EXHIBIT A

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended, the undersigned agree to the joint filing on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the Common Stock of Proteon Therapeutics, Inc. and further agree that this agreement be included as an exhibit to such filing. Each party to the agreement expressly authorizes each other party to file on its behalf any and all amendments to such statement. Each party to this agreement agrees that this joint filing agreement may be signed in counterparts.

In evidence whereof, the undersigned have caused this Agreement to be executed on their behalf this 4^th day of February, 2015.

MPM BIO IV NVS STRATEGIC FUND, L.P.
By:	MPM BioVentures IV GP LLC,
	its General Partner
By:	MPM BioVentures IV LLC,
	its Managing Member
By:	/s/ Luke Evnin
	Name: Luke Evnin
	Title: Member
MPM BIOVENTURES IV GP LLC		MPM BIOVENTURES IV LLC
By:	MPM BioVentures IV LLC,	By:	/s/ Luke Evnin
	its Managing Member	Name:	Luke Evnin
		Title:	Member
By:	/s/ Luke Evnin
Name:	Luke Evnin
Title:	Member
By:	/s/ Luke Evnin	By:	/s/ Ansbert Gadicke
	Name: Luke Evnin		Name: Ansbert Gadicke
By:	/s/ Vaughn M. Kailian	By:	/s/ James Paul Scopa
	Name: Vaughn M. Kailian		Name: James Paul Scopa
By:	/s/ Todd Foley
	Name: Todd Foley

Page 14 of 14