

Six-month feeding study of fenvalerate in dogs.

Groups of six male and six female Beagle dogs were fed diets containing 0, 250, 500, or 1000 ppm fenvalerate for a period of 6 months. Prominent in-life observations related to treatment were emesis, head shaking, biting of the extremities, ataxia, and tremors. One high-dose male dog was sacrificed in extremis during the study period. Mean body weights of 1000-ppm female dogs were significantly lower than those of controls. Red blood cell counts and hematocrit and hemoglobin values in high-dose male and female dogs were significantly lower than those of controls at most sampling intervals. Serum cholesterol and alkaline phosphatase levels were also increased primarily in the high-dose group. Ophthalmic examination revealed changes in retinal vessel tortuosity in some mid- and high-dose dogs. Hepatic multifocal microgranulomata were observed in control and treated dogs microscopically. These changes increased in incidence and severity with dose and were considered to be related to treatment. Histiocytic cell infiltrate in mesenteric lymph nodes in some 500- and 1000-ppm female and 1000-ppm male dogs was the only other treatment-related microscopic effect.