{'fraction_non_alphanumeric': 0.022527472527472527, 'fraction_numerical': 0.006043956043956044, 'mean_word_length': 5.621818181818182, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 1, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Exogenous cholesterol acquisition signaling in LH-responsive MA-10 Leydig cells and in adult mice.

MA-10 cells, established four decades ago from a murine Leydig cell tumor, has served as a key model system for studying steroidogenesis. Despite a precipitous loss in their innate ability to respond to luteinizing hormone (LH), use of a cell permeable cAMP analog for induction ensured their continued use. In parallel, a paradigm that serum-free conditions are essential for trophic steroidogenic stimulation was rationalized. Through selection of LH-responsive single-cell MA-10Slip clones, we uncovered that Leydig cells remain responsive in the presence of serum in vitro, and that exogenous cholesterol delivery by lipoproteins provided a significantly elevated steroid biosynthetic response (>2-fold). In scrutinizing the underlying regulation, systems biology of the MA-10 cell proteome identified multiple Rho-GTPase signaling pathways as highly enriched. Testing Rho function in steroidogenesis revealed that its modulation can negate the specific elevation in steroid biosynthesis observed in the presence of lipoproteins/serum. This signaling modality primarily linked to regulation of endocytic traffic, is evident only in the presence of exogenous cholesterol. Inhibiting Rho function in vivo also decreased hCG-induced testosterone production in mice. Collectively, our findings dispel a long-held view that use of serum could confound or interfere with trophic stimulation, and underscore the need for exogenous lipoproteins when dissecting physiological signaling and cholesterol trafficking for steroid biosynthesis in vitro. The LH-responsive MA-10Slip clones derived in this study present a reformed platform enabling biomimicry to study the cellular and molecular basis of mammalian steroidogenesis.