Background/Purpose:

The TβRIIΔk-fib transgenic (TG) mouse model of scleroderma carries a fibroblast-specific TGFβ receptor II mutation resulting in balanced up-regulation of TGFβ signalling and replicates key fibrotic and vasculopathic features of scleroderma, including susceptibility to lung fibrosis and pulmonary hypertension. This study examines evidence of PPAR pathway perturbation in whole tissue or explanted cells from adult or neonatal TG mice compared with wildtype (WT) littermates. Lanifibranor (formerly known as IVA337) is a new chemical entity that activates all PPAR isoforms and is undergoing clinical trials in scleroderma at present.

Methods:

Gene expression differences between whole skin biopsies, fibroblasts or aortic smooth muscle cells (aSMCs) from TβRIIΔk-fib and WT littermate mice (n=3 each group) were quantified using MouseRef-8v1.1 expression BeadChips (Illumina, USA). In total, 42 microarray gene expression profiles were analysed. After normalisation (global; Bioconductor Lumi), the genes were ranked according to differential expression. Data were expressed as pairwise analysis comparing the mean expression of two groups (t test), with FDR correction for multiple testing (number of tests/rank of p value). The PPAR pathway gene list obtained from ttp://software.broadinstitute.org/gsea/msigdb/cards/KEGG_PPAR_SIGNALING_PATHWAY was cross-referenced with each microarray. Within the GSEA cohort of genes the number with significant differential expression or a trend to difference (P< 0.10) in analysis was determined. A total list of 12800 genes were tested.

Results:

The genes within the PPAR pathway showing either significant difference (p<0.05) or trend of difference are summarised in Table 1 below. Overall, 11 genes showed significant difference between WT and TG explant cells and 82% (n=9) were reduced in the TG cells. 25 genes showed a trend of difference in ≥1 of the test substrates and the majority, 18 (72%), were down-regulated in TG mice. This suggested down-regulation of the PPAR pathway in the TbRIIDk-fib mouse model. As shown in Table 1, there were most differences for the aSMCs and this is notable as the altered phenotype of these in culture is likely to reflect an altered in vivo environment, with elevated TGFβ activity in the vessel wall rather than intrinsic SMC abnormalities; the SMC do not express the transgene.

Conclusion:

As expected, whole tissue is less informative that explanted cells with whole skin showing no significantly differentially expressed genes. These results are not indicative of highly dysregulated PPAR pathway expression, although overall there is a signal that the PPAR pathway, assessed by GSEA, may be reduced in TG mice. This trend is seen most often in aSMC explant culture. This mouse model provides a potential platform for in vivo experiments to provide mechanistic support for trials of lanifibranor in scleroderma.

Table 1.

Italicised trend only (p<0.10), others p<0.05

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/evidence-for-altered-peroxisome-proliferator-activated-receptor-ppar-pathway-activity-in-a-transgenic-mouse-model-of-scleroderma-t%ce%b2rii%ce%b4k-fib-analysis-of-mouse-skin-lung-and-explanted-c/