Biology subjects

Black, M. B.

Publications and source records attributed to Black, M. B..

3 recordsLinked to original sources

bioRxiv2024

Investigating the mode of action for wasting produced by tetrachlorodibenzo-p-dioxin (TCDD) in rats using transcriptomics: Evidence for roles of AHR and ARNT in circadian cycling

Single, high doses of TCDD in rats caused wasting, a progressive loss of 30 to 50% body weight and death within several weeks. To identify pathway perturbations at or near doses causing wasting, we examined differentially gene expression (DGE) and pathway enrichment in centrilobular (CL) and periportal (PP) regions of female rat livers following 6 dose levels of TCDD - 0, 3, 22, 100, 300, and 1000 ng/kg/day, 5 days/week for 4 weeks. At the higher doses, rats lost weight, had increased liver/body weight ratios and nearly complete cessation of liver cell proliferation, signs consistent with wasting. DGE curves were left shifted for the CL versus the PP regions. Canonical Phase I and Phase II genes were maximally increased at lower doses and remained elevated at all doses. At lower doses, < 22 ng/kg/day in the CL and < 100 ng/kg/day, upregulated genes showed transcription factor (TF) enrichment for AHR and ARNT. At the mid- and hi-dose doses, there was a large number of downregulated genes and pathway enrichment for DEGs showed downregulation of many cellular metabolism processes including those for steroids, fatty acid metabolism, pyruvate metabolism and citric acid cycle. There was significant TF enrichment of the hi-dose downregulated genes for RXR, ESR1, LXR, PPARalpha. At the highest dose, there was also pathway enrichment with upregulated genes for extracellular matrix organization, collagen formation, hemostasis and innate immune system. TCDD demonstrates most of its effects through binding the aryl hydrocarbon receptor (AHR) while the downregulation of metabolism genes at higher TCDD doses is known to be independent of AHR binding to DREs. Based on our results with DEG, we provide a hypothesis for wasting in which high doses of TCDD shifts circadian processes away from the resting state leading to greatly reduced synthesis of steroids and complex lipids needed for cell growth and producing gene expression signals consistent with an epithelial-to-mesenchymal transition in hepatocytes.

pharmacology and toxicology↗

bioRxiv2023

Impact of gene selection criteria on transcriptomic ontology-based point of departure estimates

Apical effects are typically associated with changes in gene expression, which allows for the use of short- term in life transcriptomic studies to derive biologically relevant points of departure (POD). These methods offer cost savings over conventional toxicology assessments and can derive data from very short-term studies where apical effects may not yet be present. When there is limited or insufficient data for a conventional POD assessment, a transcriptomic screen could provide valuable data for deriving a cellular bioactivity POD for chemical screening and hazard assessment. We used existing transcriptomic data from published 5-day rat in vivo kidney and liver exposures to examine the effect of differential gene expression metrics for the selection of genes used for ontology pathway-based POD derivation. Williams Trend Test (WTT) indicate no gene expression dose-response in 6 instances and ANOVA in one, while DESeq2 detected differentially expressed genes in all instances. The three statistical metrics produced consistent POD values. One chemical (PFOA in liver) showed ontology enrichment indicative of a cytotoxic response at the highest dose, emphasizing the effect which too high a dose can have on the derivation of POD values if such response is not accounted for. Whether the choice of a gene selection metric combining both a statistical significance criterion as well as a minimum magnitude of change threshold affects the sensitivity of POD values depends on the specifics of the dose- response. Existing alternative and complementary analyses could be utilized with existing analyses pipelines to better inform analytical decisions when using transcriptomics and BMD for point of departure determinations.

pharmacology and toxicology↗

bioRxiv2023

Assessing the basal gene expression of cancer cell lines for in vitro transcriptomic toxicology screening

In vitro toxicology has used immortalized cancer cell lines as model human systems for decades. However, these cell lines pose problems in designing toxicity testing programs as they inherently do not represent normal human biology. There is also a huge number of such cell lines to choose from, derived from human cancer cells from nearly every tissue. We explored the idea of using available basal gene expression data (NCI-60 cell line panel and Human GTEx tissue data) to determine if there was sufficient variability in cell line gene expression to group cell lines by relevance to specific human tissues. The transcriptomic analysis suggests that the variability in gene expression in cancer cell lines and in normal human tissue is minimal. The overall basal gene expression of cancer cells lines even overlapped normal human tissue gene expression. While some human tissues (e.g., lung) have basal expression profiles that do not appear to be like any cancer cell line, including cancers that may be derived from the same tissue, most human tissues show basal expression profiles comparable to several cancer cell lines. These results are important to address the genomic baseline and variability of cancer cell lines used for new approach methods of toxicity testing.

bioinformatics↗