Ultrastructural features and prevalence of tubuloreticular structures in the ocular vasculature of patients with AIDS: a study of 23 cases

The Role of Membranes and Lipid-Protein Interactions in the Mg-Branch of Tetrapyrrole Biosynthesis

Chlorophyll (Chl) is essential for photosynthesis and needs to be produced throughout the whole plant life, especially under changing light intensity and stress conditions which may result in the destruction and elimination of these pigments. All steps of the Mg-branch of tetrapyrrole biosynthesis leading to Chl formation are carried out by enzymes associated with plastid membranes. Still the significance of these protein-membrane and protein-lipid interactions in Chl synthesis and chloroplast differentiation are not very well-understood. In this review, we provide an overview on Chl biosynthesis in angiosperms with emphasis on its association with membranes and lipids. Moreover, the last steps of the pathway including the reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), the biosynthesis of the isoprenoid phytyl moiety and the esterification of Chlide are also summarized. The unique biochemical and photophysical properties of the light-dependent NADPH:protochlorophyllide oxidoreductase (LPOR) enzyme catalyzing Pchlide photoreduction and located to peculiar tubuloreticular prolamellar body (PLB) membranes of light-deprived tissues of angiosperms and to envelope membranes, as well as to thylakoids (especially grana margins) are also reviewed. Data about the factors influencing tubuloreticular membrane formation within cells, the spectroscopic properties and the in vitro reconstitution of the native LPOR enzyme complexes are also critically discussed.

Coronavirus-Induced Host Cubic Membranes and Lipid-Related Antiviral Therapies: A Focus on Bioactive Plasmalogens

Coronaviruses have lipid envelopes required for their activity. The fact that coronavirus infection provokes the formation of cubic membranes (CM) (denoted also as convoluted membranes) in host cells has not been rationalized in the development of antiviral therapies yet. In this context, the role of bioactive plasmalogens (vinyl ether glycerophospholipids) is not completely understood. These lipid species display a propensity for non-lamellar phase formation, facilitating membrane fusion, and modulate the activity of membrane-bound proteins such as enzymes and receptors. At the organism level, plasmalogen deficiency is associated with cardiometabolic disorders including obesity and type 2 diabetes in humans. A straight link is perceived with the susceptibility of such patients to SARS-CoV-2 (severe acute respiratory syndrome-coronavirus-2) infection, the severity of illness, and the related difficulty in treatment. Based on correlations between the coronavirus-induced modifications of lipid metabolism in host cells, plasmalogen deficiency in the lung surfactant of COVID-19 patients, and the alterations of lipid membrane structural organization and composition including the induction of CM, we emphasize the key role of plasmalogens in the coronavirus (SARS-CoV-2, SARS-CoV, or MERS-CoV) entry and replication in host cells. Considering that plasmalogen-enriched lung surfactant formulations may improve the respiratory process in severe infected individuals, plasmalogens can be suggested as an anti-viral prophylactic, a lipid biomarker in SARS-CoV and SARS-CoV-2 infections, and a potential anti-viral therapeutic component of lung surfactant development for COVID-19 patients.

The significance of tubuloreticular inclusions as a marker of systemic stimulation by interferons in a case of focal and segmental glomerulosclerosis associated with cytomegalovirus (CMV) infection

The identification of large numbers of tubuloreticular inclusions (TRIs) in renal biopsies may be useful to raise diagnostic suspicion for certain clinical entities, particularly autoimmune diseases and viral infections. We report a case of a 65-year-old female with a 2-week history of malaise, massive proteinuria and lower extremity edema of acute onset. A renal biopsy was performed and the diagnosis of non-human immunodeficiency virus (HIV) tip-located, early focal segmental glomerulosclerosis (FSGS) was established. The electron microscopy examination was remarkable for the presence of diffuse foot process effacement and frequent TRIs in the endothelial cells of the glomerular capillary loops, endothelium of arterioles and cytoplasm of fibroblasts in the interstitium, highly suggestive of an underlying etiology. Patient clinical and laboratory workup revealed the absence of an autoimmune disease but the presence of a subclinical cytomegalovirus (CMV) infection. Therefore, we highlight that the identification of TRIs is a useful indicator of systemic interferon activity. In the present case, the unusual location of numerous TRIs was associated with a subclinical CMV infection in an immunocompetent patient.

Tubuloreticular structures in rectal biopsies of SIV-infected rhesus monkeys (Macaca mulatta)

Tubuloreticular structures (TRS) are considered to be a specific ultrastructural marker for AIDS in various organs. Experimental SIV infection in rhesus macaques is the most appropriate animal model of HIV infection. In 8 rhesus monkeys, experimentally infected with SIVmac251/MPBC, rectum biopsies were taken prior to and post infection (day 3; 1, 2, 4, 12 weeks p.i.) and were investigated by transmissionelectron microscopy to determine incidence and extent of tubuloreticular structures as well as affected cells. From the first week p.i. on TRS were found in all experimental animals as tubuli with a diameter of 20-30 nm. The tubuli were arranged in regular paracristalline formations and formed intracytoplasmatic heterogenous, polymorph accumulations, which were localized close to the endoplasmatic reticulum. In the rectal lamina propria macrophages, endothelial cells, plasma cells, lymphocytes, fibroblasts, and neutrophilic granulocytes were the affected cell types. In 5 control biopsies TRS were detected, too, but, in contrast to SIV-infected animals, they appeared only singular and very small. The results indicate that TRS are a characteristic morphologic criteria of intestinal SIV infection. They appear in very early stages of the infection. In the rectum, they can be detected as bigger, conspicuous, and abundant formations in several cells and have a restricted diagnostic and prognostic validity.