In general I know that the "Je" could have 2 meanings:
1. Quotation. Eg: Areten enemepsha engos khen oushepehmot je peniwt... (Make us worthy to say with thanksgiving "Our fahter..."
Another example: Thai et ere tiestratia enta niangelos teewou nak enkhetc efgw emmos je ouwou emefnouti... (by which the host of angels glorify you saying :Glory to God..." from St. Basil's liturgy
2. For (or because). Eg: je pebnai shop sha eneh (For his mercy endures forever)
Another example: Ounof emmo Maria tivoki ouoh timav je fietkhen peameer... (Rejoice O Mary handmaiden and mother for who is in your arms...
In the context of the Tisagion however, the je seems superfluous. Neither of the 2 meanings above apply here.
I still don't know why it was added, or who added it. But I noticed that the older recordings had it, but most of the new ones don't have je.