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

Abstract

We recently identified Smads1, 5 and 8 as muscle biomarkers in human ALS. In the ALS mouse, these markers are elevated and track disease progression. Smads are signal transducers and become activated upon receptor engagement of ligands from the TGF-β superfamily. Here, we sought to characterize ligands linked to activation of Smads in ALS muscle and their role as biomarkers of disease progression. RNA sequencing data of ALS muscle samples were mined for TGF-β superfamily ligands. Candidate targets were validated by qRT-PCR in a large cohort of human ALS muscle biopsy samples and in the G93A SOD1 mouse. Protein expression was evaluated by Western blot, ELISA and immunohistochemistry. C2C12 muscle cells were used to assess Smad activation and induction. TGF-β1, 2 and 3 mRNAs were increased in ALS muscle samples compared to controls and correlated with muscle strength and Smads1, 2, 5 and 8. In the G93A SOD1 mouse, the temporal pattern of TGF-β expression paralleled the Smads and increased with disease progression. TGF-β1 immunoreactivity was detected in mononuclear cells surrounding muscle fibers in ALS samples. In muscle cells, TGF-β ligands were capable of activating Smads. In conclusion, TGF-β1, 2 and 3 are novel biomarkers of ALS in skeletal muscle. Their correlation with weakness in human ALS and their progressive increase with advancing disease in the ALS mouse suggest that they, as with the Smads, can track disease progression. These ligands are capable of upregulating and activating Smads and thus may contribute to the Smad signaling pathway in ALS muscle.

Muscle Fibers Secrete FGFBP1 to Slow Degeneration of Neuromuscular Synapses during Aging and Progression of ALS

“…1C). As expected, the satellite cell marker Pax7 (Seale et al, 2001) was nearly absent from the TA muscle ribosomal mRNA fractions compared with total muscle mRNA (Fig. 1C).…”

“…Heterozygous animals were intercrossed to produce the homozygous mutant FGFBP1 Ϫ/Ϫ animals. The following mice were obtained from The Jackson Laboratory: SOD1 G93A (RRID:IMSR_JAX:004435; Gurney et al, 1994), Parvalbumin-Cre (RRID:IMSR_JAX:017320; Hippenmeyer et al, 2005; referred to herein as PVCre), Thy1-YFP16 (RRID:IMSR_JAX:003709; Feng et al, 2000; referred to herein as THYFP16), and RiboTag (RRID: IMSR_JAX:011029;Sanz et al, 2009) mice. To visualize motor axons, THYFP16 mice were crossed with SOD1 G93A , FGFBP1 Ϫ/Ϫ , and SOD1 G93A ;FGFBP1 Ϫ/Ϫ mice.…”

ALS skeletal muscle shows enhanced TGF-β signaling, fibrosis and induction of fibro/adipogenic progenitor markers

“…We and others [37] have found augmented levels of TGF-β (three isoforms) in symptomatic hSOD1G93A mice. The pro-fibrotic effect of TGF-β1 have been well-studied, however, controversial evidence regarding TGF-β3 exist.…”

Repeated intramuscular transplantations of hUCB-MSCs improves motor function and survival in the SOD1 G93A mice through activation of AMPK

“…This pathway plays a very important role as a downstream mediator of muscle wasting 33,34 . Additionally, TGF-β1 mRNA and protein expression are significantly increased in skeletal muscles of humans and mice with ALS, and because of this characteristic, TGF-β1 could be used as a muscle biomarker for ALS disease 10 . Previous studies have shown that AMPK activation can prevent muscle wasting induced by inflammation through inhibition of the iNOS/NO pathway 32 .…”

“…Especially, TGF-β1 level was elevated in the serum and plasma of ALS patients 8 . Also, other studies showed that the TGF-β family were significantly increased in human and mice ALS muscle tissue and suggested that TGF-β family could be strong marker of disease progression and onset 9,10 . Especially, oxidative stress induced by TGF-β1 in the skeletal muscle is essential feature of ALS muscle pathology 11 .…”