Identification of novel intracellular functions of the Thrombospondin protein family and characterization of the involvement in the endoplasmic reticulum (ER) protein shuttling, secretion and ER stress activation using in vivo and in vitro models.
Biochemistry
Cardiology, Angiology
Final Report Abstract
Thrombospondin (TSP) proteins are multidomain, matricellular proteins comprised of 5 genes that each share similar domains and have been largely ascribed the same functional characteristics. The TSP protein family is divided in 2 subgroups based on multimerization as trimers, (subgroup A: TSP1 and 2), or as pentamers (subgroup B: TSP3, 4 and 5). TSP4 has been shown to have important intracellular functions by activating AFT6 and mediating an adaptive ER stress response in the heart, thereby having protective effects on heart diseases. These effects are mediated by the C-terminal domains of TSP4, which are also conserved in all other family members. The overall aim of this study was to functionally compare the two TSP subgroups and to elucidate their involvement in cardiac homeostasis and disease. We therefore analyzed TSP1 as a representative of group A and TSP3 as an example of group B. TSP1 and 3 induced a similar ER stress response in vivo. However, overexpression of TSP1 resulted in cardiac atrophy, decreased heart size and cardiac function. This phenotype led to a reduced survival with a median survival rate oft 10 weeks. A hall mark of this phenotype is the reduction of the number capillaries per cardiomyocytes which in turn can lead to a reduced nutrient and oxygen supply to the heart and thereby explain the observed deleterious phenotype. On the contrary, overexpression of TSP3 had no effect on baseline homeostasis and function of the heart. However, in contrast to TSP4, TSP3 hearts showed increased chamber dilation after TAC or MI and lower heart function suggesting that TSP3 also has maladaptive effects. Mechanistically, we found that overexpression of TSP3 reduces the abundance of integrins at the plasma membrane, thereby destabilizing the membrane which might explain the maladaptive effects of TSP3. In contrast to TSP4 knockout animals, which die within the first week of TAC, TSP3 null mice are protected from TAC induced hypertrophy. Moreover, the combination of TSP3/4 double knockout more closely phenocopies the effect of TSP3 deletion, as these mice show a significant reduction in hypertrophy and lung congestion after long term TAC. This is the first study comparing the function of different Thbs isoforms in the heart, which suggests a novel role of TSP3 in negatively regulating Integrin protein abundance and function.
Publications
- Dissection of thrombospondin-4 domains involved in intracellular adaptive ER Stress responsive signaling. Mol Cell Biol. 2015 Oct 12
Brody MJ, Schips TG, Vanhoutte D, Kanisicak O, Karch J, Maliken BD, Blair NS, Sargent MA, Prasad V, Molkentin JD
(See online at https://doi.org/10.1128/MCB.00607-15) - Tumor necrosis factor-α confers cardioprotection through ectopic expression of keratins K8 and K18. Nat Med. 2015 Sep; 21(9):1076-84
Papathanasiou S, Rickelt S, Soriano ME, Schips TG, Maier HJ, Davos CH, Varela A, Kaklamanis L, Mann DL, Capetanaki Y
(See online at https://doi.org/10.1038/nm.3925) - Cathepsin S contributes to the pathogenesis of muscular dystrophy in mice. J. Biol. Chem. jbc.M116.719054
Tjondrokoesoemo A, Schips TG, Sargent MA, Vanhoutte D, Kanisicak O, Prasad V, Lin SJ, Maillet M , Molkentin JD
(See online at https://doi.org/10.1074/jbc.M116.719054) - Genetic overexpression of Serpina3n attenuates muscular dystrophy in mice. Hum Mol Genet. 2016 Mar 15;25(6):1192-202
Tjondrokoesoemo A, Schips T, Kanisicak O, Sargent MA, Molkentin JD
(See online at https://doi.org/10.1093/hmg/ddw005)
