Murine macrophages express abundant insulin-like growth factor-I class I Ea and Eb transcripts.

Abstract

Hemopoietic cells have been reported to synthesize insulin-like growth factor-I (IGF-I) messenger RNA (mRNA), but the relative contribution of specific cell lineages that express these transcripts remains unknown. Reverse transcription and amplification of complementary DNA (cDNA) by the polymerase chain reaction were used to characterize full-length IGF-I mRNA transcripts in murine hemopoietic cells. The identity of transcripts encoding the entire prepropeptide was confirmed by restriction endonuclease digestion, Southern blotting, cloning, and Sanger sequencing. Abundance of IGF-I mRNA transcripts was assessed both by Northern blotting and sensitive ribonuclease protection assays followed by quantification with Phosphor-Imager analysis. Whereas IGF-I cDNA transcripts could be detected in a variety of leukocytes after polymerase chain reaction amplification, IGF-I mRNA was negligible or nondetectable in T and B cell lines and in those tissues containing a predominance of these cell types (e.g. spleen and thymus) by Northern blotting and ribonuclease protection assays. In contrast, elicited peritoneal macrophages, a macrophage cell line, microglia, and bone marrow macrophages differentiated in vitro expressed abundant IGF-I mRNA transcripts, whereas neither a premyeloid cell line nor freshly isolated bone marrow cells expressed significant transcripts. The 5'-identity of macrophage IGF-I transcripts was established using an exon 2-derived IGF-I cDNA probe. All protected transcripts were foreshortened, indicating transcript initiation exclusively within exon 1, characteristic of extra-hepatic IGF-I mRNA. However, at the 3'-end, both IGF-I Ea (lacking exon 5) and IGF-I Eb (containing exon 5) mRNA transcripts were evident, with the Eb product being detected at levels similar to those present in hepatic cellular RNA. A large molecular size (26 kilodaltons) prepro-IGF-I peptide was also detected in macrophage cell lysates by Western blotting. Collectively, our observations show that: 1) among hemopoietic cells, myeloid rather than lymphoid cells are the major source of IGF-I; 2) macrophage IGF-I mRNA consists of class I Ea and Eb transcripts; 3) these transcripts are translated into protein; and 4) expression of IGF-I is directly associated with differentiation of bone marrow macrophages.

Functional Insulin-Like Growth Factor-1/Insulin-Like Growth Factor-1 Receptor-Mediated Circuit in Human and Murine Thymic Epithelial Cells

“…Yamada et al [18]showed that GH stimulated IGF-1 expression by a TEC line obtained from a lymphocyte-rich rat thymoma. The local production of IGF-1 as well as GH has been demonstrated in human and murine thymus [19, 20, 21, 22, 23, 24, 25]. The expression of both GH receptor and IGF-1 receptor has been detected in human and murine thymocytes [25, 26, 27]and in murine TEC [18, 28, 29].…”

Why Should Growth Hormone (GH) Be Considered a Promising Therapeutic Agent for Arteriogenesis? Insights from the GHAS Trial

“…In addition, immune cells have IGF-IR and produce IGF-I. This could be another indirect way to influence these cells by GH [119,120]. All the mentioned cells participate during the vascular wall inflammation needed for collateral enlargement.…”

“…In fact, when CSF-1 lacks many skeletal defects or deformities have been described in animals along with a delayed growth, while the administration of recombinant human CSF-1 corrects these changes [127], suggesting that this factor interacts with the GH/IGF-I axis. Macrophages also produce IGF-I in response to CSF-1 and other stimuli [120,128], and represent one of the main producers of extrahepatic IGF-I [129]. Although at a lower level, other types of the M-CSF family, such as G-CSF or GM-CSF, have the same effect on the production of macrophage IGF-I.…”

The somatotropic axis of the dairy cow revisited

“…Their abundance most likely reflects the complexities of cellular regulation, including the level of translation, intracellular trafficking, and stability of the mRNA to degradation (Lund 1994). The relative abundance of exon 1 and exon 2 transcripts appears to vary according to nutritional and physiological state, circulating GH concentration, developmental regulation, tissue and species (Arkins et al. 1993; Pell et al.…”