The modular adaptor protein autosomal recessive hypercholesterolemia (ARH) promotes low density lipoprotein receptor...

Area of Science:

• Cell biology
• Molecular genetics
• Biochemistry

Background:

• Autosomal recessive hypercholesterolemia presents a cell-specific defect in low-density lipoprotein receptor (LDLR) endocytosis.
• This impairment in LDLR-mediated LDL uptake is observed in the liver but not in fibroblasts.

Purpose of the Study:

• To investigate the physiological relevance of ARH protein interactions with the LDLR and endocytic machinery.
• To determine the specific domains and interactions of ARH necessary for LDLR clustering and internalization.

Main Methods:

• Utilized polarized hepatocytes (WIF-B) to study the effect of ARH mutations on LDLR localization and function.
• Employed in vivo studies using Arh(-/-) mice and recombinant ARH to validate cell culture findings.

Main Results:

• The integrity of the FDNPVY sequence in the LDLR cytoplasmic tail is crucial for ARH-associated LDLR clustering into clathrin-coated pits.
• ARH's phosphotyrosine binding domain, along with its clathrin box or AP-2 binding region, is essential for LDLR clustering and internalization.
• In vivo studies in mice confirmed the necessity of these ARH interactions for LDLR function.

Conclusions:

• ARH protein acts as a critical adaptor, linking the LDLR to the clathrin-mediated endocytic pathway.
• Successful LDL internalization requires ARH to bind the LDLR tail and interact with either clathrin or AP-2.