Tetrapeptides and compositions comprising tetrapeptides

According to the present invention there is provided a combination of peptides capable of inducing upregulation of a dermal extracellular matrix protein, comprising: a) a first peptide selected from the group consisting of tetrapeptides having the amino acid sequence U-LSXX-Z wherein, according to an internationally recognized single alphabetic code of amino acids, L is used to represent the amino acid leucine and S is used to represent serine, x represents an amino acid independently selected from the group consisting of valine (V), aspartic acid (D), proline (P), and glycine (G); at the N terminal, U is selected from the group consisting of H,-CO-R1,-SO2-R1 or a biotin-based group, and at the C terminal, Z is selected from the group consisting of OH, OR1, NHR1 or NR1R2; r1 and R2 are independently selected from the group consisting of alkyl, aryl, aralkyl, alkylaryl, alkoxy, sugar and aryloxy groups, which may be linear, branched, cyclic, polycyclic, unsaturated, hydroxylated, carbonylated, phosphorylated a