Presence of calpain-5 in mitochondria

Treatment and Visual Outcomes in Pediatric Patients with Autosomal Dominant Neovascular Inflammatory Vitreoretinopathy: A Cohort Study

BACKGROUND

Autosomal dominant neovascular inflammatory vitreoretinopathy (NIV), formerly called "ADNIV," is a rare autoinflammatory condition mainly of adulthood caused by mutations in calcium-activated calpain-5 protease (CAPN5). Our aim is to report the treatment and visual outcomes of children newly diagnosed with NIV after systemic treatment.

METHODS

We reviewed charts of patients ≤18 years old with CAPN5 gene mutation, ocular findings consistent with NIV, and treated with systemic immunosuppression for a minimum of 6 months. Treatment response was based on ophthalmic examination, ultra-widefield fluorescein-angiography (UWFFA), and optical coherence tomography (OCT).

RESULTS

Eight children (16 eyes) were diagnosed with NIV at a median age of 14 (Range [R] 9-16) years, with a median follow-up of 18 months (R6-20). At diagnosis, one patient had impaired visual acuity (VA > 0.4), eight had vascular leakage, two had neovascularization, and three had macular edema. All responded to oral or local glucocorticoids but was not sustained. Systemic immunosuppression was started in seven patients with methotrexate and infliximab after a median time from diagnosis of 1.5 months (R0.5-2) and 3.2 months (R2.5-3.1), respectively. Infliximab was discontinued in all after a median time of 7 months (R3.5-10) for ineffectiveness, and 5/7 switched to tocilizumab and 1 to adalimumab. Five failed to respond (4 tocilizumab, 1 adalimumab) and one had a minimal response to tocilizumab.

CONCLUSIONS

We report on the systemic treatment response of seven children with ADNIV treated with methotrexate, infliximab, and tocilizumab. None were able to control disease. Further studies are needed to understand long-term outcomes and the utility of systemic immunosuppression.

Proteolysis of mitochondrial calpain-13 in cerebral ischemia-reperfusion injury

Calpains are calcium-dependent cysteine proteases activated by intracellular Ca2+. Although calpains mainly exist in the cytosol, calpain-13 is present in the mitochondria in mouse brains; however, the enzymatic properties and physiological functions of calpain-13 remain unknown. Hence, in this study, we predicted and evaluated the enzymatic properties of calpain-13. Based on our bioinformatic approaches, calpain-13 possessed a catalytic triad and EF-hand domain, similar to calpain-1, a well-studied calpain. Therefore, we hypothesized that calpain-13 had calpain-1-like enzymatic properties; however, calpain-13 was not proteolyzed in C57BL/6J mouse brains. Subsequently, cerebral ischemia/reperfusion (I/R) injury caused proteolysis of mitochondrial calpain-13. Thus, our study showed that mitochondrial calpain-13 was proteolyzed in the mitochondria of the I/R injured mouse brain. This finding could be valuable in further research elucidating the involvement of calpain-13 in cell survival or death in brain diseases, such as cerebral infarction.

Role of calpain-5 in cerebral ischemia and reperfusion injury

BACKGROUND

Ischemia and reperfusion (I/R) injury exacerbate the prognosis of ischemic diseases. The cause of this exacerbation is partly a mitochondrial cell death pathway. Mitochondrial calpain-5 is proteolyzed/autolyzed under endoplasmic reticulum stress, resulting in inflammatory caspase-4 activation. However, the role of calpain-5 in I/R injury remains unclear. We hypothesized that calpain-5 is involved in ischemic brain disease.

METHODS

Mitochondria from C57BL/6J mice were extracted via centrifugation with/without proteinase K treatment. The expression and proteolysis/autolysis of calpain-5 were determined using western blotting. The mouse and human brains with I/R injury were analyzed using hematoxylin and eosin staining and immunohistochemistry. HT22 cells were treated with tunicamycin and CAPN5 siRNA.

RESULTS

Calpain-5 was expressed in the mitochondria of mouse tissues. Mitochondrial calpain-5 in mouse brains was responsive to calcium earlier than cytosolic calpain-5 in vitro calcium assays and in vivo bilateral common carotid artery occlusion model mice. Immunohistochemistry revealed that neurons were positive for calpain-5 in the normal brains of mice and humans. The expression of calpain-5 was increased in reactive astrocytes at human infarction sites. The knockdown of calpain-5 suppressed of cleaved caspase-11.

CONCLUSIONS

The neurons of human and mouse brains express calpain-5, which is proteolyzed/autolyzed in the mitochondria in the early stage of I/R injury and upregulated in reactive astrocytes in the end-stage.

GENERAL SIGNIFICANCE

Our results provide a comprehensive understanding of the mechanisms underlying I/R injury. Targeting the expression or activity of mitochondrial calpain-5 may suppress the inflammation during I/R injuries such as cerebrovascular diseases.

Calpain-1 C2L domain peptide protects mouse hippocampus-derived neuronal HT22 cells against glutamate-induced oxytosis

Calpains are Ca²⁺-dependent cysteine proteases; their aberrant activation is associated with several neurodegenerative diseases. The μ-calpain catalytic subunit, calpain-1, is located in the cytoplasm as well as in the mitochondria. Mitochondrial calpain-1 cleaves apoptosis-inducing factor (AIF), leading to apoptotic cell death. We have previously reported that short peptides of calpain-1 C2-like domain conjugated with cell penetrating peptide HIV-Tat (Tat-μCL) selectively inhibit mitochondrial calpain-1 and effectively prevent neurodegenerative diseases of the eye. In this study, we determined whether mitochondrial calpain-1 mediates oxytosis (oxidative glutamate toxicity) in hippocampal HT22 cells using Tat-μCL and newly generated polyhistidine-conjugated μCL peptide and compared their efficacies in preventing oxytosis. TUNEL assay and single strand DNA staining revealed that both μCL peptides inhibited glutamate-induced oxytosis. Additionally, both the peptides suppressed the mitochondrial AIF translocation into the nucleus. All polyhistidine-μCL peptides (containing 4–16 histidine residues) showed higher cell permeability than Tat-μCL. Notably, tetrahistidine (H4)-μCL exerted the highest cytoprotective activity. Thus, H4-μCL may be a potential peptide drug for calpain-1-mediated neurodegenerative diseases such as Alzheimer's disease.

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Mitochondrial calpain-1 mediates glutamate-induced oxytosis in HT22 cells.

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CPP-μCL inhibits AIF translocation and DNA fragmentation in oxytosis.

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Polyhistidine conjugation enhances intracellular μCL peptide uptake efficiency.

Mitochondrial nucleoid in cardiac homeostasis: bidirectional signaling of mitochondria and nucleus in cardiac diseases

Metabolic function and energy production in eukaryotic cells are regulated by mitochondria, which have been recognized as the intracellular 'powerhouses' of eukaryotic cells for their regulation of cellular homeostasis. Mitochondrial function is important not only in normal developmental and physiological processes, but also in a variety of human pathologies, including cardiac diseases. An emerging topic in the field of cardiovascular medicine is the implication of mitochondrial nucleoid for metabolic reprogramming. This review describes the linear/3D architecture of the mitochondrial nucleoid (e.g., highly organized protein-DNA structure of nucleoid) and how it is regulated by a variety of factors, such as noncoding RNA and its associated R-loop, for metabolic reprogramming in cardiac diseases. In addition, we highlight many of the presently unsolved questions regarding cardiac metabolism in terms of bidirectional signaling of mitochondrial nucleoid and 3D chromatin structure in the nucleus. In particular, we explore novel techniques to dissect the 3D structure of mitochondrial nucleoid and propose new insights into the mitochondrial retrograde signaling, and how it regulates the nuclear (3D) chromatin structures in mitochondrial diseases.

Integrated miRNA-mRNA analysis provides potential biomarkers for selective breeding in bay scallop (Argopecten irradians)

Growth traits were compared between selected Argopecten irradians (BA) and non-selected A. irradians (NA; as a control). The results indicated that 1) the BA line exhibited greater average body weight and adductor muscle wet weight increase compared with the NA line at the same age of 10 months. 2) Comparative and integrated microRNA (miRNA) and mRNA transcriptome analyses identified 3373 differentially expressed genes (DEGs), 33 differentially expressed miRNAs (DEMs), and 39 "DEM-DEG" pairs in the BA line compared with the control. DEGs, DEMs, and "DEM-DEG" pairs involved in insulin signaling, immune related pathways, and actin cytoskeleton regulation were identified as candidates correlated with growth improvement in the BA line. A total of 259 positively selected genes were also identified. Collectively, our observations in this study will enrich the molecular information for A. irradians and provide potential biomarkers for future selective breeding and new seed creation in scallops.

Characterization of mitochondrial calpain-5

Calpain, a Ca²⁺-dependent cysteine protease, plays a significant role in gene expression, signal transduction, and apoptosis. Mutations in human calpain-5 cause autosomal dominant neovascular inflammatory vitreoretinopathy and the inhibition of calpain-5 activity may constitute an effective therapeutic strategy for this condition. Although calpain-5 is ubiquitously expressed in mammalian tissues and was recently found to be present in the mitochondria as well as in the cytosol, its physiological function and enzymological properties require further elucidation. The objective of the current study was to determine the characteristics of mitochondrial calpain-5 in porcine retinas, human HeLa cells, and C57BL/6J mice using subcellular fractionation. We found that mitochondrial calpain-5 was proteolyzed/autolyzed at low Ca²⁺ concentrations in mitochondria isolated from porcine retinas and by thapsigargin-induced endoplasmic reticulum (ER) stress in HeLa cells. Further, mitochondrial calpain-5, as opposed to cytosolic calpain-5, was activated during the early stages of ER stress in C57BL/6J mice. These results showed that mitochondrial calpain-5 was activated at low Ca²⁺ concentrations in vitro and in response to ER stress in vivo. The present study provides new insights into a novel calpain system in the mitochondria that includes stress responses during the early phases of ER stress. Further, activation of mitochondrial calpain-5 by treatment using low-molecular-weight compounds may have therapeutic potential for diseases related to ER stress, including neurodegenerative diseases, metabolic syndromes, diabetes, and cancer.

Data on mitochondrial ultrastructure of photoreceptors in pig, rabbit, and mouse retinas

Photoreceptors are one of the most energy-consuming cell types within the human body. To meet their high energy demand, photoreceptors possess a mitochondrial cluster in the inner segment of the cell. Interestingly, in several species, the inner segment of cone photoreceptors contains extremely large mitochondria that exceed 2 µm in diameter, called mega-mitochondria. We previously reported that pig retinas also contain mega-mitochondria, however, there are few reports whether mega-mitochondria are present in mammalian photoreceptors. In the present experiment, we analyzed pig, rabbit, and mouse photoreceptors under a scanning electron microscope (SEM), and compared the mitochondrial morphology. Our data showed that all three species present numerous mitochondrial clusters in the ellipsoid zone of photoreceptors, adjacent to the outer segment. In the pig retina, the inner segments of cone and rod photoreceptors were localized in different layers; consequently, we were able to distinguish them easily. Mega-mitochondria were identified only in the inner segment of cone photoreceptors. Also, mitochondria of cone photoreceptors, including mega-mitochondria, were dense cristae and high electron-densities compared to those of rod photoreceptors. In the rabbit retina, cone photoreceptors were existed within the layer of rod photoreceptor outer segment. The rod photoreceptors had a characteristic long outer segment. Cone photoreceptors had a short outer segment, and also had a thick inner segment compared to rod photoreceptors. Most of the mitochondria present in the rod photoreceptor inner segment were long and narrow, whereas mitochondria of cone photoreceptors were fragmented and short. Mega-mitochondria was not detected in rabbit retina. In the mouse retina, most of the photoreceptor cells were rod photoreceptors. Since the shape of the inner segments were very similar, we distinguished cone and rod photoreceptors based on the shape of the outer segments. Some mitochondria of both rod and cone photoreceptors were long and narrow, and there was no significant difference in mitochondrial morphology. Our data showed that mitochondrial morphology in the inner segment of photoreceptors vary among mammalian species. Although mega-mitochondria were present in pig photoreceptors, we could not observe their presence in rabbit nor mouse retinas. To our knowledge, this is a first experiment that perform the wide field observation of rabbit and mouse retina using electron microscopy, and that compare the mitochondrial morphology of photoreceptor cells in pig, rabbit and mouse.