Subject of article — Simeon's heart (5)
I believe the answer is:
theme
'subject' is the definition.
(theme can mean a topic or subject)
'article simeon's heart' is the wordplay.
'article' becomes 'the' (the definite article in English).
'heart' indicates the central letters.
The centre of 'simeon' is 'me'.
'the'+'me'='THEME'
'of' acts as a link.
(Other definitions for theme that I've seen before include "Subject matter, topic" , "Musical motif" , "Burden" , "notedly subject to variation" , "Topic for discussion" .)