Long-Term Treatment with Rosiglitazone Delays Hematopoietic Recovery in Response to Stress

Rosiglitazone is a peroxisome proliferator activated receptor-γ(PPAR-γ) agonist available to improve glucose metabolism in patients with Type 2 diabetes. Recent evidence suggests that therapeutic use of rosiglitazone have caused unwanted hematological side effects, such as anemia, leukopenia, thrombocytopenia, even pancytopenia. However, others reported that pretreatment with rosiglitazone for 5 days could protect against 5-Fu-induced myelotoxity which is FLT3 dependent. Thus, it is still unclear the exact effects of rosiglitazone treatment on homeostatic and stress hematopoiesis. Rosiglitazone is a potent stimulator of adipogenesis, as it can induce adipogenic differentiation both in vitro and in vivo. Recently, it was reported that adipocyte-rich bone marrow(BM) harbored a decreased frequency of progenitor cells. Furthermore, our laboratory and those of other investigators have demonstrated that BADGE, an inhibitor of PPAR-γ signaling pathway, can improved the hematopoietic recovery in response to stress. So we hypothesize that long-term treatment of rosiglitazone may inhibit the hematopoiesis by inducing BM adipogenesis.

In this study, we first treated C57BL/6J mice with 37.5mg/kg rosiglitazone for six weeks to examine the long-term effect of rosiglitazone on hematopoiesis in vivo. We found that rosiglitazone treatment does not alter body weight or BM function of normal healthy mice. In response to 5-Fu induced hematopoietic stress, rosiglitazone group mice exhibited delayed recovery of WBC and BMMNC. Furthermore, the frequency and absolute number of GMP and CLP cells in rosiglitazone group was decreased at d14 after 5-Fu. Concomitantly, we found that CFU-GM counts of rosiglitazone group BM were significantly decreased when compared with control group mice, while CFU-GEMM counts revealed no difference. However, we didn't observed any alteration in absolute number of LSK cells between the two groups, although rosiglitazone group mice had increased percentage of LSK. These results indicated that rosiglitazone could maintain the HSC compartment while impair myeloid differentiation from myelosuppressive stress, which may explain the delayed hematopoietic recovery in rosiglitazone group.

To answer the question whether the effects of rosiglitazone were directly mediated, in vitro cultures were used. We cultured d3 5-Fu BM cells (BM cells harvested 3 day after 5-FU administration) in the presence of rosiglitazone to detect whether rosiglitazone inhibited hematopoietic progenitor cells in stress condition. Cell proliferation of Lin- cell was unaffected at pharmacologically achievable concentrations of rosiglitazone. However, rosiglitazone at high concentrations (>10μM) significantly inhibit cell proliferation of Lin- cell, which was in agreement with previous reports. To confirm our results, we choose two other TZD drugs to test whether cell proliferation was affected. Similarly, neither troglitazone nor pioglitazone exhibited an inhibition effect on cell proliferation at pharmacologically achievable concentrations. Furthermore, rosiglitazone treatment didn't decrease the numbers of CFU-GM. These data show that rosiglitazone can not directly inhibit cell proliferation or myeloid differentiation of HPC in stress condition.

As long-term treatment of rosiglitazone caused a significant increase of BM adipocytes in mice, we speculated that impaired myeloid differentiation in rosiglitazone group mice may be due to enhanced adipogenesis. We found that rosiglitazone promoted the adipogenic differentiation of two stromal cell lines (C3H10T1/2,M2-10B4). In addition, rosiglitazone treated stromal cell lines significantly inhibited cell proliferation and myeloid differentiation of co-cultured Lin- cells.

In conclusion, rosiglitazone induced BM adipogenesis can impair the myeloid differentiation of hematopoietic stem cell, which may contribute to a significant delay in hematopoietic recovery after chemotherapeutic stress. Further investigation of the molecular mechanism is warranted and may enable the development of therapies effective for suppressed hematopoiesis induced by TZDs.