Rosiglitazone induces the unfolded protein response, but has no significant effect on cell viability, in monocytic and vascular smooth muscle cells.
Given the safety concerns expressed over negative cardiovascular outcomes resulting from the clinical use of rosiglitazone, and the view that rosiglitazone exerts PPARγ-independent effects alongside its insulin-sensitising PPARγ-dependent effects, we hypothesised that rosiglitazone may trigger Unfolded Protein Responses (UPRs) due to disruptions in [Ca(2+)](i) homeostasis within two cardiovascular cell types: monocytic (MM6) and vascular smooth muscle (A7r5) cells. In microsomal samples derived from both cell types, pre-incubation with rosiglitazone rapidly (30min) brought about concentration-dependent PPARγ-independent inhibition of Ca(2+)ATPase activity (IC(50) ∼2μM). Fluo-3 fluorimetric data demonstrated in intact cells that 1h treatment with 1 or 10μM rosiglitazone caused Ca(2+) ions to leak into the cytoplasm. Gene expression analysis showed that within 4h of rosiglitazone exposure, the UPR transcription factor XBP-1 was activated (likely due to corresponding ER Ca(2+) depletion), and the UPR target genes BiP and SERCA2b were subsequently upregulated within 24-72h. After 72h 1 or 10μM rosiglitazone treatment, microsomal Ca(2+)ATPase activity increased to >2-fold of that seen in control microsomes, while [Ca(2+)](i) returned to basal, indicating that UPR-triggered SERCA2b upregulation was responsible for enhanced enzymatic Ca(2+) sequestration within the ER. This appeared to be sufficient to replenish ER Ca(2+) stores and restore normal cell physiology, as cell viability levels were not decreased due to rosiglitazone treatment throughout a 2-week study. Thus, incubation with 1-10μM rosiglitazone triggers the UPR, but does not prove cytotoxic, in cells of the cardiovascular system. This observation provides an important contribution to the current debate over the use of rosiglitazone in the clinical treatment of Type-2 Diabetes.
Caddy
J
J
Centre for Biomedical Sciences, Cardiff School of Health Sciences, University of Wales Institute Cardiff, Cardiff CF5 2YB, UK.
Isa
S
S
Mainwaring
L S
LS
Adam
E
E
Roberts
A
A
Lang
D
D
Morris
R H K
RH
Thomas
A W
AW
Webb
R
R
D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D015870:Gene Expression / Q000187:drug effects; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D009000:Monocytes / Q000187:drug effects* / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D000077154:Rosiglitazone; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism; D045162:Thiazolidinediones / Q000009:adverse effects / Q000494:pharmacology*; D014157:Transcription Factors / Q000378:metabolism; D056811:Unfolded Protein Response; D014665:Vasodilator Agents / Q000494:pharmacology*; D000071717:X-Box Binding Protein 1
D004268:DNA-Binding Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D007004:Hypoglycemic Agents; D000071701:Regulatory Factor X Transcription Factors; D045162:Thiazolidinediones; D014157:Transcription Factors; D014665:Vasodilator Agents; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; D000077154:Rosiglitazone; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C506946:ATP2A2 protein, human; D002118:Calcium