Update: Blizzard has scaled back the nerfs to Ana in the latest update to the Overwatch PTR. The damage on her Biotic Rifle remains at the reduced value (60, down from 80) but the change to her Biotic Grenade has been reverted. It now once again does 60 damage to enemies and 100 healing to Ana and her allies.
"Ana had the biggest changes in this patch, and upon testing, feedback, and talking about it a ton internally, we decided to pull back on the nerfs a bit for this patch," principal designer Geoff Goodman explained in a forum post. "The damage reduction on her weapon is significant, but if this ends up not being enough we can re-visit some further tuning. We don't want to swing her balance too wildly within a single patch."
A few other heroes received additional tweaks as well. The change to Zenyatta's Orb of Discord has also been reverted, meaning it once again cannot target enemies through barriers. However, the weapon spread on his Orb of Destruction has been removed. It's a small change that many Zen players won't even notice, as the weapon spread was nearly negligible to begin with, but there is a difference—most noticeable when using his alternate fire at full charge. Here's a gif of what the change looks like, via Redditor soulofdragon: