Reuse subquery as in another result
Or is there a way to access a subquery result? 


Sure there are ways, but only in the same query at the next higher level.
You can extend the scope with a CTE, but still limited to the same query (anywhere).
To preserve a derived table across queries in the same session, materialize the result in a temporary table.
Or a regular table (maybe UNLOGGED?) to extend the scope to all sessions.

What's reasonable depends on the details of your installation.

Ideally, you do it all in a single query, in a single query level, even. The difficulty is the return type. You have to combine columns, possibly creating some redundancy in the result. You can either reduce query time or reduce redundant data in the result, but not both. Combining everything into a single JSON column might be an alternative.

To get everything in a single query:

SELECT n.id, n.title, n.description, id_channel 
FROM   community.user_follows uf 
JOIN   community.news         n USING (id_channel)
WHERE  uf.id_user ='3d4c788e0e34657457febba2040297c7';