Neurotrophic factor prosaposin (PS) is a precursor for saposins A, B, C, and D, which are activators for specific sphingolipid hydrolases in lysosomes. Both saposins and PS are widely contained in various tissues. The brain, skeletal muscle, and heart cells predominantly contain unprocessed PS rather than saposins. PS and PS-derived peptides stimulate neuritogenesis and increase choline acetyltransferase activity in neuroblastoma cells and prevent programmed cell death in neurons. We previously detected increases in PS immunoactivity and its mRNA in the rat facial nucleus following facial nerve transection. PS mRNA expression increased not only in facial motoneurons, but also in microglia during facial nerve regeneration. In the present study, we examined the changes in immunoreactivity of the PS receptors GPR37 and GPR37L1 in the rat facial nucleus following facial nerve transection. Following facial nerve transection, many small Iba1- and glial fibrillary acidic protein (GFAP)-positive cells with strong GPR37L1 immunoreactivity, including microglia and astrocytes, were observed predominately on the operated side. These results indicate that GPR37 mainly works in neurons, whereas GPR37L1 is predominant in microglia or astrocytes, and suggest that increased PS in damaged neurons stimulates microglia or astrocytes via PS receptor GPR37L1 to produce neurotrophic factors for neuronal recovery.

Background: Intravascular large B-cell lymphoma (IVLBCL) is a rare entity among large B-cell non-Hodgkin lymphomas and is often difficult to diagnose. We report the case of a patient with IVLBCL who presented with central nervous system (CNS) symptoms alone, in which positron emission tomography (PET) enabled a rapid and accurate diagnosis. Case Description: An 81-year-old woman was admitted to our hospital with a 3-month history of gradually progressive dementia and declining spontaneity. Magnetic resonance imaging revealed multiple hyperintense lesions bilaterally on diffusion-weighted imaging without enhancement on gadolinium-enhanced T1-weighted imaging. Laboratory findings showed elevated serum lactate dehydrogenase (626 U/L) and soluble interleukin-2 receptor (sIL-2R) (4692 U/mL). Cerebrospinal fluid (CSF) analysis showed slightly elevated levels of protein (166 mg/dL) and lymphocytic cells (29/μL), and β2-microglobulin (β2-MG) (4.6 mg/L) was highly elevated. Whole-body computed tomography revealed faint ground-glass opacities in the upper and middle lung fields and diffuse enlargement of both kidneys without lymph node swelling. 18F-fluorodeoxyglucose (FDG)-PET showed diffuse and remarkably high FDG uptake in both upper lungs and kidneys without uptake by lymph nodes, suggesting a malignant hematological disease. IVLBCL was confirmed histologically by incisional random skin biopsy from the abdomen. Chemotherapy using R-CHOP regimen in combination with intrathecal methotrexate injection was started on day 5 after admission and follow-up neuroimaging showed no signs of recurrence. Conclusion: IVLBCL presenting with CNS symptoms alone is rare and often has a poor prognosis associated with delayed diagnosis, and various evaluations (including systemic analysis) are therefore necessary for early diagnosis. FDG-PET, in addition to identification of clinical symptoms and evaluation of serum sIL-2R and CSF β2-MG, enables rapid therapeutic intervention in IVLBCL presenting with CNS symptoms.

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