A prospective study on myofiber contractility in myositis

Myositis is an auto-immune disease affecting around 100.000 people in Europe.
Patients suffer from severe muscle weakness and inflammation, heavily impacting
daily activities and quality of life. Up to half of the patients develop
pulmonary and cardiac conditions due to chronic multi-organ inflammation. The
need for improved, patient-centered therapies is evident as current treatments
are insufficient, cause side-effects and absence from work, and require
intensive intramural care.

A better understanding of the pathophysiology underlying muscle weakness is key
to identify contributors that should be targeted to prevent or revert this
defect in an early stage. Myositis specific autoantibodies (MSA) and
auto-immune pathways like interferon- and complement system cause direct muscle
damage, but patients also show impaired muscle fiber contraction with unknown
cause. Based on pilot data revealing reduced muscle fiber contractility in
myositis patients with MSA, a two-step approach is proposed to determine the
impact of MSA on muscle contractility:
1. Analyze human muscle fiber contractility from biopsies of patients with MSA
including effects of standard of care immunosuppressant therapy.
2. Establish an ex vivo model of mouse muscle fiber contractility, a unique
read-out for myositis based on muscular function. It enables screening for
patients* MSA that impair muscle fiber contractility and proprietary compounds
that restore this.

In this clinical project we aim to fill in gaps in our knowledge on muscle
fiber contractility, auto-immunity and myositis: 1) How responsive is human
muscle fiber contractility following standard of care immunosuppressive
treatment? 2) Is the severity of muscle fiber contractility impairment at
baseline and changes thereof over time, related to clinical outcomes? 3) To
what extent are muscle fiber contractility parameters associated with
established parameters derived from serum, electrophysiology (EMG) and imaging
(ultrasound, MRI).

Related to this and within the context of a translational approach, we aim to
examine the effects of constituents of myositis patients* sera (complete serum,
total IgGs and purified auto-antibodies) on murine muscle fiber contractility,
with the ambition to develop an ex-vivo model for studying MSA's and fiber
contractility. Together, we hope to establish a firm knowledge base on the
clinical correlates of muscle fiber contractility and to be able to further
develop an ex-vivo model for myositis.

Specific aims:
1. To determine the course of muscle fiber contractility in adult patients with
myositis with and without (known) myositis specific antibodies following
standard of care treatment.
2. To correlate muscle fiber contractility with established serum,
electrophysiological and imaging biomarkers
3. To collect blood samples for the investigation of the effect of human serum,
IgG and autoantibodies on murine myofiber contractility in the context of a
laboratory study.

prospective cohort study.

Aim 1 and 2:
Following a screening visit (week 0) at the outpatient clinic - which is
combined with a regular care visit, patients are included after informed
consent (IC). Patients will be assessed at baseline, treated with standard of
care immunosuppressive medication and they will be assessed at a follow-up
visit between 10 and 15 weeks after the baseline visit. Both study assessments,
visit 1 and 2, will be combined with a visit in the context of regular
outpatient care.

The burden of the study procedures is described below, per aim, because
participants can be included for the complete study (aim 1,2 and 3) or for only
a part of the study (aim 3).

The burden related to aims 1 and 2 consists of:
Week 0 (visit 1, baseline): Patients will complete the ALDS questionnaire and
additional 25 cc blood will be collected during a routine venipuncture.
Additionally, the following study procedures will be performed:
- extension of a routine MRI of the muscles (30 minutes longer)
- isometric knee extension strength assessment
- needle electromyography and an ultrasound of the muscles.
The first muscle biopsy is part standard care and is not a study procedure. A
part of the tissue will be used for contractility measurements. In small
proportion of the patients, an extra piece of tissue will be biopsied during
the regular procedure for RNA sequencing of inflammatory cells.

Follow-up 10 to 15 weeks: patients will complete the ALDS questionnaire and
additional 25 cc blood will be collected during a routine venipuncture. The
following study procedures will be performed:
- extension of a routine MRI of the muscles (30 minutes longer)
- isometric knee extension strength assessment - needle electromyography
- ultrasound of the muscles and a muscle biopsy.
- muscle biopsy (open or needle biopsy)

The burden related to aim 3 consists of: - 120 cc of blood (all for experiments
in murine myofibers), which will be collected during a routine venipuncture (as
described above).

The risks associated with this study, are mostly related to the complication
risk of the second biopsy; infection and bleeding. The risks are negligible.

As described in our protocol, inclusion for different parts of our research is
possible:
1. Complete study as described above (aim 1,2,3)
2. Serum/plasma collection (aim 3)
3. Serum/plasma collection and extension of MRI (partially aim 2 and 3).

The results of this studies may a) provide valuable information on the relation
between human muscle fiber contractility, auto-immunity and clinical outcomes,
and b) contribute to the development of a disease model based on human
MSA*s.