Most traditional MCBs are designed only for AC applications. AC voltages are quite easy to break because the voltage is alternating from top to zero many times per second. However with DC applications the voltage is always at the top. Therefore it will jump as the breaker tries to open. This means DC breakers must be especially designed to open faster, further and extinguish the voltage arc quickly.
To achieve the 1000V DC rating each pole is looped internally through two break points. This means this breaker looks like a 4 pole, however it is actually only 2 poles (+Vdc and 0Vdc).