Electrical stimulation of cardiomyocytes activates mitochondrial matrix metalloproteinase causing electrical remodeling

Mechanism of Blood-Heart-Barrier Leakage: Implications for COVID-19 Induced Cardiovascular Injury

Although blood–heart-barrier (BHB) leakage is the hallmark of congestive (cardio-pulmonary) heart failure (CHF), the primary cause of death in elderly, and during viral myocarditis resulting from the novel coronavirus variants such as the severe acute respiratory syndrome novel corona virus 2 (SARS-CoV-2) known as COVID-19, the mechanism is unclear. The goal of this project is to determine the mechanism of the BHB in CHF. Endocardial endothelium (EE) is the BHB against leakage of blood from endocardium to the interstitium; however, this BHB is broken during CHF. Previous studies from our laboratory, and others have shown a robust activation of matrix metalloproteinase-9 (MMP-9) during CHF. MMP-9 degrades the connexins leading to EE dysfunction. We demonstrated juxtacrine coupling of EE with myocyte and mitochondria (Mito) but how it works still remains at large. To test whether activation of MMP-9 causes EE barrier dysfunction, we hypothesized that if that were the case then treatment with hydroxychloroquine (HCQ) could, in fact, inhibit MMP-9, and thus preserve the EE barrier/juxtacrine signaling, and synchronous endothelial-myocyte coupling. To determine this, CHF was created by aorta-vena cava fistula (AVF) employing the mouse as a model system. The sham, and AVF mice were treated with HCQ. Cardiac hypertrophy, tissue remodeling-induced mitochondrial-myocyte, and endothelial-myocyte contractions were measured. Microvascular leakage was measured using FITC-albumin conjugate. The cardiac function was measured by echocardiography (Echo). Results suggest that MMP-9 activation, endocardial endothelial leakage, endothelial-myocyte (E-M) uncoupling, dyssynchronous mitochondrial fusion-fission (Mfn2/Drp1 ratio), and mito-myocyte uncoupling in the AVF heart failure were found to be rampant; however, treatment with HCQ successfully mitigated some of the deleterious cardiac alterations during CHF. The findings have direct relevance to the gamut of cardiac manifestations, and the resultant phenotypes arising from the ongoing complications of COVID-19 in human subjects.

Matrix metalloproteinases participation in the metastatic process and their diagnostic and therapeutic applications in cancer

Matrix metalloproteinases (MMPs) participate from the initial phases of cancer onset to the settlement of a metastatic niche in a second organ. Their role in cancer progression is related to their involvement in the extracellular matrix (ECM) degradation and in the regulation and processing of adhesion and cytoskeletal proteins, growth factors, chemokines and cytokines. MMPs participation in cancer progression makes them an attractive target for cancer therapy. MMPs have also been used for theranostic purposes in the detection of primary tumor and metastatic tissue in which a particular MMP is overexpressed, to follow up on therapy responses, and in the activation of cancer cytotoxic pro-drugs as part of nano-delivery-systems that increase drug concentration in a specific tumor target. Herein, we review MMPs molecular characteristics, their synthesis regulation and enzymatic activity, their participation in the metastatic process, and how their functions have been used to improve cancer treatment.

Birefringence of Collagen Fibres in Rat Calcaneal Tendons Treated with Acupuncture during Three Phases of Healing

Background

Birefringence is an optical anisotropy that is investigated by polarisation microscopy, and has been valuable for the study of the oriented organisation of collagen fibres in tendons. However, the application of this technology to evaluate the effect of different acupuncture points during tendon healing has not yet been described.

Objectives

To evaluate the concentration of non-collagenous proteins (NCP) and birefringence in rat calcaneal tendons following injury during the three different phases of healing: inflammatory (7th day), proliferative (14th day), and remodelling (21st day).

Methods

Tendons of 120 Wistar rats were tenotomised and left untreated (teno group, n=24), treated with manual acupuncture at ST36 (ST36 group, n=24), BL57 (BL57 group, n=24) or ST36+BL57 (SB group, n=24), or treated with electroacupuncture at ST36+BL57 (EA group, n=24). Tendon samples were collected at 7, 14 and 21 days after injury (n=8 per group). NCP concentrations were measured using the Bradford method (n=4 each) and birefringence was examined using polarisation microscopy and image analysis (n=4 each). Comparison was also made with healthy (non-tenotomised) tendons in a subgroup of rats (n=4 each).

Results

Manual acupuncture at ST36 and BL57 increased molecular organisation of collagen fibres on day 14 and 21 after injury. Isolated use of BL57 and ST36 also increased collagen fibre organisation when examined on day 14 and 21, respectively. No significant increase in NCP concentration was observed in any of the treated tenotomised groups.

Conclusions

Acupuncture, through putative anti-inflammatory and mechanotransductor effects, may have a role in strengthening tendons and increasing resistance to re-rupture.

Heart-on-a-chip based on stem cell biology

Heart diseases are one of the main causes of death around the world. The great challenge for scientists is to develop new therapeutic methods for these types of ailments. Stem cells (SCs) therapy could be one of a promising technique used for renewal of cardiac cells and treatment of heart diseases. Conventional in vitro techniques utilized for investigation of heart regeneration do not mimic natural cardiac physiology. Lab-on-a-chip systems may be the solution which could allow the creation of a heart muscle model, enabling the growth of cardiac cells in conditions similar to in vivo conditions. Microsystems can be also used for differentiation of stem cells into heart cells, successfully. It will help better understand of proliferation and regeneration ability of these cells. In this review, we present Heart-on-a-chip systems based on cardiac cell culture and stem cell biology. This review begins with the description of the physiological environment and the functions of the heart. Next, we shortly described conventional techniques of stem cells differentiation into the cardiac cells. This review is mostly focused on describing Lab-on-a-chip systems for cardiac tissue engineering. Therefore, in the next part of this article, the microsystems for both cardiac cell culture and SCs differentiation into cardiac cells are described. The section about SCs differentiation into the heart cells is divided in sections describing biochemical, physical and mechanical stimulations. Finally, we outline present challenges and future research concerning Heart-on-a-chip based on stem cell biology.

Electrical and Mechanical Strategies to Enable Cardiac Repair and Regeneration

Inadequate replacement of lost ventricular myocardium from myocardial infarction leads to heart failure. Investigating the regenerative capacity of mammalian hearts represents an emerging direction for tissue engineering and cell-based therapy. Recent advances in stem cells hold promise to restore cardiac functions. However, embryonic or induced pluripotent stem cell-derived cardiomyocytes lack functional phenotypes of the native myocardium, and transplanted tissues are not fully integrated for synchronized electrical and mechanical coupling with the host. In this context, this review highlights the mechanical and electrical strategies to promote cardiomyocyte maturation and integration, and to assess the functional phenotypes of regenerating myocardium. Simultaneous microelectrocardiogram and high-frequency ultrasound techniques will also be introduced to assess electrical and mechanical coupling for small animal models of heart regeneration.

Acupuncture Increases the Diameter and Reorganisation of Collagen Fibrils during Rat Tendon Healing

Background

Our previous study showed that electroacupuncture (EA) increases the concentration and reorganisation of collagen in a rat model of tendon healing. However, the ultrastructure of collagen fibrils after acupuncture is unknown.

Objectives

To assess the effect of acupuncture protocols on the ultrastructure of collagen fibrils during tendon healing.

Methods

Sixty-four rats were divided into the following groups: non-tenotomised (normal group), tenotomised (teno group), tenotomised and subjected to manual acupuncture at ST36 (ST36 group), BL57 (BL57 group) and ST36+BL57 (SB group) and EA at ST36+BL57 (EA group). The mass-average diameter (MAD) and the reorganisation of collagen fibril diameters were determined during the three phases of tendon healing (at 7, 14 and 21 days).

Results

The MAD increased during the three phases of healing in the SB group. In the EA group, MAD increased initially but was reduced at day 21. The reorganisation of collagen fibrils was improved in the EA and SB groups at days 14 and 21, respectively. EA at day 21 appeared to reduce the reorganisation.

Conclusions

These results indicate that the use of EA up to day 14 and manual acupuncture at ST36+BL57 up to day 21 improve the ultrastructure of collagen fibrils, indicating strengthening of the tendon structure. These data suggest a potential role for acupuncture in rehabilitation protocols.

Dysregulation of Mfn2 and Drp-1 proteins in heart failure

Therapeutic approaches for cardiac regenerative mechanisms have been explored over the past decade to target various cardiovascular diseases (CVD). Structural and functional aberrations of mitochondria have been observed in CVD. The significance of mitochondrial maturation and function in cardiomyocytes is distinguished by their attribution to embryonic stem cell differentiation into adult cardiomyocytes. An abnormal fission process has been implicated in heart failure, and treatment with mitochondrial division inhibitor 1 (Mdivi-1), a specific inhibitor of dynamin related protein-1 (Drp-1), has been shown to improve cardiac function. We recently observed that the ratio of mitofusin 2 (Mfn2; a fusion protein) and Drp-1 (a fission protein) was decreased during heart failure, suggesting increased mitophagy. Treatment with Mdivi-1 improved cardiac function by normalizing this ratio. Aberrant mitophagy and enhanced oxidative stress in the mitochondria contribute to abnormal activation of MMP-9, leading to degradation of the important gap junction protein connexin-43 (Cx-43) in the ventricular myocardium. Reduced Cx-43 levels were associated with increased fibrosis and ventricular dysfunction in heart failure. Treatment with Mdivi-1 restored MMP-9 and Cx-43 expression towards normal. In this review, we discuss mitochondrial dynamics, its relation to MMP-9 and Cx-43, and the therapeutic role of fission inhibition in heart failure.

MMP-2 is localized to the mitochondria-associated membrane of the heart

Matrix metalloproteinase-2 (MMP-2) has been extensively studied in the context of extracellular matrix remodeling but is also localized within cells and can be activated by prooxidants to proteolyze specific intercellular targets. Although there are reports of MMP-2 in mitochondria, a critical source of cellular oxidative stress, these studies did not take into account the presence within their preparations of the mitochondria-associated membrane (MAM), a subdomain of the endoplasmic reticulum (ER). We hypothesized that MMP-2 is situated in the MAM and therefore investigated its subcellular distribution between mitochondria and the MAM. Immunogold electron microscopy revealed MMP-2 localized in mitochondria of heart sections from mice. In contrast, immunofluorescence analysis of an MMP-2:HaloTag fusion protein expressed in HL-1 cardiomyocytes showed an ER-like distribution, with greater colocalization with an ER marker (protein disulfide isomerase) relative to the mitochondrial marker, MitoTracker red. Although MMP-2 protein and enzymatic activity were present in crude mitochondrial fractions, once these were separated into purified mitochondria and MAM, MMP-2 was principally associated with the latter. Thus, although mitochondria may contain minimal levels of MMP-2, the majority of MMP-2 previously identified as "mitochondrial" is in fact associated with the MAM. We also found that calreticulin, an ER- and MAM-resident Ca(2+) handling protein and chaperone, could be proteolyzed by MMP-2 in vitro. MAM-localized MMP-2 could therefore potentially impact mitochondrial function by affecting ER-mitochondrial Ca(2+) signaling via its proteolysis of calreticulin.

Homocysteine induces COX-2 expression in macrophages through ROS generated by NMDA receptor-calcium signaling pathways

Homocysteine (Hcy) at elevated levels is a putative risk factor for many cardiovascular disorders including atherosclerosis. In the present study, we investigated the effect of Hcy on the expression of cyclooxygenase (COX)-2 in murine macrophages and the mechanisms involved. Hcy increased the expression of COX-2 mRNA and protein in dose- and time-dependent manners, but did not affect COX-1 expression. Hcy-induced COX-2 expression was attenuated not only by the calcium chelators, EGTA and BAPTA-AM, but also by an antioxidant, N-acetylcysteine. Calcium chelators also attenuated Hcy-induced reactive oxygen species (ROS) production in macrophages, indicating that Hcy-induced COX-2 expression might be mediated through ROS generated by calcium-dependent signaling pathways. In another series of experiments, Hcy increased the intracellular concentration of calcium in a dose-dependent manner, which was attenuated by MK-801, an N-methyl-D-aspartate (NMDA) receptor inhibitor, but not by bicuculline, a gamma-aminobutyric acid receptor inhibitor. Molecular inhibition of NMDA receptor using small interfering RNA also attenuated Hcy-induced increases in intracellular calcium. Furthermore, both ROS production and Hcy-induced COX-2 expression were also inhibited by MK-801 as well as by molecular inhibition of NMDA receptor. Taken together, these findings suggest that Hcy enhances COX-2 expression in murine macrophages by ROS generated via NMDA receptor-mediated calcium signaling pathways.

Abrogation of MMP-9 gene protects against the development of retinopathy in diabetic mice by preventing mitochondrial damage

OBJECTIVE

In the development of diabetic retinopathy, mitochondrial dysfunction is considered to play an important role in the apoptosis of retinal capillary cells. Diabetes activates matrix metalloproteinase-9 (MMP-9) in the retina and its capillary cells, and activated MMP-9 becomes proapoptotic. The objective of this study is to elucidate the plausible mechanism by which active MMP-9 contributes to the mitochondrial dysfunction in the retina.

RESEARCH DESIGN AND METHODS

Using MMP-9 gene knockout (MMP-KO) mice, we investigated the effect of MMP-9 regulation on diabetes-induced increased retinal capillary cell apoptosis, development of retinopathy, mitochondrial dysfunction and ultrastructure, and mitochondrial DNA (mtDNA) damage. To understand how diabetes increases mitochondrial accumulation of MMP-9, interactions between MMP-9 and chaperone proteins (heat shock protein [Hsp] 70 and Hsp60) were evaluated. The results were confirmed in the retinal mitochondria from human donors with diabetic retinopathy, and in isolated retinal endothelial cells transfected with MMP-9 small interfering RNA (siRNA).

RESULTS

Retinal microvasculature of MMP-KO mice, diabetic for ∼7 months, did not show increased apoptosis and pathology characteristic of retinopathy. In the same MMP-KO diabetic mice, activation of MMP-9 and dysfunction of the mitochondria were prevented, and electron microscopy of the retinal microvasculature region revealed normal mitochondrial matrix and packed lamellar cristae. Damage to mtDNA was protected, and the binding of MMP-9 with Hsp70 or Hsp60 was also normal. As in the retina from wild-type diabetic mice, activation of mitochondrial MMP-9 and alterations in the binding of MMP-9 with chaperone proteins were also observed in the retina from donors with diabetic retinopathy. In endothelial cells transfected with MMP-9 siRNA, high glucose-induced damage to the mitochondria and the chaperone machinery was ameliorated.

CONCLUSIONS

Regulation of activated MMP-9 prevents retinal capillary cells from undergoing apoptosis by protecting mitochondrial ultrastructure and function and preventing mtDNA damage. Thus, MMP-9 inhibitors could have potential therapeutic value in preventing the development of diabetic retinopathy by preventing the continuation of the vicious cycle of mitochondrial damage.