Elastomer isoprene rubber compositions contain an effective amount of a polyfunctional coupling system (A) as an inorganic-elastomer filler coupling agent, and (B) at least one elastomer of natural or synthetic rubber; (C) an inorganic filler as reinforcing filler; (D) other conventional constituents or additives comprising one or more vulcanizing agent(s), the polyfunctional coupling system being of the constituents (A1) and (A2): (A1) is at least one coupling agent selected from among the functionalized organosilicon compounds of formula (I): [(G0)3SiO1/2]m[(G0)2SiO2/2]n[G0SiO3/2]o[SiO4/2]p[(G2)a(G1)a′(Z—CO—N═N—CO-A)SiO(3-a-a′)/2]q and (A2) is at least one coupling agent selected among polysulfurated “symmetric” silanes, or sulfurated “asymmetric” silanes.