Automatic transmissions are not mechanically linked to the engine (unlike manual transmissions), they are linked by your transmission fluid only. That gives us 3 things to consider:
Gears: Since they are mechanically linked to your wheels, your actual speed (not engine speed) is what dictates how fast the gears are spinning.
Torque converter: This is mechanically connected to your gears and linked through fluid to the engine. Higher engine speeds will make it spin faster, and that alone is unlikely to cause wear since we are talking about accelerating, we will only spend a small amount of time at high RPMs. Remaining at high RPMs may cause metal fatigue though, but I think something else may break first.
Engine: The RPMs are in the engine, therefore the engine is what is absorbing the vibrations, the torque and the heat. Higher RPMs mean more of all 3. Heat can be managed by the cooling system, but even with everything running optimally, there's a limit on how long you can maintain high RPMs before the temperature starts going up (you have a gauge for this). Many engines will auto-shutdown when the temperature gets too high in order to avoid engine damage. That leaves torque and vibration, and these 2 are likely to stress metal parts of the engine. Although there are rubber bushings and other related contraptions to absorb vibrations, they still contribute to wear, and the higher torque of higher RPMs is putting more strain on several components inside the engine, chiefly the crankshaft, piston rods and just about all the seals. Depending on the relative strength of each design, the weakest will let go first.
All that being said, don't worry about high RPMs too much. Drive the way you drive, and feel free to push high RPMs on occasion, just stay safely away from the redline on your tachometer. My redline is at 6900 RPMs, and I regularly push my engine to about 5000 RPMs when I really want to go, since high RPMs is where all my torque is. There is nothing special about my engine and I'm nearing 300,000 km on it. :)