Modeling Snyder-Robinson Syndrome in multipotent stromal cells reveals impaired mitochondrial function as a potential cause for deficient osteogenesis

Abstract

Patients with Snyder-Robinson Syndrome (SRS) exhibit deficient Spermine Synthase (SMS) gene expression, which causes neurodevelopmental defects and osteoporosis, often leading to extremely fragile bones. To determine the underlying mechanism for impaired bone formation, we modelled the disease by silencing SMS in human bone marrow - derived multipotent stromal cells (MSCs) derived from healthy donors. We found that silencing SMS in MSCs led to reduced cell proliferation and deficient bone formation in vitro, as evidenced by reduced mineralization and decreased bone sialoprotein expression. Furthermore, transplantation of MSCs in osteoconductive scaffolds into immune deficient mice shows that silencing SMS also reduces ectopic bone formation in vivo. Tag-Seq Gene Expression Profiling shows that deficient SMS expression causes strong transcriptome changes, especially in genes related to cell proliferation and metabolic functions. Similarly, metabolome analysis by mass spectrometry, shows that silencing SMS strongly impacts glucose metabolism. This was consistent with observations using electron microscopy, where SMS deficient MSCs show high levels of mitochondrial fusion. In line with these findings, SMS deficiency causes a reduction in glucose consumption and increase in lactate secretion. Our data also suggests that SMS deficiency affects iron metabolism in the cells, which we hypothesize is linked to deficient mitochondrial function. Altogether, our studies suggest that SMS deficiency causes strong transcriptomic and metabolic changes in MSCs, which are likely associated with the observed impaired osteogenesis both in vitro and in vivo.

Development of a Redox-Sensitive Spermine Prodrug for the Potential Treatment of Snyder Robinson Syndrome

“…Further experiments revealed that the prodrug unresponsive cells imported the prodrug but failed to effectively convert it to spermine suggesting a lower cellular reduction potential in specific SRS cell types. This is consistent with the known mitochondrial defects noted in SRS cells with specific mutations. , Further experiments showed that one could convert the recalcitrant fibroblast line to a prodrug-responsive line via preincubation with N -acetylcysteine (NAC).…”

“…Previous studies have demonstrated that the SMS deficiency impairs mitochondrial function. , The dysfunction of mitochondria is linked to the oxidative state of the cell because mitochondria can be damaged by reactive oxygen species (ROS). Because the ROS hydrogen peroxide is a byproduct of spermidine catabolism, we speculated that the oxidative stress generated from the metabolism of the imbalanced polyamine pools in SRS cells may affect mitochondrial function and lower cellular reduction potential. , In short, ROS load could explain why certain SRS cells were recalcitrant to the prodrug.…”

“…Previous studies have demonstrated that the SMS deficiency impairs mitochondrial function. , The dysfunction of mitochondria is linked to the oxidative state of the cell because mitochondria can be damaged by reactive oxygen species (ROS). Because the ROS hydrogen peroxide is a byproduct of spermidine catabolism, we speculated that the oxidative stress generated from the metabolism of the imbalanced polyamine pools in SRS cells may affect mitochondrial function and lower cellular reduction potential. , In short, ROS load could explain why certain SRS cells were recalcitrant to the prodrug. Since polyamine import activity was still operative in the recalcitrant cell line, we speculated that the prodrug entered these cells but failed to release spermine due to a lower cellular reduction potential caused by ROS.…”

Novel Hemizygous Missense Variant of Spermine Synthase (<b><i>SMS</i></b>) Gene Causes Snyder-Robinson Syndrome in a Four-Year-Old Boy

“…To better define the osteoporosis of SRS, Albert et al [2015] performed detailed studies on affected individuals and provided the first evidence supporting that SRS patients lose osteoblast and osteoclast activity and that the low bone density ocurring in SRS most likely arises by an intrinsic cellular process [Albert et al, 2015]. Furthermore, Ramsay et al [2019] modeled the disease by silencing SMS in multipotent stromal cells in human bone marrow and found what led to reduced cell proliferation and deficient bone formation in vitro, as evidenced by reduced mineralization and decreased bone sialoprotein expression. This study suggests that SMS deficiency causes strong transcriptomic and metabolic changes in multipotent stromal cells, which are possibly associated with the observed impaired osteogenesis both in vitro and in vivo [Ramsay et al, 2019].…”

“…Furthermore, Ramsay et al [2019] modeled the disease by silencing SMS in multipotent stromal cells in human bone marrow and found what led to reduced cell proliferation and deficient bone formation in vitro, as evidenced by reduced mineralization and decreased bone sialoprotein expression. This study suggests that SMS deficiency causes strong transcriptomic and metabolic changes in multipotent stromal cells, which are possibly associated with the observed impaired osteogenesis both in vitro and in vivo [Ramsay et al, 2019].…”