<Grid Background="Transparent" RenderTransformOrigin=".5 .5">
                            <Grid.RenderTransform>
                                <RotateTransform Angle="{Binding Path=Angle, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged" />
                            </Grid.RenderTransform>

public class CircleModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        public void RaisePropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = this.PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }
       
        double _angel;
        public double Angel
        {
            get
            {
                return _angel;
            }
            set
            {
                if (_angel == value) return;
                _angel = value;
                RaisePropertyChanged("Angel");
            }
        }