PARP1 and thymus neoplasm: TCDD increased cellular senescence in thymus epithelial cells (Fig. 4d,e and Supplementary Fig. S11) and this TCDD effect, like thymus atrophy and hepatosteatosis, was diminished by cotreatment with NAM or PJ34, supporting a role for NAD+ depletion by PARP activity in increased cellular senescence by TCDD (Fig. 4e).