title: Potential regulatory role of calsequestrin in platelet Ca(2+)  homeostasis and its association with platelet hyperactivity in  diabetes mellitus.
abstract: BACKGROUND
  Altered Ca(2+) homeostasis contributes significantly to platelet hyperactivity in diabetes mellitus. Calsequestrin (CSQ), as a Ca(2+) buffer protein in the sarcoplasmic reticulum, also regulates the Ca(2+) release process in muscles. We hypothesized that CSQ may be expressed in platelets, but is altered and involved in diabetic platelet Ca(2+) abnormalities and hyperaggregability.
  
  
  METHODS
  CSQ expression in platelets from streptozotocin-induced type 1 diabetes rats, type 2 diabetes volunteers and Goto-Kakizaki rats were analyzed by western blotting and RT-qPCR. Platelet Ca(2+) and aggregation were evaluated with Fura2 and an aggregometer, respectively.
  
  
  RESULTS
  Platelets from diabetic patients and rats exhibited increased resting Ca(2+) levels, and hyperactive Ca(2+) and aggregation responses to agonists. This enhanced basal Ca(2+) was largely dependent on intracellular Ca(2+) and insensitive to inositol 1,4,5-trisphosphate receptor (IP(3)R) antagonism. Additionally, the expression of the skeletal CSQ isotype (CSQ-1) was detected in both rat and human platelets, but its levels were significantly lowered in diabetic platelets as compared with normal platelets. Impairment of CSQ by trifluoperazine caused concentration-dependent Ca(2+) release in normal platelets and HEK293 cells. Knocking down CSQ-1 in HEK293 cells resulted in increased leakage of Ca(2+), which was also insensitive to IP(3)R inhibition, and exaggerated Ca(2+) release following carbachol treatment.
  
  
  CONCLUSIONS
  Downregulation of CSQ-1 in diabetic platelets and impairment of CSQ-1 in normal cells leads to disturbed Ca(2+) release, demonstrating a potential role for CSQ-1 in the regulation of the platelet Ca(2+) release process and a possible causal contribution to diabetic platelet hyperactivity.
authors: Department of Pharmacology, Capital Medical University, Beijing, China.
authors: Z
authors: Z
authors: Zhu
authors: H
authors: H
authors: Zhou
authors: X
authors: X
authors: Yu
authors: L
authors: L
authors: Chen
authors: H
authors: H
authors: Zhang
authors: S
authors: S
authors: Ren
authors: Y
authors: Y
authors: Wu
authors: Dali
authors: D
authors: Luo
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002155:Calsequestrin / Q000502:physiology*; D003920:Diabetes Mellitus / Q000097:blood*; D015536:Down-Regulation; D006706:Homeostasis; D006801:Humans; D015539:Platelet Activation; D051381:Rats
chemical_list: D002155:Calsequestrin; D002118:Calcium