Hedgehog Ligands and Receptors Are Deregulated in Myelodysplastic Syndromes

The Hedgehog pathway has an important role in self-renew of normal and leukemic stem cells and is upregulated in myeloid leukemias, however there are no studies regarding the Hedgehog pathway in myelodysplastic syndromes (MDS). Hedgehog ligands (Sonic hedgehog [SHh], Indian hedgehog [IHh], and Desert hedgehog [DHh]) are produced by stromal cells and bind to the receptor Patched (PTCH). This binding causes activation of Smoothened (SMO) receptor, resulting in downstream transcription of target genes.

To evaluate Hedgehod pathway components in MDS.

Bone marrow (BM) samples were collected from 39 MDS (25 low risk, 14 high risk-WHO 2008) patients and 26 healthy donors (HD). Relative expressions of PTCH and SMO were obtained by Real Time PCR. For immunohistochemistry, BM biopsies were collected from 21 MDS (17 low risk and 4 high risk) patients and 7 megaloblastic anemia (MA) were used as control. The BM sections were stained with antibodies for DHh, SHh and c-Kit and the percentage of stained nucleated cells was based on an average of 4 high-powered fields.

Hedeghog receptors PTCH and SMO were overexpressed in MDS BM cells compared to normal BM as follows; PTCH: [median (min-max)] healthy donors= 2.23 (0.42–9.22); low risk= 6.09 (0.41–25.28); high risk= 3.97 (0.42– 21.01); HD vs low risk and HD vs high risk p= 0.02; SMO: healthy donors= 2.33 (0.00–16.11); low risk= 14.79 (1.89– 41.93); high risk= 34.44 (8.04– 164.28)]; HD vs low risk and HD vs high risk p<0.001. Immunohistochemistry assays showed a higher expression of Hedgehog ligands in MDS bone marrow compared to control. For DHh, the number of stained cells in low risk MDS were higher than in MA [MA = 102(84 –183), low risk= 196(69 – 317) high risk 159(131 – 236)]; MA vs low risk p=0.018 and MA vs high risk p= 0.11. Furthermore, SHh staining was 2 and 2.5 fold higher in low and high risk MDS, respectively, compared to MA [MA= 47(18 – 74), low risk 98.25(53 – 129), high risk 116.25 (93 – 125)] MA vs low risk p= 0.001, MA vs high risk p=0.01. Similar to SHh, c-Kit staining was higher in MDS cases as follows: MA= 95.3(61 – 114), low risk= 106(57–136), high risk= 95.3(61 – 114). Interestingly, a high correlation was found between c-kit and DHh (p=0.002, r=0.63) or c-kit and SHh (p=0.001, r=0.7).

To our knowledge, this is the first study of the Hedgehog pathway in MDS. We observed overexpression of Hedgehog receptors and ligands. Furthermore, there is a correlation between these ligands and a marker for hematopoietic stem/progenitors cells. According to these data, we propose that deregulation of Hedgehog in MDS may occur in abnormal progenitors found in MDS bone marrow.

No relevant conflicts of interest to declare.