Poster #051, UC Davis Health System
Investigating Mitochondrial Fusion in a Cellular Model of Snyder Robinson Syndrome
Mentors: Bryan Le, PhD and Fernando Fierro, PhD
Snyder Robinson Syndrome (SRS) is a rare genetic disorder characterized by fragile bones. SRS is caused by loss-of-function mutations in the Spermine Synthase (SMS) gene, which encodes the enzyme converting spermidine into spermine. Although these polyamines are important for skeletal health, it remains unclear how SMS deficiency induces impaired mineralization. When our lab modeled SRS in mesenchymal stem cells (MSCs) either chemically, by inhibiting SMS using N-cyclohexyl-1,3-propanediamine (CDAP), or genetically (using a shRNA), there was a significant reduction in mineralization and proliferation, as well as excess mitochondrial fusion. It was recently described that secretion of mitochondria is critical during osteogenesis. Since this process is likely impaired due to excess mitochondrial fusion, we examined if inhibiting mitochondrial fusion could rescue SRS phenotypes. To test this, we cultured MSCs in osteogenic inductive media with MYLS22, which reduces mitochondrial fusion. We measured mineralization through Alizarin Red S (ARS) staining and mitochondrial biomass using nonyl-acridine orange (NAO). We measured proliferation in standard media through direct cell counts using a hemacytometer. CDAP-treated MSCs show reduced mineralization, compared to control. When MSCs were cultured with CDAP and MYLS22, there was no appreciable rescue in mineralization. Similarly, MSCs cultured with CDAP and MYLS22 did not change NAO signal, when compared to CDAP-only MSCs. After 2 days in culture, MSCs treated with CDAP show a decrease in proliferation while MSCs treated with CDAP and MYLS22 proliferated similarly to untreated control. However, this rescue in proliferation disappears by day 4. Altogether, our work suggests that, in SRS, mitochondrial dynamics play an important role in proliferation but not in osteogenesis. Further studies are needed to determine the optimal dose of MYLS22 to balance mitochondrial fusion and fission to promote osteogenesis in SRS.