Loss of caspase-2 accelerates age-dependent alterations in mitochondrial production of reactive oxygen species

Caspase-9 Is a Positive Regulator of Osteoblastic Cell Migration Identified by diaPASEF Proteomics

Caspase-9 is traditionally considered the initiator caspase of the intrinsic apoptotic pathway. In the past decade, however, other functions beyond initiation/execution of cell death have been described including cell type-dependent regulation of proliferation, differentiation/maturation, mitochondrial, and endosomal/lysosomal homeostasis. As previous studies revealed nonapoptotic functions of caspases in osteogenesis and bone homeostasis, this study was performed to identify proteins and pathways deregulated by knockout of caspase-9 in mouse MC3T3-E1 osteoblasts. Data-independent acquisition-parallel accumulation serial fragmentation (diaPASEF) proteomics was used to compare protein profiles of control and caspase-9 knockout cells. A total of 7669 protein groups were quantified, and 283 upregulated/141 downregulated protein groups were associated with the caspase-9 knockout phenotype. The deregulated proteins were mainly enriched for those associated with cell migration and motility and DNA replication/repair. Altered migration was confirmed in MC3T3-E1 cells with the genetic and pharmacological inhibition of caspase-9. ABHD2, an established regulator of cell migration, was identified as a possible substrate of caspase-9. We conclude that caspase-9 acts as a modulator of osteoblastic MC3T3-E1 cell migration and, therefore, may be involved in bone remodeling and fracture repair.

Impact of aging on primary liver cancer: epidemiology, pathogenesis and therapeutics

Aging involves progressive physiological and metabolic reprogramming to adapt to gradual deterioration of organs and functions. This includes mechanisms of defense against pre-malignant transformations. Thus, certain tumors are more prone to appear in elderly patients. This is the case of the two most frequent types of primary liver cancer, i.e., hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA). Accordingly, aging hallmarks, such as genomic instability, telomere attrition, epigenetic alterations, altered proteostasis, mitochondrial dysfunction, cellular senescence, exhaustion of stem cell niches, impaired intracellular communication, and deregulated nutrient sensing can play an important role in liver carcinogenesis in the elders. In addition, increased liver fragility determines a worse response to risk factors, which more frequently affect the aged population. This, together with the difficulty to carry out an early detection of HCC and iCCA, accounts for the late diagnosis of these tumors, which usually occurs in patients with approximately 60 and 70 years, respectively. Furthermore, there has been a considerable controversy on what treatment should be used in the management of HCC and iCCA in elderly patients. The consensus reached by numerous studies that have investigated the feasibility and safety of different curative and palliative therapeutic approaches in elders with liver tumors is that advanced age itself is not a contraindication for specific treatments, although the frequent presence of comorbidities in these individuals should be taken into consideration for their management.

Caspase-2 as a master regulator of genomic stability

Genomic instability underlies genesis and the development of various types of cancer. During tumorigenesis, cancer initiating cells assume a set of features, which allow them to survive and proliferate. Different mutations and chromosomal alterations promote a selection of the most aggressive cancer clones that worsen the prognosis of the disease. Despite that caspase-2 was described as a protease fulfilling an initiator and an effector function in apoptosis, it has recently been discovered to play an important role in the maintenance of genomic integrity and normal chromosome configuration. This protein is able to stabilize p53 and affect the level of transcription factors, which activates cell response to oxidative stress. Here we focus on the discussion on the mechanism(s) of how caspase-2 regulates genomic stability and decreases tumorigenesis.

Aging and calorie restriction regulate the expression of miR-125a-5p and its target genes Stat3, Casp2 and Stard13

Calorie restriction (CR) is a dietary intervention known to delay aging. In order, to understand molecular mechanisms of CR, we analyzed the expression of 983 MicroRNAs (miRNAs) in the liver of female mice after 2 years of 30% CR using micro-array. 16 miRNAs demonstrated significant changes in their expression upon CR in comparison with age-matched control. mmu-miR-125a-5p (miR-125a-5p) was significantly upregulated upon CR, and in agreement with this, the expression of mRNAs for its three predicted target genes: Stat3, Casp2, and Stard13 was significantly downregulated in the liver of CR animals. The expression of precursor miRNA for miR-125a-5p was also upregulated upon CR, which suggests its regulation at the level of transcription. Upon aging miR-125a-5p expression was downregulated while the expression of its target genes was upregulated. Thus, CR prevented age-associated changes in the expression of miR-125a-5p and its targets. We propose that miR-125a-5p dependent downregulation of Stat3, Casp2, and Stard13 contributes to the calorie restriction-mediated delay of aging.

Gene pathways associated with mitochondrial function, oxidative stress and telomere length are differentially expressed in the liver of rats fed lifelong on virgin olive, sunflower or fish oils

This study investigates the effect of lifelong intake of different fat sources rich in monounsaturated (virgin olive oil), n6 polyunsaturated (sunflower oil) or n3 polyunsaturated (fish oil) fatty acids in the aged liver. Male Wistar rats fed lifelong on diets differing in the fat source were killed at 6 and at 24 months of age. Liver histopathology, mitochondrial ultrastructure, biogenesis, oxidative stress, mitochondrial electron transport chain, relative telomere length and gene expression profiles were studied. Aging led to lipid accumulation in the liver. Virgin olive oil led to the lowest oxidation and ultrastructural alterations. Sunflower oil induced fibrosis, ultrastructural alterations and high oxidation. Fish oil intensified oxidation associated with age, lowered electron transport chain activity and enhanced the relative telomere length. Gene expression changes associated with age in animals fed virgin olive oil and fish oil were related mostly to mitochondrial function and oxidative stress pathways, followed by cell cycle and telomere length control. Sunflower oil avoided gene expression changes related to age. According to the results, virgin olive oil might be considered the dietary fat source that best preserves the liver during the aging process.

Caspase-2 resides in the mitochondria and mediates apoptosis directly from the mitochondrial compartment

Caspase-2 plays an important role in apoptosis induced by several stimuli, including oxidative stress. However, the subcellular localization of caspase-2, particularly its presence in the mitochondria, is unclear. It is also not known if cytosolic caspase-2 translocates to the mitochondria to trigger the intrinsic pathway of apoptosis or if caspase-2 is constitutively present in the mitochondria that then selectively mediates this apoptotic effect. Here, we demonstrate the presence of caspase-2 in purified mitochondrial fractions from in vitro-cultured cells and in liver hepatocytes using immunoblots and confocal microscopy. We show that mitochondrial caspase-2 is functionally active by performing fluorescence resonance energy transfer analyses using a mitochondrially targeted substrate flanked by donor and acceptor fluorophores. Cell-free apoptotic assays involving recombination of nuclear, cytosolic and mitochondrial fractions from the livers of wild type and Casp2^−/− mice clearly point to a direct functional role for mitochondrial caspase-2 in apoptosis. Furthermore, cytochrome c release from Casp2^−/− cells is decreased as compared with controls upon treatment with agents inducing mitochondrial dysfunction. Finally, we show that Casp2^−/− primary skin fibroblasts are protected from oxidants that target the mitochondrial electron transport chain. Taken together, our results demonstrate that caspase-2 exists in the mitochondria and that it is essential for mitochondrial oxidative stress-induced apoptosis.

Caspase-2 modulates osteoclastogenesis through down-regulating oxidative stress

The loss of caspase-2 (Casp-2) in mice results in an osteopenic phenotype associated with increased numbers of osteoclasts in vivo. In this study, we show that Casp-2 is involved in osteoclastogenesis. Protein levels of Casp-2 decrease during the differentiation of macrophages to osteoclasts. Furthermore, siRNA-mediated Casp-2 knockdown in osteoclast precursors or differentiation of bone marrow macrophage (BMM) precursors from Casp2(-/-) mice results in increased osteoclast numbers and tartrate-resistant acid phosphatase (TRAP) activity. Casp2(-/-) osteoclasts are larger in size compared to wild-type osteoclasts and exhibited increased numbers of nuclei, perhaps due to increased precursor fusion. The loss of Casp-2 did not alter earlier stages of differentiation, but had a greater consequence on later stages involving NFATc1 auto-amplification and pre-osteoclast fusion. We have previously shown that the loss of Casp-2 results in increased oxidative stress in the bone. Reactive oxygen species (ROS) is known to play a critical role in late osteoclast differentiation and we show that total ROS and specifically, mitochondrial ROS, significantly increased in Casp2(-/-) BMM precursors after RANKL administration, with a concomitant reduction in FoxO3a and its target antioxidant enzymes, catalase and superoxide 2 (SOD2). Because mitochondrial ROS has been identified as a putative regulator of the later stages of differentiation, the heightened ROS levels in Casp2(-/-) cells likely promote precursor fusion and increased osteoclast numbers. In conclusion, our results indicate a novel role of Casp-2 in the osteoclast as a modulator of total and mitochondrial ROS and osteoclast differentiation.

Caspase-2 and the oxidative stress response

Caspase-2, one of the earliest discovered caspases, has emerged as a multifunctional enzyme with roles that are not limited to cell death. It acts as a tumor suppressor, prevents genetic instability, and protects against aging by playing a crucial role in sensing alterations in cellular redox status and activating the antioxidant defense system. These apparent non-apoptotic functions, only discovered recently, emphasize the importance of this often-neglected protease.

Age-related proteostasis and metabolic alterations in Caspase-2-deficient mice

Ageing is a complex biological process for which underlying biochemical changes are still largely unknown. We performed comparative profiling of the cellular proteome and metabolome to understand the molecular basis of ageing in Caspase-2-deficient (Casp2^−/−) mice that are a model of premature ageing in the absence of overt disease. Age-related changes were determined in the liver and serum of young (6–9 week) and aged (18–24 month) wild-type and Casp2^−/− mice. We identified perturbed metabolic pathways, decreased levels of ribosomal and respiratory complex proteins and altered mitochondrial function that contribute to premature ageing in the Casp2^−/− mice. We show that the metabolic profile changes in the young Casp2^−/− mice resemble those found in aged wild-type mice. Intriguingly, aged Casp2^−/− mice were found to have reduced blood glucose and improved glucose tolerance. These results demonstrate an important role for caspase-2 in regulating proteome and metabolome remodelling during ageing.

Old, new and emerging functions of caspases

Caspases are proteases with a well-defined role in apoptosis. However, increasing evidence indicates multiple functions of caspases outside apoptosis. Caspase-1 and caspase-11 have roles in inflammation and mediating inflammatory cell death by pyroptosis. Similarly, caspase-8 has dual role in cell death, mediating both receptor-mediated apoptosis and in its absence, necroptosis. Caspase-8 also functions in maintenance and homeostasis of the adult T-cell population. Caspase-3 has important roles in tissue differentiation, regeneration and neural development in ways that are distinct and do not involve any apoptotic activity. Several other caspases have demonstrated anti-tumor roles. Notable among them are caspase-2, -8 and -14. However, increased caspase-2 and -8 expression in certain types of tumor has also been linked to promoting tumorigenesis. Increased levels of caspase-3 in tumor cells causes apoptosis and secretion of paracrine factors that promotes compensatory proliferation in surrounding normal tissues, tumor cell repopulation and presents a barrier for effective therapeutic strategies. Besides this caspase-2 has emerged as a unique caspase with potential roles in maintaining genomic stability, metabolism, autophagy and aging. The present review focuses on some of these less studied and emerging functions of mammalian caspases.