Solar neutrinos emitted by fusion reactions occurring in the Sun provide a unique and direct way to study the interior of our stars: a precise knowledge of reactions producing neutrinos is mandatory to use these neutrinos as probes. Unfortunately many key reactions are still missing high precision data. The goal of nuclear astrophysics is to provide a deeper knowledge of the nuclear reactions ruling the stellar evolution and the synthesis of the elements of the periodic table. Deep underground in the Gran Sasso laboratory, the cross-sections of the several hydrogen burning reactions have been measured right down to the energies of astrophysical interest by the LUNA (Laboratory for Underground Nuclear Astrophysics) Collaboration. At the end of 2018, a new window to the study of helium and carbon burning will by opened by the installation in Hall B of Gran Sasso of a new 3.5 MV single-ended accelerator (LUNA-MV) able to provide hydrogen, helium and carbon high current beams: this new facility will allow to aggress the study of key reactions shaping the evolution of massive stars towards their final fate. The present contribution is aimed to summarize the main results obtained during the solar phase of LUNA and to highlight their influence on our understanding of the properties of the neutrino and of the Sun. Finally, the future of LUNA during the next decade will be outlined.