O36 – The Genomic Expression of Aged Murine Hematopoietic Stem Cells after Polytrauma Indicates a Failure to Support Development of Innate Immunity
Author(s):
Background: Increased age is associated with worse outcomes after severe trauma. Our work using a mouse polytrauma (PT) model recapitulates this human phenotype – only aged mice have increased susceptibility to Pseudomonal pneumonia after PT. In addition, bronchoalveolar lavages from these aged mice show myeloid cell dysfunction.
Hypothesis: We hypothesize that dysfunctional emergency myelopoiesis by aged murine hematopoietic stem cells (HSCs) explains this phenomenon and is revealed at the genomic level.
Methods: Young (6-12 wks) or old (18-24 mos) B6 mice underwent PT (90 mins shock+long bone fracture+cecectomy). Bone marrow (BM) samples were collected at 1 day. HSCs (Lin-sca-1+ckit+) were isolated through fluorescent cell sorting. Nucleic acids were collected and amplified. Genome-wide expression patterns were analyzed with a log2 transformed expression matrix using RMA. Then genes with significant expression differences were identified using BRB array tools (p<.001,t-test). Using Ingenuity Pathway Analysis® (IPA), significant gene sets from PT mice were compared directly and with healthy controls (p<.001,f-test).
Results: 593 probe sets representing 426 genes discriminated old vs young PT HSCs with 100% correct classification (leave one out cross validation). Functional analysis of these genes showed that only young PT had upregulation of genes involved in leukocyte recruitment and endotoxin shock response pathways (Z-score>2), while only old mice downregulated the quantity of reactive oxygen species pathway (Z-score<2). Only young PT were suggested by IPA as responsive to granulocyte colony stimulating factor as an upstream regulator. Individual gene analysis showed that young PT had significantly increased expression of innate immunity genes, such as chemokine receptor 2, caspase 12, toll-like receptor 1, and chemokine ligand 1; while interleukin (IL) 7, IL10 receptor a, and interferon receptor a/b 1 was reduced in the young. Finally, MHCII antigen presentation genes had significantly decreased fold expression in old PT.
Conclusions: Transcriptomic analysis of murine HSCs after PT indicates the development of innate immunity myeloid cells in the elderly BM is significantly reduced. As HSCs are still plastic, therapies to alter the expression patterns of these cells in the elderly have the potential to improve emergency myelopoiesis in the aged after injury.