Abstract
Background
Glutamate carboxypeptidase II (GCPII) is highly upregulated in human IBD and is a therapeutic target under active investigation by our laboratory. We recently published that a spontaneously occurring loss-of-function mutation in dedicator of cytokinesis 2 (Dock2Hsd) that was present in commercially-purchased “wild-type” C57Bl6/NHsd mice increased their sensitivity to DSS-colitis and caused them to closely resemble human IBD with respect to GCPII. The DSS-exposed Dock2Hsd mice had significantly elevated colon GCPII activities and were sensitive to treatment with the GCPII inhibitor, 2-PMPA. We hypothesized that if colitis of the same severity were to be induced in Dock2WT mice, that they would also exhibit heightened colon GCPII activity and would be equally sensitive to 2-PMPA treatment.
Methods
DSS-colitis was induced in weight-, age- and gender-matched C57Bl/6NHsd mice (Dock2Hsd and Dock2WT). Increasing concentrations of DSS were utilized (2.5%-4.0%) and disease activity index was monitored daily. Mice received once daily treatment with vehicle or GCPII inhibitor 2-PMPA (IP).
Results
With increased DSS concentrations (4%), a severe colitis could be established in the Dock2WT mice which closely resembled the disease seen in Dock2Hsd mice induced with 2.5% DSS. Interestingly, despite similarity in DAI scores and disease progression, the GCPII activity in colons of Dock2WT mice (4% DSS) remained significantly lower than that of Dock2Hsd mice (2.5% DSS) (p<0.001, t-test). Further, while 2-PMPA was effective in both groups, higher systemic doses were required in the IBD-resistant Dock2WT mice.
Conclusions
Following identification that the spontaneously occurring mutation Dock2Hsd influences murine DSS-colitis sensitivity and alters the activity of our therapeutic target protein, GCPII, in the colon, we sought to re-establish our DSS model using Dock2WT mice. While we were successfully able to recapitulate disease severity in the Dock2WT mice by increasing the DSS concentration from 2.5% to 4%, the underlying disease biology was not conserved. Despite having comparable DAI scores at study termination, Dock2WT mice had decreased GCPII activity in their colons relative to Dock2Hsd mice and were less sensitive to inhibition with the GCPII inhibitor, 2-PMPA. These data caution that target protein expression must be verified even with subtle changes to experimental method when utilizing the DSS-colitis model.
Metabolite differences between glutamate carboxypeptidase II gene knockout mice and their wild-type littermates after traumatic brain injury: a 7-tesla 1H-MRS study