Hutchinson-Gilford Progeria Paves The Way For Novel Targeted Anti-aging Therapies

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Hutchinson-Gilford Progeria is an accelerated aging syndrome caused by a permanently farnesylated mutant lamin A, termed progerin. Recently, the FDA approved Lonafarnib, a farnesyltransferase inhibitor, to treat progeria, while Koblan and colleagues used novel gene editing methods to target the root cause of this disease by correcting the LMNA mutation.

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Hutchinson-Gilford Progeria (HGPS) is an accelerated aging syndrome characterized by alopecia, bioflavonoids skin atrophy, aberrant pigmentation, lipodystrophy, and death at a mean age of 14.3 resulting from heart failure. Progeria is caused by a mutation in the LMNA gene. Lamin A undergoes multiple posttranslational modifications, including the addition of a farnesyl isoprenoid lipid moiety to its C-terminal CaaXmotif by a farnesyltransferase that tethers it to the nuclear membrane. This step is followed by cleavage of the terminal 3 amino acids by the metalloprotease ZMPSTE24 and carboxymethylation of the C terminus by the isoprenylcysteine carboxymethyltrans-ferase. Finally, the 15 C-terminal amino acids, including the farnesyl tail, are cleaved by ZMPSTE24, releasing mature lamin A into the lamina.

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HGPS is caused by a de novo heterozygous point mutation in LMNA (c.1824 C>T; p.G608G) thereby activating a cryptic splice site and deleting 50 amino acids including the ZMPSTE24 cleavage site.'' Thus, patients accumulate a truncated and permanently farnesylated mutant lamin A, termed progerin. buy cistanche Progerin remains anchored to the nuclear membrane and disrupts nuclear scaffolding in a dominant manner, resulting in nuclear abnormalities, heterochromatin loss, telomeric DNA damage, and senescence.3

The intense investigation led to some promising therapeutic strategies to treat progeria. These include repair of the LMNA mutation by CRISPR-based gene editing, oligonucleotide-based approaches to prevent aberrant splicing of the pre-mRNA, drugs that increase progerin clearance, and interventions that target downstream consequences of progerin expression (e.g., telomeric DNA damage and senescence).

Here, we discuss two recent breakthroughs that offer exciting opportunities for the treatment of progeria. In November 2020, the Food and Drug Administration (FDA) approved Lona-farnib (Zokinvy), a farnesyltransferase inhibitor(FTI), for the treatment of progeria, while David Liu's group used adenine base editors (ABE) to correct the progeric C>T mutation.5

The permanent farnesylation and mem-brane tethering of progerin provided the rationale to test FTIs as potential in-terventions for progeria. A number of proteins, including small GTPases and tyrosine phosphatases, are farnesylated, and protein prenylation is required for the transforming activity of Ras. Consequently, FTIs advanced into clinical trials to treat malignancies, and it was deemed reasonable to explore their therapeutic potential in progeria.

FTI treatment improved the shape of HGPS nuclei and ameliorated pheno-types in progeroid mice.6 These findings laid the foundation for two single-arm clinical trials using Lonafarnib, a drug that inhibits farnesyltransferase. In 2007,62 HGPS patients from 34 different countries between 2-17 years of age were enrolled. Treatment with FTl improved weight gain and bone mineral density reduced vascular stiffness and increased survival by 2.5 years.78 Based on these results, the FDA granted the application Priority Review status, and Lo-nafarnib was designated a breakthrough therapy and Orphan Drug. Lonafarnib received FDA approval in November 2020 and is the first drug to treat progeria.

Although the trial results are encouraging, Lonafarnib treatment is not a cure for progeria. FTIs target a number of other proteins, which may result in long-term adverse effects. In addition, experiments in mice suggested that progerin, in the presence of FTI, may undergo geranylgeranylation. Thus, a combination of geranylgeranyl transferase 1 inhibitors in conjunction with drugs that target the biosynthetic pathway of farnesyl pyrophosphates, such as Zoledronic Acid (bisphosphonate) and Pravastatin, may further reduce protein prenylation. cistanch Nonetheless, improvement may be limited, as an expression of non-farnesylatable progerin in a mouse model still resulted in a——although milder——disease pheno-type." This highlights the importance of understanding the precise mechanism(s) by which progerin impairs cell physiology and to what extent blocking protein prenylation impacts it. Moreover, it is important to develop therapeutic agents that target the root cause of the problem: the LMNA mutation.

Enter genome editing

CRISPR-Cas9-mediated disruption of mutated LMNA previously resulted in improved phenotypes in HGPS fibroblasts and mouse models.4 However, these approaches have limited translational potential as they generated deletions and insertions. To circumvent this problem, laboratory-evolved ABEs were fused to a catalytically dead CRISPR-Cas nuclease and guided to the LMNA locus by a guide RNA. The ABE converted the mutated adenine (c.1824 C>T) to inosine, which pairs like guanine, restoring the complementary thymine back to cytosine (c.1824 T>C). cistanche Australia In HGPS fibroblasts, ABE-mediated correction of mutated LMNA occurred at high efficiency (~90%) and resulted in reduced progerin levels and restored nuclear morphology.

To test the ABCs in vivo, adeno-associated virus9(AAV9)capsids were used to deliver the ABCs to mice carrying the human LMNA G608G mutation. Injections were conducted at postnatal day 3 (P3) and P14 and the correction frequency was assessed 6 weeks and 6 months post-injection. Correction frequencies ranged from 10%-30% in the heart, quad, aorta, and bone to over 60% in the liver. Editing was less efficient in the lung, skin, visceral fat and white adipose tissue, kidneys, and spleen. Interestingly, the amount of corrected LMNA increased in a variety of tissues over time. This may be attributed to AAVs persisting in some tissues and continuing the editing process or edited cells exhibiting a growth advantage over uncorrected cells. In agreement with this notion, progerin levels declined significantly in the liver (-87%), heart (-86%), and aorta (-49%). Cardiovascular complications in HGPS patients are characterized by loss of vascular smooth muscle cells (VSMC), periadventitial thickening, and aortic stiffening. cistanche benefits Importantly, aortas from treated mice showed an 11-fold increase in VSMC, restored adventitial thickening and treated mice exhibited a 2.4-fold increased lifespan.

However, some aged, treated mice developed liver tumors that may have originated from an AAV insertion, associated with liver tumorigenesis. Additional studies will be necessary to determine the long-term consequences of AAV transduction and ABE treatment. Lastly, the introduction of ABCs into humans may elicit an immune response that needs to be monitored and possibly mitigated by immunosuppression.

Regardless, these spectacular results demonstrate that a single injection of ABE improved cardiac health, the key determinant of early morbidity in progeria patients, and extended the lifespan of progeroid mice. ABEs in conjunction with antisense oligonucleotides and FTI treatment create exciting new avenues for the treatment of HGPS and provide a proof of concept for other genetic conditions.

ACKNOWLEDGMENTS

This work was supported by the Singapore Biomedical Research Council and the Singapore Agency for Science, Technology and Research (A*STAR).

This article is extracted from Med 2, 353–354, April 9, 2021 ª 2021 Elsevier Inc.