OSBPL7

OSBPL7/ORP7 is a sterol-binding protein of the oxysterol-binding protein family that links sterol sensing to membrane traffic, autophagy-related machinery, and cholesterol efflux (PMID:17428193, PMID:21669198, PMID:34341345). It binds 25-hydroxycholesterol through a conserved pocket in its C-terminal OSBP-related ligand-binding domain (ORD), while its N-terminal PH-domain region confers plasma membrane targeting; the protein partitions between cytosol, ER membranes, and a minor plasma membrane pool (PMID:17428193, PMID:14593528). ORP7 interacts with the autophagy-related SNARE-modifier GATE-16 (GABARAPL2) via its N-terminal region, and this interaction drives proteasomal destabilization of the Golgi SNARE GS28; 25-hydroxycholesterol potentiates this effect, and ORP7 overexpression promotes association with LC3-positive autophagosomal structures, coupling sterol ligand status to SNARE turnover (PMID:21669198). OSBPL7 is the direct molecular target of 5-arylnicotinamide compounds that upregulate ABCA1- and ABCG1-dependent cholesterol efflux, and it interacts with AKT1; pharmacological engagement induces cholesterol efflux from podocytes and endothelial cells, while its inhibition perturbs cellular lipid composition and angiogenesis (PMID:34341345, PMID:39695567). Functionally, OSBPL7 deficiency triggers ER stress-mediated podocyte apoptosis, proteinuria, and elevated cellular triglyceride, establishing a role in podocyte and glomerular integrity (PMID:34341345, PMID:38961844).

1. 2003 Medium

   Established where ORP7 acts in the cell and which domain directs its localization, framing it as a membrane-associated protein with PH-domain-driven plasma membrane targeting.

   Evidence Subcellular fractionation and truncation-construct expression/immunolocalization in cultured cells

   PMID:14593528

   Open questions at the time

   • The phosphoinositide or lipid recognized by the PH domain is not defined
   • Functional consequence of the ER versus plasma membrane pools is unresolved
2. 2007 High

   Defined the molecular ligand of ORP7, showing its ORD binds 25-hydroxycholesterol through a conserved pocket and establishing it as a bona fide sterol-binding protein.

   Evidence In vitro [3H]25-hydroxycholesterol binding with recombinant protein plus live-cell photo-cross-linking in COS7 cells

   PMID:17428193

   Open questions at the time

   • Whether sterol binding gates a transport or signaling activity was not addressed
   • No structural model of the bound pocket
3. 2011 High

   Connected ORP7's sterol-sensing to membrane-traffic machinery by identifying GATE-16 as a partner and GS28 as a destabilized SNARE, with 25-hydroxycholesterol potentiating the effect.

   Evidence Yeast two-hybrid, BiFC, siRNA/overexpression with domain-mapping, immunoblotting, and RFP-LC3 imaging in 293A cells

   PMID:21669198

   Open questions at the time

   • Direct ubiquitin-ligase or proteasome-targeting mechanism for GS28 not identified
   • Physiological consequence of GS28 turnover not established in vivo
4. 2021 High

   Identified OSBPL7 as the direct druggable target of cholesterol-efflux-inducing compounds, linking it causally to ABCA1-dependent efflux and therapeutic correction of proteinuria.

   Evidence Photoactivatable compound cross-linking/IP target-ID, cholesterol efflux assays, and Adriamycin/Alport mouse models

   PMID:34341345

   Open questions at the time

   • Molecular mechanism by which OSBPL7 represses ABCA1 expression is undefined
   • Whether sterol binding mediates the efflux regulation is not shown
5. 2024 Medium

   Placed ER stress-mediated apoptosis as the primary injury pathway in OSBPL7-deficient podocytes, distinguishing it from autophagic or lipid-dysmetabolism mechanisms.

   Evidence siRNA knockdown in podocytes, mouse CKD models, zebrafish morpholino knockdown, ER stress/apoptosis markers and lipid quantification

   PMID:38961844

   Open questions at the time

   • How OSBPL7 loss triggers ER stress mechanistically is unknown
   • Morpholino-based zebrafish phenotype awaits genetic confirmation
6. 2024 Medium

   Extended OSBPL7 function to endothelial cholesterol efflux and angiogenesis and identified AKT1 as an interaction partner, broadening its lipid-handling and signaling roles.

   Evidence BioID proximity interactomics, lipidomics, transcriptomics, cholesterol efflux and tube-formation assays in primary HUVECs

   PMID:39695567

   Open questions at the time

   • AKT1 interaction not validated by an orthogonal method
   • Functional significance of the OSBPL7-AKT1 association is not defined

• It remains unresolved how sterol binding mechanistically couples to OSBPL7's regulation of SNARE turnover, ABCA1/ABCG1-dependent efflux, and ER stress signaling within a unified model.
• No structure of the full-length protein or its complexes
• Whether sterol transfer activity exists is undemonstrated
• Direct molecular link between OSBPL7 and ABCA1/ABCG1 transcription not established