DNAJB6 isoform specific knockdown: Therapeutic potential for limb girdle muscular dystrophy D1

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Limb girdle muscular dystrophy (LGMD) D1 is caused by dominant mutations in DNAJB6, a co-chaperone of heat shock protein 70 (HSP70).
• Two DNAJB6 isoforms, DNAJB6a and DNAJB6b, exist with distinct muscle localizations, and DNAJB6b is implicated in disease pathogenesis.
• Current treatment strategies are limited, and complete DNAJB6 knockout is not viable due to embryonic lethality.

Purpose of the Study:

• To develop and assess an isoform-specific knockdown approach for DNAJB6 using morpholinos.
• To investigate the therapeutic potential of selectively reducing DNAJB6b levels in LGMD D1.
• To analyze the proteomic changes associated with LGMD D1 and the effects of DNAJB6b reduction.

Main Methods:

• Developed morpholino-based, isoform-specific knockdown of DNAJB6a and DNAJB6b.
• Achieved selective reduction *in vitro* in mouse myotubes and human LGMDD1 myoblasts, and *in vivo* in mouse skeletal muscle.
• Utilized mass spectrometry to identify LGMDD1 protein signatures and assess proteomic changes after DNAJB6b knockdown in a knockin mouse model.

Main Results:

• Successfully demonstrated selective knockdown of DNAJB6a and DNAJB6b *in vitro* and *in vivo*.
• Identified an LGMDD1 protein signature related to protein homeostasis and myofibril structure.
• Selective reduction of DNAJB6b in LGMDD1 myotubes partially reversed the proteomic disease signature towards wild-type levels.

Conclusions:

• Isoform-specific knockdown of DNAJB6b is achievable and shows potential for correcting LGMDD1-associated proteomic alterations.
• Further *in vivo* functional studies are necessary to validate selective DNAJB6b reduction as a viable therapeutic strategy for LGMD D1.