2022 Volume 29 Issue 4 Pages 439-447
Hutchinson–Gilford progeria syndrome (HGPS) and Werner syndrome (WS) are two of the representative genetic progeroid syndromes and have been widely studied in the field of aging research. HGPS is a pediatric disease in which premature aging symptoms appear in early childhood, and death occurs at an average age of 14.5 years, mainly due to cardiovascular disease (CVD). Conversely, WS patients exhibit accelerated aging phenotypes after puberty and die in their 50s due to CVD and malignant tumors. Both diseases are models of human aging, leading to a better understanding of the aging-associated development of CVD. In this review, we discuss the pathogenesis and treatment of atherosclerotic diseases presented by both progeroid syndromes with the latest findings.
In 2020, the world’s population aged 65 or older was 727 million. Over the next 30 years, the number of older people worldwide will be more than double and is projected to exceed 1.5 billion by 2050 1) . Aging is an independent risk factor for the development of cardiovascular diseases (CVDs) and is considered to be the greatest risk 2, 3) . Therefore, the research focused on the mechanism underlying aging-associated CVD development is essential.
Progeroid syndrome represented by Hutchinson–Gilford progeria syndrome (HGPS) and Werner syndrome (WS) has been studied as a model disease of human aging because aging-like symptoms appear from a young age and their pathological condition mimics general aging. These premature aging syndromes also display the early onset of CVD. This paper outlines the clinical features and molecular mechanisms of the two aforementioned syndromes, focusing on atherosclerotic diseases, with the latest findings.
HGPS is an ultra-rare autosomal dominant genetic premature aging syndrome that occurs in one in four to eight million births and causes death at an average age of 14.5 years due to myocardial infarction or stroke 4, 5) ( Table 1) . Because of the abnormal splicing of the LMNA gene on chromosome 1, the lamin A protein encoded by this gene cannot be normally produced, and an abnormal protein called progerin accumulates in the nucleus. The main symptoms are scleroderma-like skin, joint contractures, bone abnormalities, hair loss, growth retardation, and atherosclerotic diseases, such as myocardial infarction and stroke.
| HGPS | WS | |
|---|---|---|
| Disease prevalence | 1 in 20 million 5) | 9.0 in 1 million in Japan 87) , 1.0 to 2.7 in 1 million globally 47) |
| Ethnicity | Ubiquitous 7) | Relatively prevalent in Japanese and Sardinian 47) |
| Sex | Equally affected 7) | Equally affected 48) |
| Lifespan | Average 14.5 years 5) | Average 55.0 years 65) , median 54.3 years 88) |
| Responsible gene and frequent mutation | LMNA: c.1824C＞T (90% of patients) 5) | WRN: c.3139-1G＞C (70.7% of allele in Japanese patients), WRN: c.1105C＞T (18.6% of allele in non-Japanese patients) 47) |
| Diabetes or IGT | 15.4% of patients 6) | 67.5% of patients 67) |
| Dyslipidemia | 71.4% of patients 6) | 65.0 to 85.0% of patients 52, 67) |
| Hypertension | 46.7% of patients 6) | 42.5% of patients 67) |
| CVD | 100% had adventitial thickening in the carotid artery, 18.2% had the low ankle- brachial index 6) | 15% had ASO, 2.5% had AP or MI, none had cerebral artery disease 67) |
| Causes of death (percentage of total) |
Heart failure (80%), head injury (9%), complications of surgery (4%), stroke (3%) 7) |
Malignancy (56%), AMI (28%), infection (14%), cerebral bleeding (2%) 65) |
Abbreviations: IGT, impaired glucose tolerance; ASO, atherosclerosis obliterans; AP, angina pectoris; MI, myocardial infarction; AMI, acute myocardial infarction.
Infants with HGPS are normal at birth, but the mean weight is slightly small for gestational age 4) . The first pathognomonic signs are prominent veins on the nose bridge, followed by growth retardation, hair loss, and reduced subcutaneous fat around 6 to 12 months, and the diagnosis is often made between 2 and 3 years of age. Symptoms in the craniofacial region gradually appear, including alopecia, with only a few hairs, abnormally prominent scalp veins, larger skull than the facial bone, pseudo-protrusion of the eyes due to a decrease in surrounding adipose tissue, loss of subcutaneous fat and muscles in the face, a narrowing of the nose bridge and a hooked nose, wrinkles around the lips due to thinning of the skin, abnormal dentition, and caries, a small jaw, large ears lacking earlobes, and a high-pitched voice. Symptoms in the trunk and extremities include loss of subcutaneous fat and muscle mass, protruding joints and decreased range of motion, and hypertrophy of the tips of the fingers. On the other hand, there is no intellectual impairment or psychiatric symptoms, and most of the affected children are charming and active. The growth disturbance is remarkable, especially in weight, with most children over 12 years old weighing around 15 kg (same as 3- to 4-year-old healthy children). As a result, they gradually develop the appearance resembling older people.
In a report of 15 white patients (median age, 6 years and 11 months), the average body fat percentage was as low as 16% (below −1 SD) and tended to decrease with age 6) . Seven had higher blood pressure than healthy children of the same age and height, five had abnormal electrocardiograms, and three had echocardiographic abnormalities at rest. Carotid artery ultrasonography revealed adventitial thickening in all patients and stenosis and occlusion in three. In addition, the ankle-brachial index decreased in three patients. Although muscle strength was preserved, 11 patients had osteoporosis, and all 15 patients had osteolysis of the distal phalanges and clavicles, as seen on X-ray. Blood tests revealed a decreased level of high-density lipoprotein cholesterol in 10 patients. Glycated hemoglobin was in the normal range, but five had elevated fasting insulin levels, and one was diagnosed with diabetes via oral glucose tolerance test. The creatinine and urea nitrogen levels were in the normal range.
The cause of death is predominantly CVD 7) . CVD events do not occur until around the age of 5 years, but the children gradually suffer from dyspnea due to heart failure or ischemic heart disease and paralysis caused by stroke 4, 8) . Myocardial infarction and heart failure are frequent and account for 80% of deaths 4, 7) . Other reported causes of death include intracranial hemorrhage, seizures, infections, and complications from cardiovascular surgery 4, 7) .
In autopsy, the loss of vascular smooth muscle in the media is prominent 4, 9) . Calcification and plaque formation in the coronary arteries vary from patient to patient 4, 10) .
A study that assessed 27 HGPS patients reported that diastolic dysfunction was the most prevalent cardiac abnormality 11) . Other abnormalities, such as left ventricular (LV) hypertrophy, LV systolic dysfunction, and valve disease, were less common in those below 10 years old compared with teenagers 11) . These findings are consistent with general aging-associated heart failure, which is attributed to an impairment of the diastolic filling of the left ventricle, rather than a dysfunction of systolic function 12, 13) . A case report of a 14-year-old girl with HGPS described dilated cardiomyopathy with congestive heart failure 14) . Previous reports revealed that progerin is upregulated in human hearts with dilated cardiomyopathy 15, 16) , implying causal relationships between progerin expression and pathogenesis of cardiomyopathy.
Although it is believed that there is no difference in the disease incidence rate and phenotypes by race 7, 17) , there are relatively few reports from Asia and Africa. Four Japanese and nine Chinese cases were well described by Sato-Kawano et al. and Wang et al., respectively 18, 19) . Also, patients in Africa were reported by two case studies 20, 21) .
Lamin is a constituent of the lamina, an intermediate filament responsible for the lining structure of the nuclear envelope. There are three types of lamin, namely, lamin A, lamin B, and lamin C. They are involved in the regulation of DNA transcription, replication, repair, and signal transduction from the cytoskeleton to the nucleus by stabilizing the structure of the nuclear envelope and anchoring chromosomes and transcription factors to the nuclear envelope 22) . Diseases caused by lamin abnormalities include HGPS, muscular dystrophy, neuropathy, and atypical WS 23) , which are collectively called laminopathies.
Lamin A/C is translated via alternative splicing from LMNA, which is located on the long arm of chromosome 1 and consists of 12 exons 4) . First, prelamin A is translated from LMNA. Prelamin A has a CAAX motif (C, cysteine; A, aliphatic amino acid; X, any amino acid) at the C-terminal, which works as an indicator for farnesyltransferase to farnesylate the cysteine residue. Next, Zmpste24, a metalloprotease, cleaves AAX. Then, the remaining cysteine undergoes methylation by isoprenylcysteine carboxyl methyltransferase, and the C-terminal 15 amino acids are removed by Zmpste24 and other endoproteases to form mature lamin A.
A point mutation (c.1824C＞T, G608G, a silent mutation) has been found at codon 608 in the 11th exon of LMNA in almost all HGPS patients with classical symptoms. This results in an unusual splicing site and a loss of 50 amino acids, including the Zmpste24 recognition site, which leads to the production of progerin, an aberrant protein that remains farnesylated.
Progerin acts in a dominant-negative manner 24) . Due to the affinity of the farnesylated portion to the membrane, it remains bound to the nuclear membrane even during the M phase of the cell cycle, thus inhibiting normal mitosis 25) . Nuclear accumulation of progerin causes abnormal nuclear morphology, dysregulation of other gene expressions, disruption of DNA repair mechanisms, shortening of telomeres, genomic instability, and abnormal mitochondrial function, leading to premature cellular senescence 22) . It has also been reported that H3K9 methylation is reduced in HGPS cells as in normal aging 26) . Interestingly, it is also known that progerin accumulates in cells of healthy older people 27) , and this discovery has brought further attention to HGPS as a model disease of aging.
HGPS patients develop severe vascular changes, primarily vascular smooth muscle cell depletion, calcification, and fibrosis, in addition to electrical and functional abnormalities in the heart. Several HGPS animal models have been created to recapitulate and analyze these phenotypes 28) .
The most widely used animal model is the LmnaG609G mouse 29) . Similar to HGPS patients, this mouse harbors a silent mutation resulting in abnormal splicing and production of progerin; moreover, it has shortened life span and bone abnormalities. Villa-Bellosta et al. found that the aorta of LmnaG609G/ ＋ mice had excessive calcification and that there was insufficient production and extracellular accumulation of pyrophosphate, a major inhibitor of vascular calcification, in primary vascular smooth muscle cells of the aorta, leading to vascular calcification 30) .
On the other hand, LmnaG609G/G609G mice fed a high-fat diet do not develop atherosclerosis as observed in HGPS patients 31) . To address this issue, Hamczyk et al. generated Apoe−/− LmnaG609G/G609G mice and fed them with a high-fat diet 32) . They were able to develop atherosclerosis and recapitulate most of the cardiovascular phenotypes observed in HGPS patients.
The LmnaG609G mouse also reproduces the electrical phenotype in the heart. Macias et al. reported that cardiomyocytes from LmnaG609G mice show prolonged action potential duration and refractoriness after repolarization 33) , which may be related to the QT prolongation reported in some HGPS patients 6) .
Currently, there is no fundamental treatment for HGPS. However, the most encouraging recent topic is the FDA’s approval of lonafarnib, a drug that inhibits the farnesylation of lamin A 34, 35) . In an observational study with a median treatment duration of 2.2 years, 17 of 63 deaths occurred in the untreated group, compared with 4 of 63 deaths in the lonafarnib-treated group, with a hazard ratio of 0.23 7) . While lonafarnib improves cardiovascular phenotypes 36) , the addition of pravastatin and zoledronic acid has been found to be effective in treating musculoskeletal phenotypes 37, 38) .
CRISPR-based therapies are also in the limelight. Two reports of Lmna-targeted knockouts in LmnaG609G mice have observed prolonged lifespan, suppression of cardiac fibrosis, and improvement of vascular smooth muscle in the tunica media of the aortic arch 39, 40) . Interestingly, in both cases, the most efficiently genetically modified tissue was the liver, suggesting an association between hepatic dysfunction and the HGPS arteriosclerosis phenotype. In another report, mice carrying a mutation of a human HGPS patient (LMNAG608G ) were repaired with a base editor, which substitutes A-T to G-C at c.1824 in LMNA 41, 42) . Although the most genetically repaired tissue was the liver like the above two reports, vascular smooth muscle restoration and adventitial fibrosis suppression were observed. The base editor has been shown to restore angiogenic potential by reducing progerin expression and increasing intracellular nitric oxide levels in HGPS-induced pluripotent stem (iPS) cell-derived endothelial cells in vitro 43) .
Osorio et al. has reported that treatment of LmnaG609G mice with morpholino oligos to suppress aberrant splicing leads to an extended lifespan 29) . Recently, it was reported that suppression of abnormal splicing in transgenic mice carrying the human LMNAG608G mutation could also result in up to 61.6% lifespan extension and inhibition of vascular smooth muscle loss in large vessels 44, 45) . It is epoch-making in that gene therapy can be performed without editing patients’ DNA, and future clinical application is expected.
WS is an autosomal recessive progeroid syndrome, also known as adult progeria, due to the appearance of various premature aging symptoms in adulthood 46) ( Table 1) . The causative gene is WRN on the short arm of chromosome 8. About 70% of the cases reported to date are Japanese, and 1 in 150 normal Japanese people has a heterozygous mutation 47) . Patients with WS are generally short in stature but normally develop until puberty, and from around their 20s, they exhibit gray hair, hair loss, bird-like face, hoarseness, and scleroderma-like symptoms in the limbs 48) . Later, they develop cataracts, diabetes, osteoporosis, intractable skin ulcers, arteriosclerotic diseases, and malignant tumors (especially non-epithelial malignancy), and most of them die in their 50s.
One of the most important clinical features of the disease is intractable skin ulcers that occur mainly on the lower limbs, including the toes, heels, and Achilles tendons. In some cases, these ulcers lead to gangrene or osteomyelitis, leading to amputation of the lower extremities. Unlike foot ulcers of diabetes, WS ulcers are characterized by severe pain and subcutaneous calcification 49) , which significantly reduces the patient’s quality of life.
In addition, WS patients often accumulate visceral fat, resulting in diabetes and dyslipidemia based on insulin resistance 50) . On the other hand, because the limbs wither and atrophy like branches, patients’ body shapes are sometimes called Cushing-like appearance. The symptom of loss of muscle mass is called sarcopenia and has become a major topic in geriatrics. In a study of nine patients with WS, all of them met the diagnostic criteria for sarcopenia 51) .
The key signs to clinically suspect WS are the appearance of gray hair and hair loss (attention must be paid to hair dye and wigs) as well as bilateral cataracts under the age of 30. If multiple corn/callus and calcification of the Achilles tendon are observed, genetic testing should be conducted to confirm the diagnosis. Please refer to the “Management guideline for Werner syndrome 2020” series for the main strategy to treat each specific symptom 52- 59) .
The WRN protein encoded by the WRN gene is a member of the RecQ helicase family together with RecQ1, BLM, RecQ4, and RecQ5 and has DNA helicase activity (the ability to unwind a DNA duplex into a single strand) as well as DNA exonuclease activity 60) . So far, at least 83 mutations have been reported 47) , and several new mutations have been identified in our laboratory 61) . On the other hand, there is no clear correlation between mutation sites and clinical signs.
WRN has a variety of functions, including DNA replication and repair, telomere maintenance, and epigenetic regulation, such as heterochromatinization. Among them, many reports have confirmed the involvement of WRN in DNA double-strand break (DSB) repair. There are two main pathways in DSB repair, namely, non-homologous end joining (NHEJ) and homologous recombination, and the WRN protein is involved in both 62) . A recent report demonstrated that WRN proteins promote classical-NHEJ and inhibit alternative-NHEJ, leading to repair error suppression 63) .
In another study, Zhang et al. reported that the WRN protein is involved in the methylation of H3K9, a marker of heterochromatin 64) . This loss of methylation is also observed in a general aging process, suggesting that WS mimics the general aging from an epigenetic point of view.
In WS, accumulation of DNA mutations, shortening of telomeres, and abnormalities in histone methylation are assumed to be responsible for various pathological conditions. However, the causal relationship between these abnormalities at the molecular level and the pathological conditions remains to be elucidated, and further research is needed.
Atherosclerotic disease is the second leading cause of death in WS 65) . According to a 2012 report of Japanese patients, the prevalence of vascular disease in WS was 1.1% for cerebral hemorrhage, 2.7% for cerebral infarction, 10.3% for angina and myocardial infarction, and 17.3% for arteriosclerosis obliterans 66) . The latest report from the Japanese WS Registry revealed a decrease in the prevalence of 0%, 0%, 2.5%, and 15%, respectively 67) . In addition to the use of statins 68) , this reduction may be due to the remarkable development of antidiabetic drugs in recent years 67) . In fact, in some of the case reports of WS in recent years, no obvious atherosclerotic disease was found 69- 72) or was only slightly present 61, 73, 74) . In the case of a patient who died at 76 years of age, there were almost no findings of atherosclerosis in the cerebral arteries, and only calcification without stenosis was observed in the aorta and coronary arteries 75, 76) . In eight genetically diagnosed Chinese WS patients, the atherosclerotic disease was evident in only one patient 77) .
Dyslipidemia affects 65% to 85% of WS patients 52, 67) . Of those, the frequency of hypertriglyceridemia is somewhat higher. In fact, patients with hypertriglyceridemia accompanied by 3900 mg/dl of triglycerides had advanced three-vessel disease requiring coronary artery bypass surgery 78) . In addition to statins to hypercholesterolemia, adequate management of hypertriglyceridemia may also be required.
On the other hand, in some cases, severe aortic stenosis, without the requirement of coronary intervention, has become a problem 79, 80) . In addition, cases of heart failure due to impaired coronary microcirculation with no coronary artery stenosis have been reported 81) . These suggest that arteriosclerosis in WS needs to be comprehensively evaluated.
A mouse model of WS does not develop arteriosclerosis 82) . A report of knockdown of the WRN gene using human endothelial cells in vitro demonstrated increased expression of inflammation and adhesion molecules 83) . On the other hand, a report of differentiation of WRN knockout embryonic stem cells into endothelial cells described no phenotypic changes 84) . Understanding the molecular mechanisms of atherosclerosis in WS requires further investigation.
As aforementioned, HGPS and WS are representative diseases of premature aging, and patients suffer from shortened life expectancy and reduced quality of life. One reason for that is because the full picture of their underlying mechanisms is still unclear. Furthermore, we are globally encountering a super-aging society. The study of progeria is extremely significant as it will contribute to the elucidation of the mechanisms of a general aging. The registration of patients into the HGPS and WS registries both in Japan and overseas is currently ongoing, and we expect that the understanding of the natural history of the disease will elucidate the clinical problems that need to be addressed. In addition, analyses using primary patient samples and patient-derived iPS cells are underway, including in our laboratory, using state-of-the-art technologies, such as the genome, transcriptome, and epigenome analyses 85, 86) . These studies are expected to lead to breakthroughs in the treatment of progeria and the study of general aging.
This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI under Grant Numbers JP20K16542 (H.K.) and JP20H03572 (Y.M.).
The authors declare there are no conflicts of interest related to this work.
