Smads as muscle biomarkers in amyotrophic lateral sclerosis

Abstract

ObjectiveTo identify molecular signatures in muscle from patients with amyotrophic lateral sclerosis (ALS) that could provide insight into the disease process and serve as biomarkers.MethodsRNA sequencing was performed on ALS and control muscle samples to identify Smad family members as potential markers of disease. Validation studies were performed in a cohort of 27 ALS patients and 33 controls. The markers were assessed in the G93A superoxide dismutase (SOD)1 mouse at different stages of disease and in a model of sciatic nerve injury.ResultsSmad8, and to a lesser extent Smad1 and 5, mRNAs were significantly elevated in human ALS muscle samples. The markers displayed a remarkably similar pattern in the G93A SOD1 mouse model of ALS with increases detected at preclinical stages. Expression at the RNA and protein levels as well as protein activation (phosphorylation) significantly increased with disease progression in the mouse. The markers were also elevated to a lesser degree in gastrocnemius muscle following sciatic nerve injury, but then reverted to baseline during the muscle reinnervation phase.InterpretationThese data indicate that Smad1, 5, 8 mRNA and protein levels, as well as Smad phosphorylation, are elevated in ALS muscle and could potentially serve as markers of disease progression or regression.

Transforming Growth Factor Beta (TGF-β) Is a Muscle Biomarker of Disease Progression in ALS and Correlates with Smad Expression

“…Non-transgenic littermates were used as controls. For the G93A SOD1 mice, clinical progression was evaluated by weight determination and performance on the rotarod as described previously [ 4 ]. End stage disease was determined when the mouse could not right itself after 30 seconds when placed on its side.…”

“…In the ALS mouse, pathological changes can first be detected in muscle and the neuromuscular junction prior to motor neuron loss, indicating that these structures can reflect early disease activity [ 1 – 3 ]. We recently identified members of the Smad family (Smads1, 5, and 8) as muscle biomarkers of disease progression in ALS [ 4 ]. These Smads are upregulated and activated in the ALS mouse at an early stage, before overt clinical signs are present, suggesting they may also be markers of disease onset.…”

Further development of biomarkers in amyotrophic lateral sclerosis

“…The down regulation of SCD1 (Stearoyl-CoA desaturase 1) in the muscle of ALS patients also confirmed the relevant role of muscle in pathogenesis [87]. Recent studies described the involvement of muscle in the motor neuron degeneresence mechanisms through: the UCP1 (uncoupling protein 1) protein [88], SOD1 [89], neurotrophin 4, BMP (Bone morphogenetic) proteins, Smads [55,[90][91][92], Akt and Factor XIIIB [93]. Elf et al [94] recently performed a shotgun proteomics and quantitative dimethyl labeling to evaluate the human skeletal muscle proteome of ALS and reported a panel of 11 proteins.…”

“…Potentially more sensitive thematic transcriptomic approaches focused on pathophysiological mechanisms can also be used. Several RNA expressed in non-neural tissues, such as Smad RNA in muscle, have been proposed as potential ALS biomarkers [55][56]. Studies on the expression of miRNAs found in biological fluids that are considered to be stable, such as CSF, blood and urine could also provide biomarkers in ALS [57][58] through global method i.e.…”

New developments and future opportunities in biomarkers for amyotrophic lateral sclerosis

“…Muscle transcriptome analyses have found that smad1, 5, 8 mRNA and protein levels, as well as Smad phosphorylation, were elevated in ALS muscle. Therefore, muscle smads could serve as potential candidates for ALS biomarkers [ 47 ].…”