ACE2 Receptor and TMPRSS2 Protein Expression Patterns in the Human Brainstem Reveal Anatomical Regions Potentially Vulnerable to SARS-CoV-2 Infection.

Angiotensin-converting enzyme 2 receptor (ACE2R) is a transmembrane protein expressed in various tissues throughout the body that plays a key role in the regulation of blood pressure. Recently, ACE2R has gained significant attention due to its involvement in the pathogenesis of COVID-19, the disease caused by the Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS-CoV-2). While ACE2 receptors serve as entry points for the novel coronavirus, Transmembrane Serine Protease 2 (TMPRSS2), an enzyme located on the cell membrane, is required for SARS-CoV-2 S protein priming. Even though numerous studies have assessed the effects of COVID-19 on the brain, very little information is available concerning the distribution of ACE2R and TMPRSS2 in the human brain, with particular regard to their topographical expression in the brainstem. In this study, we investigated the expression of ACE2R and TMPRSS2 in the brainstem of 18 adult subjects who died due to pneumonia/respiratory insufficiency. Our findings indicate that ACE2R and TMPRSS2 are expressed in neuronal and glial cells of the brainstem, particularly at the level of the vagal nuclei of the medulla and the midbrain tegmentum, thus confirming the expression and anatomical localization of these proteins within specific human brainstem nuclei. Furthermore, our findings help to define anatomically susceptible regions to SARS-CoV-2 infection in the brainstem, advancing knowledge on the neuropathological underpinnings of neurological manifestations in COVID-19.

Detection of SARS-CoV-2 viral proteins and genomic sequences in human brainstem nuclei.

Neurological manifestations are common in COVID-19, the disease caused by SARS-CoV-2. Despite reports of SARS-CoV-2 detection in the brain and cerebrospinal fluid of COVID-19 patients, it is still unclear whether the virus can infect the central nervous system, and which neuropathological alterations can be ascribed to viral tropism, rather than immune-mediated mechanisms. Here, we assess neuropathological alterations in 24 COVID-19 patients and 18 matched controls who died due to pneumonia/respiratory failure. Aside from a wide spectrum of neuropathological alterations, SARS-CoV-2-immunoreactive neurons were detected in the dorsal medulla and in the substantia nigra of five COVID-19 subjects. Viral RNA was also detected by real-time RT-PCR. Quantification of reactive microglia revealed an anatomically segregated pattern of inflammation within affected brainstem regions, and was higher when compared to controls. While the results of this study support the neuroinvasive potential of SARS-CoV-2 and characterize the role of brainstem inflammation in COVID-19, its potential implications for neurodegeneration, especially in Parkinson's disease, require further investigations.

Smell deficits in COVID-19 and possible links with Parkinson's disease.

Olfactory impairment is a common symptom in Coronavirus Disease 2019 (COVID-19), the disease caused by Severe Acute Respiratory Syndrome-Coronavirus 2 (SARS-CoV-2) infection. While other viruses, such as influenza viruses, may affect the ability to smell, loss of olfactory function is often smoother and associated to various degrees of nasal symptoms. In COVID-19, smell loss may appear also in absence of other symptoms, frequently with a sudden onset. However, despite great clinical interest in COVID-19 olfactory alterations, very little is known concerning the mechanisms underlying these phenomena. Moreover, olfactory dysfunction is observed in neurological conditions like Parkinson's disease (PD) and can precede motor onset by many years, suggesting that viral infections, like COVID-19, and regional inflammatory responses may trigger defective protein aggregation and subsequent neurodegeneration, potentially linking COVID-19 olfactory impairment to neurodegeneration. In the following chapter, we report the neurobiological and neuropathological underpinnings of olfactory impairments encountered in COVID-19 and discuss the implications of these findings in the context of neurodegenerative disorders, with particular regard to PD and alpha-synuclein pathology.

Case Report: The Carotid Body in COVID-19: Histopathological and Virological Analyses of an Autopsy Case Series.

Various authors have hypothesized carotid body (CB) involvement in Coronavirus Disease 2019 (COVID-19), through direct invasion or indirect effects by systemic stimuli ('cytokine storm', angiotensin-converting enzyme [ACE]1/ACE2 imbalance). However, empirical evidence is limited or partial. Here, we present an integrated histopathological and virological analysis of CBs sampled at autopsy from four subjects (2 males and 2 females; age: >70 years old) who died of COVID-19. Histopathological, immunohistochemical and molecular investigation techniques were employed to characterize Severe Acute Respiratory Syndrome - Coronavirus 2 (SARS-CoV2) viral invasion and inflammatory reaction. SARS-CoV2 RNA was detected in the CBs of three cases through Real-Time Reverse Transcription Polymerase Chain Reaction (RT-PCR). In these cases, positive immunostaining for Nucleocapsid and Spike protein were also demonstrated, mainly at the level of large roundish cells consistent with type I cells, confirming direct CB invasion. In these cases, T lymphocytes showed focal aggregations in the CBs, suggestive of local inflammatory reaction. Blood congestion and microthrombosis were also found in one of the positive cases. Intriguingly, microthrombosis, blood congestion and microhaemorrages were also bilaterally detected in the CBs of the negative case, supporting the possibility of COVID-19 effects on the CB even in the absence of its direct invasion. SARS-CoV-2 direct invasion of the CB is confirmed through both immunohistochemistry and RT-PCR, with likely involvement of different cell types. We also reported histopathological findings which could be ascribed to local and/or systemic actions of SARS-CoV-2 and which could potentially affect chemoreception.

Anatomical societies find new ways to come together in a post-Covid world.

The world has been turned upside down by a global health emergency caused by the Covid-19. Given the high contagiousness of the virus and the need to contain its spread, social distancing rules, self-isolation policies, and geographical lockdowns have been enforced globally. Over the pandemic emergency the majority of the planned in-person meetings and congresses of national and international anatomical societies have been postponed or canceled. It is unclear what the future holds, but times of crisis often present possibilities for re-thinking old ways to achieve a more critical approach. It has become increasingly clear that traditional in-person congress formats of scientific societies need to be reevaluated. Over the past year and a half, two types of congressional modalities have been trialed to address the challenge of the pandemic as far as scientific meetings are concerned: the fully virtual congress, in which case the conference program is live streamed to all of the attendees, and the hybrid congress, in which case some of the attendees physically participate at the congress's venue while others interact via a virtual platform. The current study set out to investigate the technical difficulties, social challenges, costs and sustainability, logistics and management issues linked to holding various types of congresses in the post-Covid world. Anatomical societies throughout the world are actively striving to reshape their response to the current global emergency and to uncover new types of conference modalities in the effort to keep scientific exchange alive and flourishing in the post-Covid era.

Hypopharyngeal Ulcers in COVID-19: Histopathological and Virological Analyses - A Case Report.

In coronavirus disease 2019 (COVID-19), ulcerative lesions have been episodically reported in various segments of the gastrointestinal (GI) tract, including the oral cavity, oropharynx, esophagus, stomach and bowel. In this report, we describe an autopsy case of a COVID-19 patient who showed two undiagnosed ulcers at the level of the anterior and posterior walls of the hypopharynx. Molecular testing of viruses involved in pharyngeal ulcers demonstrated the presence of severe acute respiratory syndrome - coronavirus type 2 (SARS-CoV-2) RNA, together with herpes simplex virus 1 DNA. Histopathologic analysis demonstrated full-thickness lympho-monocytic infiltration (mainly composed of CD68-positive cells), with hemorrhagic foci and necrosis of both the mucosal layer and deep skeletal muscle fibers. Fibrin and platelet microthrombi were also found. Cytological signs of HSV-1 induced damage were not found. Cells expressing SARS-CoV-2 spike subunit 1 were immunohistochemically identified in the inflammatory infiltrations. Immunohistochemistry for HSV1 showed general negativity for inflammatory infiltration, although in the presence of some positive cells. Thus, histopathological, immunohistochemical and molecular findings supported a direct role by SARS-CoV-2 in producing local ulcerative damage, although a possible contributory role by HSV-1 reactivation cannot be excluded. From a clinical perspective, this autopsy report of two undiagnosed lesions put the question if ulcers along the GI tract could be more common (but frequently neglected) in COVID-19 patients.

Sympathetic activation: a potential link between comorbidities and COVID-19.

In coronavirus disease 2019 (COVID-19), higher morbidity and mortality are associated with age, male gender, and comorbidities, such as chronic lung diseases, cardiovascular pathologies, hypertension, kidney diseases, diabetes mellitus, and obesity. All of the above conditions are characterized by increased sympathetic discharge, which may exert significant detrimental effects on COVID-19 patients, through actions on the lungs, heart, blood vessels, kidneys, metabolism, and/or immune system. Furthermore, COVID-19 may also increase sympathetic discharge, through changes in blood gases (chronic intermittent hypoxia, hyperpnea), angiotensin-converting enzyme (ACE)1/ACE2 imbalance, immune/inflammatory factors, or emotional distress. Nevertheless, the potential role of the sympathetic nervous system has not yet been considered in the pathophysiology of COVID-19. In our opinion, sympathetic overactivation could represent a so-far undervalued mechanism for a vicious circle between COVID-19 and comorbidities.

The potential role of the carotid body in COVID-19.

The carotid body (CB) plays a contributory role in the pathogenesis of various respiratory, cardiovascular, renal, and metabolic diseases through reflex changes in ventilation and sympathetic output. On the basis of available data about peripheral arterial chemoreception and severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2), a potential involvement in the coronavirus disease 2019 (COVID-19) may be hypothesized through different mechanisms. The CB could be a site of SARS-CoV-2 invasion, due to local expression of its receptor [angiotensin-converting enzyme (ACE) 2] and an alternative route of nervous system invasion, through retrograde transport along the carotid sinus nerve. The CB function could be affected by COVID-19-induced inflammatory/immune reactions and/or ACE1/ACE2 imbalance, both at local or systemic level. Increased peripheral arterial chemosensitivity and reflex sympatho-activation may contribute to the increased morbidity and mortality in COVID-19 patients with respiratory, cardiovascular, renal, or metabolic comorbidities.