The Response to Burn Injury in Mice With Human Hematolymphoid Systems

ObjectiveTo develop an animal model of injury that more closely represents the human inflammatory cell response to injury.BackgroundBecause the mouse inflammatory response to burn injury cannot account for the contribution of human-specific genes, animal models are needed to more closely recapitulate the human inflammatory response and improve the translational impact of injury research. To this end, we hypothesized that the human inflammatory cell response to injury could be selectively assessed after severe burn injury using humanized mice.MethodsNOD-Scid-IL2Rγ null mice were transplanted with human hematopoietic CD34+ progenitor cells; their engraftment confirmed and then subjected to 30% total body surface area steam burn injury. Blood, bone marrow, and lung tissue were collected 4 hours after injury and human inflammatory cell mobilization analyzed using flow cytometry and immunohistochemistry.ResultsBurn injury caused mobilization of human inflammatory cells into the systemic circulation. Next, burn injury was accompanied by evidence of histologic lung injury and concomitant mobilization of human CD45+ immune cells into the lung that were associated with increased trafficking of human CD11b+ myeloid cells.ConclusionsThese experiments are the first to demonstrate the suitability of humanized mice for injury research. They offer the possibility to address very specific research questions that are not amenable to traditional mouse models of injury, for example, the emerging role of certain human-specific genes that are either unrepresented or totally absent, from the mouse genome

A Human-Specific α7-Nicotinic Acetylcholine Receptor Gene in Human Leukocytes: Identification, Regulation and the Consequences of CHRFAM7A Expression

The human genome contains a variant form of the α7-nicotinic acetylcholine receptor (α7nAChR) gene that is uniquely human. This CHRFAM7A gene arose during human speciation and recent data suggests that its expression alters ligand tropism of the normally homopentameric human α7-AChR ligand-gated cell surface ion channel that is found on the surface of many different cell types. To understand its possible significance in regulating inflammation in humans, we investigated its expression in normal human leukocytes and leukocyte cell lines, compared CHRFAM7A expression to that of the CHRNA7 gene, mapped its promoter and characterized the effects of stable CHRFAM7A overexpression. We report here that CHRFAM7A is highly expressed in human leukocytes but that the levels of both CHRFAM7A and CHRNA7 mRNAs were independent and varied widely. To this end, mapping of the CHRFAM7A promoter in its 5′-untranslated region (UTR) identified a unique 1-kb sequence that independently regulates CHRFAM7A gene expression. Because overexpression of CHRFAM7A in THP1 cells altered the cell phenotype and modified the expression of genes associated with focal adhesion (for example, FAK, P13K, Akt, rho, GEF, Elk1, CycD), leukocyte transepithelial migration (Nox, ITG, MMPs, PKC) and cancer (kit, kitL, ras, cFos cyclinD1, Frizzled and GPCR), we conclude that CHRFAM7A is biologically active. Most surprisingly however, stable CHRFAM7A overexpression in THP1 cells upregulated CHRNA7, which, in turn, led to increased binding of the specific α7nAChR ligand, bungarotoxin, on the THP1 cell surface. Taken together, these data confirm the close association between CHRFAM7A and CHRNA7 expression, establish a biological consequence to CHRFAM7A expression in human leukocytes and support the possibility that this human-specific gene might contribute to, and/or gauge, a human-specific response to inflammation