Expression of Cellular Senesence Associated B-Galactosidase (SABG) Is up-Regulated in Melodysplastic Syndrome
Authors: Kang Loveleen C. , Rocha Kathy , Rollison Dana E , Moscinski Lynn C. , List Alan F. 
Published: April 2020

Age and mutagen related stem cell depletion may contribute to emergence of neoplastic clones. While telomere shortening or dysfunction may initiate replicative senescence and apoptosis, oncogene-induced senescence arising from induction of inflammatory cytokines may precede telomeric changes in neoplastic cells (Cell2008; 133: 1019). Activation of cellular senescence is associated with up-regulation of b-galactosidase activity at pH6 known as ‘senescence-associated’ b-galactosidase (SABG). To investigate the role of senescence in myelodysplastic syndromes (MDS), we evaluated SABG activity in bone marrow cells of newly diagnosed MDS patients (n=18) and age-matched controls (n=9).

METHODS: MDS cases that received no prior treatment other than growth factors were included. All MDS diagnoses were histologically confirmed by bone marrow examination, classified by WHO and categorized into low risk {RA, RCMD, RCMD-RS and del (5q)} (n=10) and high risk groups { RAEB-1, RAEB-2} (n=8). Controls bone marrows were obtained from staging marrows for lymphoid malignancy after confirmed absence of medullary tumor involvement. Cytospins were prepared from bone marrow aspirates and stained using a SABG staining Kit. SABG expression was characterized by average staining intensity and quantitated by the percentage of positive cells according to cell lineage (i.e., megakaryocyte, myeloid, erythroid and lymphoid cells). Staining differences were compared using Vander Waerden Two-Sample Test. Correlations between myeloid SABG expression and, blast percentage or, absolute neutrophil count (ANC); megakaryocyte positivity and platelet count; average positivity and IPSS score among the two WHO groups was analyzed using Spearman coefficient.

RESULTS: SABG expression as measured by mean percentage of positive cells was significantly higher in low risk MDS cases (mean (SD) = 9% (0.090476)) when compared with controls (mean (SD) =1% (0.030923)) (p 0.02). Percentage of SABG-positive myeloid cells was significantly also higher in low risk MDS cases (mean (SD) = 8% (0.077201)) when compared to controls (mean (SD) =1%) (p 0.02). High risk MDS cases also had increased SABG expression as measured by mean percentage of positive cells (mean (SD) = 14% (0.164099)) and percentage of SABG-positive myeloid cells (mean (SD) = 24 % (0.290369)). Similarly, the percentage of SABG positive megakaryocytes was higher in low risk MDS cases (mean (SD) =20 %( 0.312681)) and high risk MDS cases (mean (SD) = 14% (0.2258)) compared to controls (mean (SD) =0% (0.007559)) (p 0.13 and 0.21 respectively). In high risk MDS we found a positive correlation between the percentage of SABG staining myeloid cells and marrow blast percentage (mean (SD) = 9.3750(4.5019)) (0.07702). Moreover, in low risk MDS there was a negative correlation between percentage myeloid cell positivity and absolute neutrophil count (mean (SD) = 2.2 (1.27)) (−0.40122). There was no significant difference in average percentage of SABG staining among IPSS risk categories. SABG positive cells lacked cytologic features of apoptosis or mitosis.

CONCLUSION: MDS is associated with activation of cellular senescence programs in affected hematopoietic precursors. The linkage between myeloid SABG expression and neutropenia and blast percentage suggests that cellular senescence may contribute to maturation impairment and ineffective myelopoiesis.