Mice with sclerostin gene deletion are resistant to the severe sublesional bone loss induced by spinal cord injury.

Bone loss after spinal cord injury (SCI) is rapid, severe, and refractory to interventions studied to date. Mice with sclerostin gene deletion are resistant to the severe sublesional bone loss induced by SCI, further indicating pharmacological inhibition of sclerostin may represent a promising novel approach to this challenging medical problem. INTRODUCTION: The bone loss secondary to spinal cord injury (SCI) is associated with several unique pathological features, including the permanent immobilization, neurological dysfunction, and systemic hormonal alternations. It remains unclear how these complex pathophysiological changes are linked to molecular alterations that influence bone metabolism in SCI. Sclerostin is a key negative regulator of bone formation and bone mass. We hypothesized that sclerostin could function as a major mediator of bone loss following SCI. METHODS: To test this hypothesis, 10-week-old female sclerostin knockout (SOST KO) and wild type (WT) mice underwent complete spinal cord transection or laminectomy (Sham). RESULTS: At 8 weeks after SCI, substantial loss of bone mineral density was observed at the distal femur and proximal tibia in WT mice but not in SOST KO mice. By µCT, trabecular bone volume of the distal femur was markedly decreased by 64 % in WT mice after SCI. In striking contrast, there was no significant reduction of bone volume in SOST KO/SCI mice compared with SOST KO/sham. Histomorphometric analysis of trabecular bone revealed that the significant reduction in bone formation rate following SCI was observed in WT mice but not in SOST KO mice. Moreover, SCI did not alter osteoblastogenesis of marrow stromal cells in SOST KO mice. CONCLUSION: Our findings demonstrate that SOST KO mice were protected from the major sublesional bone loss that invariably follows SCI. The evidence indicates that sclerostin is an important mediator of the marked sublesional bone loss after SCI, and that pharmacological inhibition of sclerostin may represent a promising novel approach to this challenging clinical problem.

Focal adhesion kinase signaling is decreased 56 days following spinal cord injury in rat gastrocnemius.

STUDY DESIGN: Descriptive study. OBJECTIVES: The goal of this study was to determine the effects of spinal cord injury (SCI) on aspects of the focal adhesion kinase (FAK) signaling pathway 56 days post injury in rat gastrocnemius. SETTING: This study was conducted in Bronx, NY, USA. METHODS: Three-month-old male Wistar rats were exposed to either a sham surgery (n=10) or complete T4 spinal cord transection (n=10). Rats were killed 56 days following surgery and the muscle was collected. Following homogenization, proteins of the FAK pathway were analyzed by western immunoblotting or reverse transcription-qPCR. In addition, cellular markers for proteins that target the degradation of FAK were investigated. RESULTS: SCI resulted in significantly lower levels of total and phosphorylated FAK, cSrc and p70S6k, and a trend for increased FRNK protein expression. SCI did not change levels of the α7 or ß1 integrin subunits, total or phosphorylated ERK1/2, phosphorylated Akt and TSC2 or total p70S6k. SCI resulted in a greater expression of total Akt. mRNA expression of FAK and the α7 or ß1 integrins remained unchanged between sham and SCI groups. Caspase-3/7 activity and Trim72 mRNA and protein expression remained unchanged following SCI. CONCLUSION: SCI results in diminished FAK signaling and is independent of ERK1/2 and Akt. SCI has no effect on mRNA levels for genes encoding components of the focal adhesion 56 days after injury.

Testosterone reduced methylprednisolone-induced muscle atrophy in spinal cord-injured rats.

STUDY DESIGN: Male rats with complete transections of the spinal cord were administered vehicle or methylprednisolone (MP) for 24 h, with or without infusion, for 7 days, of testosterone at either a replacement or low pharmacological doses. Muscles were collected at 7 days after SCI. OBJECTIVE: The objective of this study is to determine, in a rat model of complete spinal cord transection, whether testosterone reduces muscle atrophy or upregulates muscle atrophy-linked genes, induced by 24 h of MP administration at doses comparable to those prescribed in man during the period immediately following acute spinal cord injury (SCI) in an attempt to preserve neurological function. RESULTS: MP significantly reduced the mass of triceps, soleus and plantaris, and significantly increased expression of genes that promote atrophy. Testosterone significantly reduced muscle atrophy induced by MP, but did not prevent it; there was no difference between low- or high-dose testosterone in reducing MP-induced muscle loss. High-dose testosterone reduced expression of muscle atrophy genes more than did low dose. Testosterone-induced declines in mRNA levels for these atrophy-associated genes did not correlate well with protection against MP-induced muscle atrophy. CONCLUSIONS: MP induces marked and lasting changes in the biology of muscle that persisted for at least 7 days, or 6 days after MP has been eliminated from the body. Testosterone partially protected against muscle atrophy and gene expression changes caused by 1 day of MP.

The administration of high-dose methylprednisolone for 24 h reduced muscle size and increased atrophy-related gene expression in spinal cord-injured rats.

OBJECTIVE: Administration after spinal cord injury (SCI) of methylprednisolone (MP) for 24-48 h has been suggested to improve functional outcome. The safety of this approach has been questioned because of the known adverse effects of glucocorticoids on skeletal muscle and the immune system. The purpose of this study was to explicitly test adverse effects of regimen of MP administration on skeletal muscle. STUDY DESIGN: Male rats underwent spinal cord transection at T9-T10, followed by an intravenous injection of MP and subsequent infusion of MP for 24 h. RESULTS: MP significantly reduced the weight of the triceps, soleus, plantaris and gastrocnemius muscles, with the greatest effect being a 63% decrease in triceps weight (for example, muscle above the level of lesion) at 7 days; below the level of lesion, gastrocnemius weight was reduced by 33% by SCI alone, and by 45% by SCI and MP. Centralized nuclei were found in myofibers of the gastrocnemius and triceps from the MP-SCI group, but not other groups. MP increased expression in the triceps, soleus and plantaris of FOXO1, MAFbx, MuRF1 and REDD1 at 1 day, and, in plantaris, at 7 days. CONCLUSIONS: Thus, 1 day of MP at a dose comparable to those routinely employed in clinical practice immediately after SCI resulted in marked atrophy of functionally intact muscle above the level of lesion, and worsened atrophy of paralyzed muscle below the level of lesion, associated with elevations in expression of four genes involved in pathways associated with muscle atrophy.