p62 is required to retain short-term repopulating and myeloid progenitor cells through inhibition of IKK/NF-κB/Ccl4 signaling at the bone marrow macrophage-osteoblast niche

In the bone marrow (BM), hematopoietic progenitors (HP) reside in specific anatomical niches near osteoblasts (Ob), macrophages (MΦ) and other cells forming the BM microenvironment. A connection between immunosurveillance and traffic of HP has been demonstrated but the regulatory signals that instruct immune regulation on HP circulation are unknown. We discovered that the BM microenvironment deficiency of p62, an autophagy regulator and signal organizer, results in loss of autophagic repression of macrophage contact-dependent activation of Ob NF-κB signaling. Consequently, Ob p62-deficient mice lose bone, Ob Ccl4 expression and HP chemotaxis towards Cxcl12 resulting in egress of short-term hematopoietic stem cells and myeloid progenitors. Finally, Ccl4 expression and myeloid progenitor egress are reversed by the deficiency of the p62 PB1 binding partner Nbr1. A functional ‘MΦ-Ob niche’ is required for myeloid progenitor/short-term stem cell retention, in which Ob p62 is required to maintain NF-κB signaling repression, osteogenesis and BM progenitor retention.