The Effect of Growth Hormone Administration on the Regulation of Mitochondrial Apoptosis in-Vivo

Abstract

The purpose of this study was to determine whether recombinant human growth hormone (rhGH) would show any significant effects on the expression of apoptosis regulating proteins in peripheral blood mononuclear cells (PBMCs). Additionally, the potential for post-transcriptional regulation of gene expression by miRNA was assessed in two cellular compartments, the cytosol and the mitochondria. Ten male subjects were subcutaneously injected with either rhGH (1 mg) or saline (0.9%) for seven consecutive days in a double-blinded fashion. Blood sampling was undertaken prior to treatment administration and over a period of three weeks following treatment cessation. Bcl-2 and Bak gene and protein expression levels were measured in PBMCs, while attention was also directed to the expression of miR-181a and miR-125b, known translational inhibitors of Bcl-2 and Bak respectively. Results showed that rhGH significantly decreased Bak protein concentrations compared to placebo samples for up to 8 days post treatment. While cytosolic miRNA expression was not found to be significantly affected by rhGH, measurement of the expression of miR-125b in mitochondrial fractions showed a significant down-regulation eight days post-rhGH administration. These findings suggest that rhGH induces short-term anti-apoptotic effects which may be partially mediated through a novel pathway that alters the concentration of mitochondrially-associated miRNAs.

Keywords: Bcl-2 proteins; growth hormone; mito-miRNAs; mitochondrial apoptosis.

Figure 1

(A) Protein concentrations of Bak from peripheral blood mononuclear cell (PBMC) mitochondrial extracts in recombinant human growth hormone (rhGH) treated compared to placebo treated samples; (B) Protein concentrations of Bcl-2 from PBMC mitochondrial extracts in rhGH treated compared to placebo treated samples. (* p < 0.05 compared to placebo).

Figure 1

(A) Protein concentrations of Bak from peripheral blood mononuclear cell (PBMC) mitochondrial extracts in recombinant human growth hormone (rhGH) treated compared to placebo treated samples; (B) Protein concentrations of Bcl-2 from PBMC mitochondrial extracts in rhGH treated compared to placebo treated samples. (* p < 0.05 compared to placebo).

Figure 2

(A) Changes from baseline measurements in the expression of Bak mRNA levels from PBMCs in rhGH treated compared to placebo treated samples; (B) Changes from baseline measurements in the expression of Bcl-2 mRNA levels from PBMCs in rhGH treated compared to placebo treated samples.

Figure 2

(A) Changes from baseline measurements in the expression of Bak mRNA levels from PBMCs in rhGH treated compared to placebo treated samples; (B) Changes from baseline measurements in the expression of Bcl-2 mRNA levels from PBMCs in rhGH treated compared to placebo treated samples.

Figure 3

(A) Changes from baseline measurements in the expression of miR-125b miRNA levels from the cytosol of PBMCs in rhGH treated compared to placebo treated samples; (B) Changes from baseline measurements in the expression of miR-181a miRNA levels from the cytosol of PBMCs in rhGH treated compared to placebo treated samples; (C) Changes from baseline measurements in the expression of miR-125b miRNA levels from isolated PBMC mitochondria in rhGH treated compared to placebo treated samples; (D) Changes from baseline measurements in the expression of miR-181a miRNA levels from isolated PBMC mitochondria in rhGH treated compared to placebo treated samples. (* p < 0.05 compared to placebo).

Figure 3

(A) Changes from baseline measurements in the expression of miR-125b miRNA levels from the cytosol of PBMCs in rhGH treated compared to placebo treated samples; (B) Changes from baseline measurements in the expression of miR-181a miRNA levels from the cytosol of PBMCs in rhGH treated compared to placebo treated samples; (C) Changes from baseline measurements in the expression of miR-125b miRNA levels from isolated PBMC mitochondria in rhGH treated compared to placebo treated samples; (D) Changes from baseline measurements in the expression of miR-181a miRNA levels from isolated PBMC mitochondria in rhGH treated compared to placebo treated samples. (* p < 0.05 compared to placebo).