Developmentally regulated expression of hemoglobin subunits in avascular tissues

Abstract

We investigated the spatio-temporal profile of hemoglobin subunit expression in developing avascular tissues. Significant up-regulation of hemoglobin subunits was identified in microarray experiments comparing blastocyst inner cell masses with undifferentiated embryonic stem (ES) cells. Hemoglobin expression changes were confirmed using embryoid bodies (derived from in vitro differentiation of ES cells) to model very early development at pre-vascular stages of embryogenesis; i.e. prior to hematopoiesis. We also demonstrate, using RT-PCR, Western blotting and immunocytochemistry, expression of adult and fetal mouse hemoglobin subunits in the avascular ocular lens at various stages of development and maturation. Hemoglobin proteins were expressed in lens epithelial cells (cytoplasmic) and cortical lens fiber cells (nuclear and cellsurface-associated); however, a sensitive heme assay demonstrated negligible levels of heme in the developing lens postnatally. Hemoglobin expression was also observed in the developing eye in corneal endothelium and retinal ganglion cells. Gut sections showed, in addition to erythrocytes, hemoglobin protein staining in rare, individual villus epithelial cells. These results suggest a paradigm shift: hemoglobin subunits are expressed in the avascular lens and cornea and in prehematopoietic embryos. It is likely, therefore, that hemoglobin subunits have novel developmental roles; the absence of the heme group from the lens would indicate that at least some of these functions may be independent of oxygen metabolism. The pattern of expression of hemoglobin subunits in the perinuclear region during lens fiber cell differentiation, when denucleation is taking place, may indicate involvement in the apoptosis-like signaling processes occurring in differentiating lens fiber cells.

Hypoxia Up-Regulates Expression of Hemoglobin in Alveolar Epithelial Cells

“…Similar results were obtained by another group, demonstrating that the expression of hemoglobin appears to be absent from fully differentiated ATI cells (7). The expression of nonerythroid hemoglobins was also reported in activated macrophages from adult mice, cells of the ocular lens, and putatively in embryonic neurons (8)(9)(10)(11). Here, we further characterize the expression of hemoglobin by ATII cells, and identify the mRNAs of a number of transcription factors and other genes that are traditionally associated with hemoglobin biosynthesis in erythroid precursors.…”

“…These studies all support a role for globin genes in protecting against hypoxic injury. Recently, the discovery of hemoglobin in the lens and cornea of prehematopoietic murine embryos suggests a developmental role for hemoglobin, independent of oxygen metabolism (11). The presence of hemoglobin in pulmonary epithelial cells could play a major role in protection against the stress of functioning in the most highly oxidative cellular environment within the mammalian body.…”

Evolutionary and Functional Properties of a Two-Locus β-Globin Polymorphism in Indian House Mice

“…In contrast to the allelic differences in cysteine content that distinguish products of Hbb d and Hbb s in M. domesticus and M. musculus, amino acid differences between the d minor and p minor isoHbs of M. castaneus have no effect on the metabolism of thiol reactants or intraerythrocytic redox balance (which can affect aspects of the host immune response to pathogenic infection). Nonetheless, we cannot rule out the possibility that the b-globin polymorphism in M. castaneus affects some unknown biochemical function, especially in light of recent discoveries concerning the expression of globin chain monomers in nonerythroid cells (e.g., Liu et al 1999;Mansergh et al 2008;Nishi et al 2008;Biagioli et al 2009;Richter et al 2009;Schelshorn et al 2009). In light of our experimental results, we conclude that amino acid differences between products of the d minor and p minor alleles are functionally inconsequential with regard to the respiratory physiology of house mice.…”

Cell therapy using retinal progenitor cells shows therapeutic effect in a chemically-induced rotenone mouse model of Leber hereditary optic neuropathy

“…Hba-a1 is expressed in the apoptosis-like processes that take place as differentiating lens fibre cells lose their nuclei, without dying. 24 It is also present in the retina, optic nerve head macroglia and RGCs, and is upregulated in glaucomatous eyes and is prominently expressed in retinal glia. 23 Upregulation could relate to antiapoptotic function, or be protective against damage-induced hypoxia.…”

“…23 Upregulation could relate to antiapoptotic function, or be protective against damage-induced hypoxia. 23,24 DISCUSSION Treatment of rotenone-damaged retinas with RPCs generates a notable therapeutic effect. The mode of action of RPC therapy in this LHON model is unknown, however, there are a number of possibilities.…”