Pandey, S. N. | Search bioRxiv

bioRxiv2025

Structural Validation of the Intermediate Leptomeningeal Layer in the Human Central Nervous System

Traditionally, the human central nervous system (CNS) is described as having three meningeal layers, from outer to inner: dura mater, arachnoid mater, and pia mater. The arachnoid and pia mater are called the leptomeninges, and the space between them is filled with cerebrospinal fluid (CSF). Using gross dissection, light microscopy, and ultrastructural analysis of fresh postmortem and cadaveric CNS specimens spanning fetal to adult ages (N=61), we demonstrate a fibrocellular intermediate leptomeningeal layer (ILL) from the cortex to the caudal end of the spinal cord. The ILL divides the subarachnoid space (SAS) into two distinct structural compartments, through which vessels and nerves pass. The ILL shows unique structural features, such as dips into the brains sulci and fissures, as a double-fold membrane that bears intra-layer trabeculae, carries vessels, and forms the perivascular sheath. Moreover, throughout the CNS, it appears to be a non-sieved barrier, characterized by the presence of tight and adherens junctions. ILL, predominantly in the spinal cord, contains macrophage-like cells, indicating its layer-specific immune properties. The ILL warrants recognition as a distinct human meningeal layer with potential barrier and immune functions. SignificanceO_ST_ABSAn Intermediate Leptomeningeal Layer encloses the Central Nervous System in HumansC_ST_ABSThe integrated analysis of our macroscopic, microscopic, and ultrastructural study provides robust support for an intermediate leptomeningeal layer (ILL) in the subarachnoid space (SAS) of the human central nervous system (CNS) along the entire neural axis. The ILL is a fibrocellular macroscopic structure, with restricted permeability, that divides the cerebrospinal fluid (CSF)-filled SAS into two distinct structural compartments. Uniquely, ILL revealed the presence of cells with macrophage-like properties, suggesting a possible role in immune surveillance. The ILL may redefine the established concept of protective coverings of CNS, CSF circulation dynamics, and the role of leptomeninges in health and disease, including drug delivery.

neuroscience↗

bioRxiv2020

Relevance of enriched expression of SARS-CoV-2 binding receptor ACE2 in gastrointestinal tissue with pathogenesis of digestive symptoms, diabetes-associated mortality, and disease recurrence in COVID-19 patients

IntroductionCOVID-19 is caused by a new strain of coronavirus called SARS-coronavirus-2 (SARS-CoV-2), which is a positive sense single strand RNA virus. In humans, it binds to angiotensin converting enzyme 2 (ACE2) with the help a structural protein on its surface called the S-spike. Further, cleavage of the viral spike protein (S) by the proteases like transmembrane serine protease 2 (TMPRSS2) or Cathepsin L (CTSL) is essential to effectuate host cell membrane fusion and virus infectivity. COVID-19 poses intriguing issues with imperative relevance to clinicians. The pathogenesis of GI symptoms, diabetes-associated mortality, and disease recurrence in COVID-19 are of particular relevance because they cannot be sufficiently explained from the existing knowledge of the viral diseases. Tissue specific variations of SARS-CoV-2 cell entry related receptors expression in healthy individuals can help in understanding the pathophysiological basis the aforementioned collection of symptoms. Materials and MethodsThe data were downloaded from the Human Protein Atlas available at (https://www.proteinatlas.org/humanproteome/sars-cov-2) and the tissue specific expressions (both mRNA and protein) of ACE2 and TMPRSS2 as yielded from the studies with RNA sequencing and immunohistochemistry (IHC) were analyzed as a function of the various components of the digestive tract. A digestive system specific functional enrichment map of ACE2 gene was created using g:profiler (https://biit.cs.ut.ee/gprofiler/gost) utility and the data were visualized using Cytoscape software, version 3.7.2 (https://cytoscape.org/). ResultsThe correlated expression (transcriptomic and proteomic) of ACE2 (to which SARS-CoV-2 binds through the S-spike) was found to be enriched in the lower gastrointestinal tract (GIT) (highest in small intestine, followed by colon and rectum), and was undetectable in the upper GIT components: mouth cavity (tongue, oral mucosa, and salivary glands), esophagus, and stomach. High expression of ACE2 was noted in the glandular cells as well as in the enterocytes in the lining epithelium (including brush border epithelium). Among other digestive system organs, Gall bladder (GB) showed high expression of ACE2 in glandular cells, while any protein expression was undetectable in liver and pancreas. TMPRSS2 was found enhanced in GIT and exocrine glands of pancreas, and co-localized with ACE2 in enterocytes. ConclusionsBased on the findings of this study and supportive evidence from the literature we propose that a SARS-CoV-2 binding with ACE2 mediates dysregulation of the sodium dependent nutrient transporters and hence may be a plausible basis for the digestive symptoms in COVID-19 patients. ACE2 mediated dysregulation of sodium dependent glucose transporter (SGLT1 or SLC5A1) in the intestinal epithelium also links it to the pathogenesis of diabetes mellitus which can be a possible reason for the associated mortality in COVID-19 patients with diabetes. High expression of ACE2 in mucosal cells of the intestine and GB make these organs potential sites for the virus entry and replication. Continued replication of the virus at these ACE2 enriched sites may be a basis for the disease recurrence reported in some, thought to be cured, patients. Graphical Abstract O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

pathology↗