diff --git a/forum/__init__.py b/forum/__init__.py
index 3fa31c34..43406aba 100644
--- a/forum/__init__.py
+++ b/forum/__init__.py
@@ -2,4 +2,4 @@
 Openedx forum app.
 """
 
-__version__ = "0.5.1"
+__version__ = "0.5.2"
diff --git a/forum/api/users.py b/forum/api/users.py
index 9ebd808c..fbe5608b 100644
--- a/forum/api/users.py
+++ b/forum/api/users.py
@@ -9,6 +9,7 @@
 
 from django.http import HttpRequest
 from forum.backend import get_backend
+from forum.backends.mysql.api import MySQLBackend
 from forum.constants import FORUM_DEFAULT_PAGE, FORUM_DEFAULT_PER_PAGE
 from forum.serializers.thread import ThreadSerializer
 from forum.serializers.users import UserSerializer
@@ -137,14 +138,19 @@ def retire_user(
     user = backend.get_user(user_id)
     if not user:
         raise ForumV2RequestError(f"user not found with id: {user_id}")
-    backend.update_user(
-        user_id,
-        data={
-            "email": "",
-            "username": retired_username,
-            "read_states": [],
-        },
-    )
+
+    # Prepare update data
+    data = {
+        "username": retired_username,
+        "read_states": [],
+    }
+
+    # MongoDB backend owns user data and should blank email during retirement
+    # MySQL backend shares auth_user with LMS - LMS manages email field
+    if not isinstance(backend, MySQLBackend):
+        data["email"] = ""
+
+    backend.update_user(user_id, data=data)
     backend.unsubscribe_all(user_id)
     backend.retire_all_content(user_id, retired_username)
 
diff --git a/forum/backends/mysql/api.py b/forum/backends/mysql/api.py
index 9feb0f79..b8d3b070 100644
--- a/forum/backends/mysql/api.py
+++ b/forum/backends/mysql/api.py
@@ -1359,7 +1359,7 @@ def replace_username(user_id: str, username: str) -> None:
         try:
             user = User.objects.get(id=user_id)
             user.username = username
-            user.save()
+            user.save(update_fields=["username"])
         except User.DoesNotExist as exc:
             raise ValueError("User does not exist") from exc
 
@@ -2439,8 +2439,10 @@ def update_user(user_id: str, data: dict[str, Any]) -> int:
         except ObjectDoesNotExist:
             return 0
 
+        user_fields_to_update = []
         if "username" in data:
             user.username = data["username"]
+            user_fields_to_update.append("username")
         # MySQL backend does not update auth_user.email (LMS manages it)
         if "default_sort_key" in data:
             forum_user.default_sort_key = data["default_sort_key"]
@@ -2451,7 +2453,8 @@ def update_user(user_id: str, data: dict[str, Any]) -> int:
             # Then delete ReadState records
             user_read_states.delete()
 
-        user.save()
+        if user_fields_to_update:
+            user.save(update_fields=user_fields_to_update)
         forum_user.save()
         return 1
 
@@ -2461,7 +2464,7 @@ def replace_username_in_all_content(user_id: str, username: str) -> None:
         try:
             user = User.objects.get(pk=user_id)
             user.username = username
-            user.save()
+            user.save(update_fields=["username"])
 
             # Update author_username in all content
             Comment.objects.filter(author=user).update(author_username=username)