To the Editor:
In an interesting recent contribution to this journal, Laser et al. (1) have presented interesting data on the senescence in uterine fibroids of usual type. A subset of 33/86 fibroids was analyzed for possible correlations between the proliferative index as determined by the percentage of Ki-67 immunopositive cells and the percentage of β‑galactosidase positive cells.
This study revealed that tumor senescence was inversely correlated with the Ki-67 index as well as with the size of the fibroids. In order to quantify the expression of β‑galactosidase on the transcript level we have used quantitative RT-PCR (qRT-PCR) to determine its mRNA in a series of 27 uterine fibroids along with that of Ki-67. Interestingly, we found a statistically significant (p < 0.05) positive correlation between the expression of β-galactosidase and the tumor size (n = 22) and neither positive nor negative correlation between β‑galactosidase mRNA and Ki‑67 mRNA.
Both results do not necessarily exclude each other because the results on a single cell basis may differ from an average level for the whole cell population as reflected by the results of qRT-PCR. Recently, we had been able to show that the p19Arf-network seems to be a key driver of senescence in fibroids (2) assuring their genomic stability via p53. Hence, senescence can be interpreted to result from overpacing of that system either affecting single cells or even the whole tumor. Thus, the same mechanism that efficiently protects fibroids against malignant transformation may be responsible for growth restrictions frequently observed in these tumors (3).
Dominique Nadine Markowski, Dipl.- Biol.a
Burkhard Maria Helmke, M.D.b
Jörn Bullerdiek, Ph.D.a,c
aCenter of Human Genetics
University of Bremen
bInstitute of Pathology
University of Heidelberg
cSmall Animal Clinic
University of Veterinary Medicine and Research Cluster of Excellence “REBIRTH”
1. Laser J, Lee P, Wei J-J. Cellular senescence in usual type uterine leiomyoma. Fertil Steril 2010;93:2020–6.
2. Markowski DN, von Ahsen I, Nezhad MH, Wosniok W, Helmke BM, Bullerdiek J. HMGA2 and the p19Arf-TP53-CDKN1A axis: a delicate balance in the growth of uterine leiomyomas. Genes Chromosomes Cancer. 2010 Aug;49(8):661-8.
3. Peddada SD, Laughlin SK, Miner K, Guyon JP, Haneke K, Vahdat HL, et al. Growth of uterine leiomyomata among premenopausal black and white women. Proc Natl Acad Sci USA 2008;105:19887–92.
Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2010.08.013
The Authors Respond:
We are grateful for the comments from Markowski et al. regarding our recent publication on cellular senescence in uterine leiomyoma (1).
Based on their recent study conducted in 22 leiomyomas by qRT-PCR (2), Markowski et al pointed out that 1) large leiomyomas had significantly high β-galactosidase expression; 2) there was no difference between β-galactosidase and Ki-67 expression. These two findings were different from those in our recent study published in this journal (1). The differences between these two studies are interesting and related to the question of how senescence happens in leiomyomas.
Markowski et al. proposed that senescence in leiomyomas can be the results in balance of leiomyoma growth and oncogene stress through regulating HMGA2-P53-CDKN1A axis (2). We like this idea of oncogene induced senescence in leiomyomas and this was supported in HMGA2 positive tumors, but was unclear in HMGA2 negative tumor population (the later accounting for about 70% of leiomyoma population). In addition, the role of aging-related senescence in leiomyoma maybe equally important (3). For examples, loss of telomere was found to be common in leiomyomas (4), the rate of senescence was higher in older women and there is no difference in the level of senescence between HMGA2 positive and HMGA2 negative tumors (1).
In terms of tumor size and senescence, we have two comments. First, although we found a trend of high level of senescence in smaller tumors and low senescence in larger ones, the findings were statistically insignificant (p>0.05) due to large standard errors (1). Second, sampling in different regions of large tumors may be impact the results due to possibly regional effects on gene expression (5). We collected tumor sections of all large tumors from the region next to the peripheral zone, where higher rates of cell proliferation and ER and PR expression than central zone were noted (5). We assume that the selection of tissue samples may affect the results.
Ki-67 is a cell proliferative marker that is highly expressed in proliferative cells (G1 to M). Immunohistochemistry stain for Ki-67 is a very sensitive method which can detect a low level of Ki-67 positive cells, such as usual type leiomyomas with Ki-67 index of 1-5%. We are not certain whether Ki-67 expression detected by RT-PCR and immunohistochemical stain can be compared if tumors have low levels of Ki-67, particular at individual cell level.
We acknowledge the contribution of the study by Markowski et al. in this subject and the role of cellular senescence in relation to leiomyoma growth deserves further investigations.
Jian-Jun Wei, M.D.a
Jordan Laser, M.D.b
Peng Lee, M.D., Ph.D.b
aDepartment of Pathology
Northwestern University School of Medicine
bDepartment of Pathology
New York University School of Medicine
New York, New York
1. Laser J, Lee P, Wei JJ. Cellular senescence in usual type uterine leiomyoma. Fertil Steril 2010; 93:2020-6.
2. Markowski DN, von Ahsen I, Nezhad MH, Wosniok W, Helmke BM, Bullerdiek J. HMGA2 and the p19Arf-TP53-CDKN1A axis: a delicate balance in the growth of uterine leiomyomas. Genes Chromosomes Cancer 2010; 49:661-8.
3. Collado M, Blasco MA, Serrano M. Cellular senescence in cancer and aging. Cell 2007; 130:223-33.
4. Bonatz G, Frahm SO, Andreas S, Heidorn K, Jonat W, Parwaresch R. Telomere shortening in uterine leiomyomas. Am J Obstet Gynecol 1998; 179:591-6.
5. Wei JJ, Zhang XM, Chiriboga L, Yee H, Perle MA, Mittal K. Spatial differences in biologic activity of large uterine leiomyomata. Fertil Steril 2006; 85:179-87.
Published online in Fertility and Sterility doi:10.1016/j.fertnstert.2010.08.012