Sustained pigmentation causes DNA damage and invokes translesion polymerase Polκ for repair in melanocytes.

Melanin protects skin cells from ultraviolet radiation-induced DNA damage. However, intermediates of eumelanin are highly reactive quinones that are potentially genotoxic. In this study, we systematically investigate the effect of sustained elevation of melanogenesis and map the consequent cellular repair response of melanocytes. Pigmentation increases γH2AX foci, DNA abasic sites, causes replication stress and invokes translesion polymerase Polκ in primary human melanocytes, as well as mouse melanoma cells. Confirming the causal link, CRISPR-based genetic ablation of tyrosinase results in depigmented cells with low Polκ levels. During pigmentation, Polκ activates replication stress response and keeps a check on uncontrolled proliferation of cells harboring melanin-damaged DNA. The mutational landscape observed in human melanoma could in part explain the error-prone bypass of DNA lesions by Polκ, whose absence would lead to genome instability. Thereby, translesion polymerase Polκ is a critical response of pigmenting melanocytes to combat melanin-induced DNA alterations. Our study illuminates the dark side of melanin and identifies (eu)melanogenesis as a key missing link between tanning response and mutagenesis, mediated via the necessary evil translesion polymerase, Polκ.

Mitochondrial calcium signaling mediated transcriptional regulation of keratin filaments is a critical determinant of melanogenesis.

Mitochondria are versatile organelles that regulate several physiological functions. Many mitochondria-controlled processes are driven by mitochondrial Ca2+ signaling. However, role of mitochondrial Ca2+ signaling in melanosome biology remains unknown. Here, we show that pigmentation requires mitochondrial Ca2+ uptake. In vitro gain and loss of function studies demonstrated that Mitochondrial Ca2+ Uniporter (MCU) is crucial for melanogenesis while the MCU rheostats, MCUb and MICU1 negatively control melanogenesis. Zebrafish and mouse models showed that MCU plays a vital role in pigmentation in vivo. Mechanistically, MCU controls activation of transcription factor NFAT2 to induce expression of three keratins (keratin 5, 7 and 8), which we report as positive regulators of melanogenesis. Interestingly, keratin 5 in turn modulates mitochondrial Ca2+ uptake thereby this signaling module acts as a negative feedback loop that fine-tunes both mitochondrial Ca2+ signaling and melanogenesis. Mitoxantrone, an FDA approved drug that inhibits MCU, decreases physiological melanogenesis. Collectively, our data demonstrates a critical role for mitochondrial Ca2+ signaling in vertebrate pigmentation and reveal the therapeutic potential of targeting MCU for clinical management of pigmentary disorders. Given the centrality of mitochondrial Ca2+ signaling and keratin filaments in cellular physiology, this feedback loop may be functional in a variety of other pathophysiological conditions.

Potential of targeting host cell calcium dynamics to curtail SARS-CoV-2 infection and COVID-19 pathogenesis.

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) infection and associated coronavirus disease 2019 (COVID-19) has severely impacted human well-being. Although vaccination programs have helped in reducing the severity of the disease, drug regimens for clinical management of COVID-19 are not well recognized yet. It is therefore important to identify and characterize the molecular pathways that could be therapeutically targeted to halt SARS-CoV-2 infection and COVID-19 pathogenesis. SARS-CoV-2 hijacks host cell molecular machinery for its entry, replication and egress. Interestingly, SARS-CoV-2 interacts with host cell Calcium (Ca2+) handling proteins and perturbs Ca2+ homeostasis. We here systematically review the literature that demonstrates a critical role of host cell Ca2+ dynamics in regulating SARS-CoV-2 infection and COVID-19 pathogenesis. Further, we discuss recent studies, which have reported that SARS-CoV-2 acts on several organelle-specific Ca2+ transport mechanisms. Moreover, we deliberate upon the possibility of curtailing SARS-CoV-2 infection by targeting host cell Ca2+ handling machinery. Importantly, we delve into the clinical trials that are examining the efficacy of FDA-approved small molecules acting on Ca2+ handling machinery for the management of COVID-19. Although an important role of host cell Ca2+ signaling in driving SARS-CoV-2 infection has emerged, the underlying molecular mechanisms remain poorly understood. In future, it would be important to investigate in detail the signaling cascades that connect perturbed Ca2+ dynamics to SARS-CoV-2 infection.

Temporal analysis of melanogenesis identifies fatty acid metabolism as key skin pigment regulator.

Therapeutic methods to modulate skin pigmentation has important implications for skin cancer prevention and for treating cutaneous hyperpigmentary conditions. Towards defining new potential targets, we followed temporal dynamics of melanogenesis using a cell-autonomous pigmentation model. Our study elucidates 3 dominant phases of synchronized metabolic and transcriptional reprogramming. The melanogenic trigger is associated with high MITF levels along with rapid uptake of glucose. The transition to pigmented state is accompanied by increased glucose channelisation to anabolic pathways that support melanosome biogenesis. SREBF1-mediated up-regulation of fatty acid synthesis results in a transient accumulation of lipid droplets and enhancement of fatty acids oxidation through mitochondrial respiration. While this heightened bioenergetic activity is important to sustain melanogenesis, it impairs mitochondria lately, shifting the metabolism towards glycolysis. This recovery phase is accompanied by activation of the NRF2 detoxication pathway. Finally, we show that inhibitors of lipid metabolism can resolve hyperpigmentary conditions in a guinea pig UV-tanning model. Our study reveals rewiring of the metabolic circuit during melanogenesis, and fatty acid metabolism as a potential therapeutic target in a variety of cutaneous diseases manifesting hyperpigmentary phenotype.

Cobalt-related cardiomyopathy: A real concern! A review of published evidence.

BACKGROUND: Cobalt (Co) toxicity-related cardiomyopathy (CMP) in hip arthroplasty has recently been reported in the literature. The purpose of this review was to identify and assess available published evidence of CMP in hip arthroplasty patients and to derive recommendations for management. METHODS: We evaluated 23 cases reported till October 2018 and stratified into three categories, based on pre-existing risk factors for CMP, histological confirmation and evidence of systemic signs of Co toxicity. RESULTS: Co toxicity was considered to be the definite cause of CMP in 8 cases and probably contributory in 13 cases. Two cases were considered to have developed CMP secondary to pre-existing risk factors. Majority of the patients had good recovery of cardiac function after hip revision and cardiac management, but five cases deteriorated and died. CONCLUSION: Although Co-related CMP has been reported in a small number of cases of hip arthroplasty, a delay or missed diagnosis may lead to significant morbidity and mortality. Timely diagnosis, removal of causative implant and avoidance of metal articulations in revision for fractured ceramic implants may help in effective management.

pH-controlled histone acetylation amplifies melanocyte differentiation downstream of MITF.

Tanning response and melanocyte differentiation are mediated by the central transcription factor MITF. This involves the rapid and selective induction of melanocyte maturation genes, while concomitantly the expression of other effector genes is maintained. In this study, using cell-based and zebrafish model systems, we report on a pH-mediated feed-forward mechanism of epigenetic regulation that enables selective amplification of the melanocyte maturation program. We demonstrate that MITF activation directly elevates the expression of the enzyme carbonic anhydrase 14 (CA14). Nuclear localization of CA14 leads to an increase of the intracellular pH, resulting in the activation of the histone acetyl transferase p300/CBP. In turn, enhanced H3K27 histone acetylation at selected differentiation genes facilitates their amplified expression via MITF. CRISPR-mediated targeted missense mutation of CA14 in zebrafish results in the formation of immature acidic melanocytes with decreased pigmentation, establishing a central role for this mechanism during melanocyte differentiation in vivo. Thus, we describe an epigenetic control system via pH modulation that reinforces cell fate determination by altering chromatin dynamics.

Cobalt cardiomyopathy in hip arthroplasty.

BACKGROUND: Cobalt toxicity-related cardiomyopathy in hip arthroplasty has recently been reported in the literature. The purpose of this review is to identify and assess available published evidence of cardiomyopathy in hip arthroplasty patients and to derive recommendations for management. METHODS: We evaluated 23 cases reported until October 2018 and stratified them into 3 categories, based upon pre-existing risk factors for cardiomyopathy, histological confirmation, and evidence of systemic signs of cobalt toxicity. RESULTS: Cobalt toxicity was considered to be the definite cause of cardiomyopathy in 8 cases, and probably contributory in 13 cases. Two cases were considered to have developed cardiomyopathy secondary to pre-existing risk factors. Majority of the patients had a good recovery of cardiac function after hip revision and cardiac management, but 5 cases deteriorated and died. CONCLUSIONS: Although cobalt-related cardiomyopathy has been reported in a small number of cases of hip arthroplasty, a delay or missed diagnosis may lead to significant morbidity and mortality. Timely diagnosis, removal of causative implant, and avoidance of metal articulations in revision for fractured ceramic implants may help in an effective management.