
Susana Gonzalo, Ph.D.
Associate Professor
Nuclear architecture, chromatin structure, and genomic instability in aging and cancer.
Research Interests
The human genome is organized into different levels of complexity. Packaging of DNA into different chromatin states and 3D nuclear organization of the genome are emerging as additional levels of regulation of genome function and integrity.
Our broad research interests aim to understand how alterations of nuclear architecture contribute to the genomic instability that drives aging and cancer processes. Our studies are revealing essential roles for the structural nuclear protein A-type lamins in DNA repair, DNA replication, and telomere homeostasis, as well as in genome compartmentalization and mobility within the nuclear space. These findings, and the association of lamins dysfunction with degenerative disorders, premature aging, and cancer, provide evidence for lamins operating as “caretakers of the genome.”
We are currently focusing on molecular mechanisms of genomic instability in Hutchinson Gilford Progeria Syndrome (HGPS), a premature aging laminopathy, and cancers with the poorest prognosis, such as BRCA-mutated and triple negative breast cancers (TNBC). Intriguingly, we find similar alterations in cells from these aggressive cancers and in cells from HGPS patients, including deficiencies in DNA repair/replication and in vitamin D/vitamin D receptor (VDR) signaling. Importantly, we discovered that calcitriol, the most bioactive vitamin D metabolite, greatly improves a variety of phenotypes in cells from breast cancer and HGPS patients.
Our long-term goal is to characterize how these pathways contribute to disease in cells in vitro and in animal models in vivo, as well as their potential as targets for treatment of lamins-related diseases.
Recent Publications
Pushing the limit on laminopathies
Calcitriol Prevents RAD51 Loss and cGAS-STING-IFN Response Triggered by Progerin
Calcitriol Prevents RAD51 Loss and cGAS-STING-IFN Response Triggered by Progerin
Hutchinson Gilford progeria syndrome (HGPS) is a devastating accelerated aging disease caused by LMNA gene mutation. The truncated lamin A protein produced “progerin” has a dominant toxic effect in cells, causing disruption of nuclear architecture and chromatin structure, genomic instability, gene expression changes, oxidative stress, and premature senescence. It was previously shown that progerin-induced genomic instability involves replication stress (RS), characterized by replication fork stalling and nuclease-mediated degradation of stalled forks. RS is accompanied by activation of cGAS/STING cytosolic DNA sensing pathway and STAT1-regulated interferon (IFN)-like response. It is also found that calcitriol, the active hormonal form of vitamin D, rescues RS and represses the cGAS/STING/IFN cascade. Here, the mechanisms underlying RS in progerin-expressing cells and the rescue by calcitriol are explored. It is found that progerin elicits a marked downregulation of RAD51, concomitant with increased levels of phosphorylated-RPA, a marker of RS. Interestingly, calcitriol prevents RS and activation of the cGAS/STING/IFN response in part through maintenance of RAD51 levels in progerin-expressing cells. Thus, loss of RAD51 is one of the consequences of progerin expression that can contribute to RS and activation of the IFN response. Stabilization of RAD51 helps explain the beneficial effects of calcitriol in these processes.
Metabolic Dysfunction in Hutchinson-Gilford Progeria Syndrome
Metabolic Dysfunction in Hutchinson-Gilford Progeria Syndrome
Hutchinson-Gilford Progeria Syndrome (HGPS) is a segmental premature aging disease causing patient death by early teenage years from cardiovascular dysfunction. Although HGPS does not totally recapitulate normal aging, it does harbor many similarities to the normal aging process, with patients also developing cardiovascular disease, alopecia, bone and joint abnormalities, and adipose changes. It is unsurprising, then, that as physicians and scientists have searched for treatments for HGPS, they have targeted many pathways known to be involved in normal aging, including inflammation, DNA damage, epigenetic changes, and stem cell exhaustion. Although less studied at a mechanistic level, severe metabolic problems are observed in HGPS patients. Interestingly, new research in animal models of HGPS has demonstrated impressive lifespan improvements secondary to metabolic interventions. As such, further understanding metabolism, its contribution to HGPS, and its therapeutic potential has far-reaching ramifications for this disease still lacking a robust treatment strategy.
Lamin A/C promotes DNA base excision repair
Lamin A/C promotes DNA base excision repair
The A-type lamins (lamin A/C), encoded by the LMNA gene, are important structural components of the nuclear lamina. LMNA mutations lead to degenerative disorders known as laminopathies, including the premature aging disease Hutchinson-Gilford progeria syndrome. In addition, altered lamin A/C expression is found in various cancers. Reports indicate that lamin A/C plays a role in DNA double strand break repair, but a role in DNA base excision repair (BER) has not been described. We provide evidence for reduced BER efficiency in lamin A/C-depleted cells (Lmna null MEFs and lamin A/C-knockdown U2OS). The mechanism involves impairment of the APE1 and POLβ BER activities, partly effectuated by associated reduction in poly-ADP-ribose chain formation. Also, Lmna null MEFs displayed reduced expression of several core BER enzymes (PARP1, LIG3 and POLβ). Absence of Lmna led to accumulation of 8-oxoguanine (8-oxoG) lesions, and to an increased frequency of substitution mutations induced by chronic oxidative stress including GC>TA transversions (a fingerprint of 8-oxoG:A mismatches). Collectively, our results provide novel insights into the functional interplay between the nuclear lamina and cellular defenses against oxidative DNA damage, with implications for cancer and aging.
Genomic instability and innate immune responses to self-DNA in progeria
Genomic instability and innate immune responses to self-DNA in progeria
In the last decade, we have seen increasing evidence of the importance of structural nuclear proteins such as lamins in nuclear architecture and compartmentalization of genome function and in the maintenance of mechanical stability and genome integrity. With over 400 mutations identified in the LMNA gene (encoding for A-type lamins) associated with more than ten distinct degenerative disorders, the role of lamins as genome caretakers and the contribution of lamins dysfunction to disease are unarguable. However, the molecular mechanisms whereby lamins mutations cause pathologies remain less understood. Here, we review pathways and mechanisms recently identified as playing a role in the pathophysiology of laminopathies, with special emphasis in Hutchinson Gilford Progeria Syndrome (HGPS). This devastating incurable accelerated aging disease is caused by a silent mutation in the LMNA gene that generates a truncated lamin A protein “progerin” that exerts profound cellular toxicity and organismal decline. Patients usually die in their teens due to cardiovascular complications such as myocardial infarction or stroke. To date, there are no efficient therapies that ameliorate disease progression, stressing the need to understand molecularly disease mechanisms that can be targeted therapeutically. We will summarize data supporting that replication stress is a major cause of genomic instability in laminopathies, which contributes to the activation of innate immune responses to self-DNA that in turn accelerate the aging process.