Decreased circulating ErbB4 ectodomain fragments as a read-out of impaired signaling function in amyotrophic lateral sclerosis

Abstract

ErbB4 is a transmembrane receptor tyrosine kinase that binds to neuregulins to activate signaling. Proteolytic cleavage of ErbB4 results in release of soluble fragments of ErbB4 into the interstitial fluid. Disruption of the neuregulin-ErbB4 pathway has been suggested to be involved in the pathogenesis of amyotrophic lateral sclerosis (ALS). This study assesses whether soluble proteolytic fragments of the ErbB4 ectodomain (ecto-ErbB4) can be detected in cerebrospinal fluid (CSF) and plasma, and if the levels are altered in ALS. Immunoprecipitation combined with mass spectrometry or western blotting analyses confirmed the presence of ecto-ErbB4 in human CSF. Several anti-ErbB4-reactive bands, including a 55 kDa fragment, were detected in CSF. The bands were generated in the presence of neuregulin-1 (Nrg1) and were absent in plasma from ErbB4 knockout mice. Ecto-ErbB4 levels were decreased in CSF from ALS patients (n = 20) and ALS with concomitant frontotemporal dementia patients (n = 10), compared to age-matched controls (n = 13). A similar decrease was found for the short ecto-ErbB4 fragments in plasma of the same subjects. Likewise, the 55-kDa ecto-ErbB4 fragments were decreased in the plasma of the two transgenic mouse models of ALS (SOD1G93A and TDP-43A315T). Intracellular ErbB4 fragments were decreased in the frontal cortex from SOD1G93A mice, indicating a reduction in Nrg-dependent induction of ErbB4 proteolytic processing, and suggesting impaired signaling. Accordingly, overexpression of Nrg1 induced by an adeno-associated viral vector increased the levels of the ecto-ErbB4 fragment in the SOD1G93A mice. We conclude that the determination of circulating ecto-ErbB4 fragments could be a tool to evaluate the impairment of the ErbB4 pathway and may be a useful biomarker in ALS.

Serum biomarkers associated with baseline clinical severity in young steroid-naïve Duchenne muscular dystrophy boys

“…It is tempting to speculate that serum ERBB4 levels could be a biomarker for mitochondrial dysfunction in skeletal muscle in DMD. This is further supported by a recent study showing that decreased levels of circulating of ERBB4 ectodomain is strongly associated with impaired ERBB4 pathway in cerebrospinal fluid and plasma of ALS patients ( 43 ). ERBB4 is also highly expressed in smooth muscle as is dystrophin, while smooth muscle lacks dystrophin in DMD.…”

The Skeletal Muscle Emerges as a New Disease Target in Amyotrophic Lateral Sclerosis

“…Thus, myotube and MN co-cultures derived from FUS -ALS patient iPSCs showed impaired endplate maturation, and FUS mutant mice had decreased endplate surface area [ 230 ]. Besides, the neurotrophic factor neuroregulin 1 ( NRG-1 ) participates in NMJ maintenance and AchR stability, and Nrg-1-ErbB4 receptor signaling alterations may be involved in the pathogenesis of ALS [ 304 ]. In mutant Sod1 mice, adenoviral overexpression of Nrg-1 by intramuscular adenoviral injection prevented denervation, activated collateral reinnervation, and stabilized AChR clusters through ErbB receptor activation [ 305 ].…”

Therapeutic Role of Neuregulin 1 Type III in SOD1-Linked Amyotrophic Lateral Sclerosis

“…Importantly, loss-of-function mutations of NRG1 receptor ErbB4 cause a form of late-onset, autosomaldominant ALS in human patients [24]. Furthermore, we recently reported that ErbB4 ectodomain fragments were reduced in cerebrospinal fluid and plasma of ALS patients, indicating an impairment of the NRG1-ErbB signaling [25]. Also, in SOD1 G93A mice and in ALS patients, spinal cord microglial cells express the activated form of ErbB2 receptor and there are enhanced levels of NRG1 in microglial cells [23].…”