Muscle targeting complexes and uses thereof for modulation of genes associated with muscle health

A complex comprising an anti-transferrin receptor 1 antibody covalently linked to a molecular payload that modulates the expression or activity of myostatin (MSTN), inhibin beta A (INHBA), activin receptor type-1B (ACVR1B), myosin light chain kinase (MLCK1), activin A receptor type-1 (ACVR1), atrogin-1 (FBXO32), tripartite motif containing 63 (TRIM63), myocyte-specific enhancer factor 2D (MEF2D), Krüppel-like factor 15 (KLF15), Mediator complex subunit 1 (MED1), Mediator complex subunit 13 (MED13), and/or protein phosphatase 1 regulatory subunit 3A (PPP1R3A), wherein the antibody comprises a heavy chain complementarity determining region 1 (CDR-H1) as set forth in SEQ ID NO:

• 51, a heavy chain complementarity determining region 2 (CDR-H2) as set forth in SEQ ID NO:
• 52, a heavy chain complementarity determining region 3 (CDR-H3) as set forth in SEQ ID NO:
• 53, a light chain complementarity determining region 1 (CDR-L1) as set forth in SEQ ID NO:
• 54, a light chain complementarity determining region 2 (CDR-L2) as set forth in SEQ ID NO:
• 55, and a light chain complementarity determining region 3 (CDR-L3) as set forth in SEQ ID NO:
• 50.