Earlier, we demonstrated that exon 4 deletion in the lipase H gene caused an ARH (hypotrichosis 7; MIM: 604379) in populations of the Volga-Ural region of Russia.
Mutations in 3 other associated genes, proprotein convertase subtilisin/kexin type 9, apolipoprotein B (APOB), and, more rarely, the autosomal recessive hypercholesterolemia adaptor protein, may lead to a similar phenotype with varying severity.
The ARH protein is involved in cell cycle progression, possibly by affecting nuclear membrane formation through interaction with lamin B1 or other mitotic proteins, and its absence affects cell proliferation and induces premature senescence, which may play a role in the development of atherosclerosis in ARH.
We showed that ARH contributes to several aspects of mitosis: it localizes to mitotic microtubules, with lamin B1 on the nuclear envelope and spindle matrix, and with clathrin heavy chain on mitotic spindles.
By sequential mutation and expression of a panel of amnionless mutants combined with yeast two-hybrid analyses, we demonstrate that the signals are functionally redundant and both are able to mediate endocytosis of cubam through interaction with Dab2 and ARH.
These results suggest defective activation of P2Y5 due to reduced 2-acyl lysophosphatidic acid production by the mutant PA-PLA(1)alpha is involved in the pathogenesis of ARH.
The translation of this mRNA yields a mutant protein product (ARH-26) lacking 26 amino acids, resulting in the loss of beta-strands beta6 and beta7 from the PTB domain.
The translation of this mRNA yields a mutant protein product (ARH-26) lacking 26 amino acids, resulting in the loss of beta-strands beta6 and beta7 from the PTB domain.
GST-pulldown experiments indicate that the phosphotyrosine binding domain of ARH interacts with the internalization sequence (NPVY) in the cytoplasmic tail of LDLR, and that conserved motifs in the C-terminal portion of the protein bind to clathrin and to the beta2-adaptin subunit of AP-2.
GST-pulldown experiments indicate that the phosphotyrosine binding domain of ARH interacts with the internalization sequence (NPVY) in the cytoplasmic tail of LDLR, and that conserved motifs in the C-terminal portion of the protein bind to clathrin and to the beta2-adaptin subunit of AP-2.
Our results also indicate that ARH1 carrier status is present in ∼1:2500 of Sicilian inhabitants, confirming that ARH is extremely rare outside Sardinia.
Nonresponse to PCSK9 inhibition was attributed to autosomal recessive hypercholesterolemia (secondary to low-density lipoprotein receptor adaptor protein 1 mutation) and plasmapheresis after PCSK9 inhibitor drug injections.
Overall, the effects of recombinant PCSK9, and hence of alirocumab, on LDL receptor expression and function were significantly less pronounced in ARH than in control cells.
Mutations in 3 other associated genes, proprotein convertase subtilisin/kexin type 9, apolipoprotein B (APOB), and, more rarely, the autosomal recessive hypercholesterolemia adaptor protein, may lead to a similar phenotype with varying severity.
LDLR activity was measured by flow cytometry, which showed that LDL binding and uptake were reduced in lymphocytes from the ARH patient as compared to control lymphocytes, but were slightly higher than in those from the LDLR:p.(Cys352Ser) heterozygote.
Overall, the effects of recombinant PCSK9, and hence of alirocumab, on LDL receptor expression and function were significantly less pronounced in ARH than in control cells.