Molecular insights into Hutchinson-Gilford progeria syndrome and age-associated disease : from mechanisms to treatment strategy

Aging is a complex process that occurs as we grow old and is associated with a gradual decline of tissue functions. Scientists have been trying to understand the mechanisms that drive such phenomenon by studying premature aging syndromes and aging-related disorders. The Hutchinson- Gilford progeria syndrome (HGPS) is a lethal segmental genetic disease affecting children at an early age and characterized by accelerated aging-like features including alopecia, loss of subcutaneous adipose tissue and cardiovascular pathologies. This disorder primarily results from the production of a noxious protein called progerin, altering proper tissue homeostasis and functions. Strikingly, HGPS children present an accelerated vascular aging phenotype similar to that of chronic kidney disease (CKD) patients. Indeed, in addition to displaying kidney defects, CKD patients exhibit an accelerated vascular decline. Interestingly, progerin has previously been found expressed in cells and tissues from aged individuals, but its contribution to aging and aging-associated disorders remains poorly understood. Here, we investigated whether and how various levels of progerin are relevant to the development and progression of tissue pathology in HGPS, normal aging and aging-associated diseases, in order to generate a potential new treatment strategy for HGPS in particular. In paper I, to better understand the mechanisms by which progerin accumulation disrupts tissue homeostasis, a humanized HGPS mouse model with overexpression of progerin in the skin was used. We demonstrated that progerin accumulation resulted in impaired tissue homeostasis as a consequence of an aberrant increase in symmetric cell division. Further analysis suggested a potential causal role of the Wnt/β-catenin signaling, associated with mislocalization of the nuclear envelope proteins emerin and nesprin-2. In paper II, to investigate whether a small fraction of progerin-expressing cells in a tissue can lead to tissue pathology during aging, another humanized HGPS mouse model was employed. We showed that continuous expression of progerin in only a few preadipocytes and adipocytes is associated with fibrosis and lipoatrophy over time. This phenotype was combined with increased senescence, persistent DNA damage and cell death, which were found accompanied by macrophage infiltration and systemic inflammation. These results suggested that progerin, despite being expressed in only a low fraction of the cells of a tissue, has the potential to contribute to a common aging-associated phenotype. In paper III, to unravel the possible involvement of progerin expression in age-associated diseases, we used arterial biopsies and blood from CKD patients. We found that progerin was expressed at low frequencies in 70% of the CKD patients arteries (in up to 7.4% of the cells), which was associated with an increase in DNA damage. When searching for the cause of progerin expression, we identified the LMNA c.1824C>T mutation in both the blood and arteries. Our data further suggested that progerinexpressing cells might arise during vascular regeneration, by proliferation of progenitor cells. In paper IV, to examine the mechanisms associated with telomere dysfunction in HGPS, we employed various in vitro systems and a severe progeroid mouse model of skin. We demonstrated that telomere dysfunction leads to the production of non-coding RNAs, which activates the DNA damage response signaling. Treatment with telomeric sequence-specific antisense oligonucleotides not only repressed this signaling, but also significantly improved both the healthspan and lifespan of HGPS mice. This thesis provides novel findings about the complex molecular mechanisms underlying progerin expression in HGPS, and its possible contribution to aging and CKD-related early vascular aging, all of which led to the discovery of a potential new treatment approach for HGPS

Inhibition of DNA damage response at telomeres improves the detrimental phenotypes of Hutchinson–Gilford Progeria Syndrome

Hutchinson–Gilford progeria syndrome (HGPS) is a genetic disorder characterized by premature aging features. Cells from HGPS patients express progerin, a truncated form of Lamin A, which perturbs cellular homeostasis leading to nuclear shape alterations, genome instability, heterochromatin loss, telomere dysfunction and premature entry into cellular senescence. Recently, we reported that telomere dysfunction induces the transcription of telomeric non-coding RNAs (tncRNAs) which control the DNA damage response (DDR) at dysfunctional telomeres. Here we show that progerin-induced telomere dysfunction induces the transcription of tncRNAs. Their functional inhibition by sequence-specific telomeric antisense oligonucleotides (tASOs) prevents full DDR activation and premature cellular senescence in various HGPS cell systems, including HGPS patient fibroblasts. We also show in vivo that tASO treatment significantly enhances skin homeostasis and lifespan in a transgenic HGPS mouse model. In summary, our results demonstrate an important role for telomeric DDR activation in HGPS progeroid detrimental phenotypes in vitro and in vivo

The Heterochromatin protein 1 is a master regulator in RNA splicing precision deficient in ulcerative colitis

Defects in RNA splicing have been linked to numerous human disorders, but remain poorly explored in inflammatory bowel disease (IBD). Here, we report that, in the gut epithelium of patients with ulcerative colitis (UC), the expression of the chromatin and alternative splicing regulator HP1γ is strongly reduced. Accordingly, inactivation of the HP1γ gene in the mouse gut triggered several IBD-like traits, including inflammation and dysbiosis. In parallel, we discovered that its loss of function broadly increased splicing noise, reducing requirement for canonical splicing consensus sequences, and favoring the usage of cryptic splice sites at numerous genes with key functions in gut biology. This notably resulted in the production of progerin, a noncanonical toxic splice variant of prelamin A mRNA, responsible for the Hutchinson Gilford Progeria Syndrome (HGPS) of premature aging. Likewise, production of progerin transcript was found to be a signature of colonic cells from UC patients. Thus, our study identifies HP1γ as a regulator of RNA metabolism in vivo , providing a unique mechanism linking anti-inflammation and accuracy of RNA splicing in the gut epithelium. HP1 defect may confer a general disturbance in RNA splicing precision to scrutinize in IBD and more generally in accelerating aging diseases